Until the moment Sputnik launched in 1957, the night sky remained a wilderness untouched by the hand of Man. People who looked up, and who did so far enough away from the glare of city lights, could see pretty much the same sky as every other human had since the dawn of consciousness.

Since that day, however, things have changed. Sputnik itself was not that bright, but its rocket booster was, and for a few days it shone as bright as a first magnitude star. Today there are tens of thousands of artificial objects orbiting our world, and on any clear night the impact of our work can clearly be seen.

Some hail the progress this has brought. The majority of active satellites now in orbit belong to the Starlink constellation, a massive piece of infrastructure that provides Internet connections across the world, as well as aiding the espionage and military capabilities of the United States. But it has come at a price.

The night sky is no longer a pristine wilderness. Astronomers have suffered, as satellites leave bright trails across their images. Debris, in the form of abandoned satellites and rockets, is gradually building up in orbit. The risks of a collision, or of parts of a falling satellite hitting and killing someone, are rising.

This loss looks certain to continue in the coming years. More Starlink satellites will be launched, especially if SpaceX masters their Starship rocket. Musk has said he wants to launch a million data centres into orbit to power AI. Amazon has started building a huge constellation of their own. China is doing the same, and many others have announced plans.

One of the brightest objects in the sky is now not a planet or a star, but BlueWalker 3, a satellite aiming to provide cellular phone service from space. Reflect Orbital, an American startup, hopes to soon deploy gigantic mirrors in orbit. If they succeed in this rather nonsensical idea, they will create objects that shine as bright as the full Moon.

All this, the European Southern Observatory recently warned, will mean the end of the night sky. Instead of a heavens full of stars and wonder, we will see only a sky shaped by our own hands. In the place of planets, we will see satellites beaming data and turning night into day.

For astronomers, the prospect is frightening. Major astronomical projects, including the Vera Rubin’s ten-year survey and the European Extremely Large Telescope, may be for naught. If the sky holds more than about one hundred thousand satellites, ESO calculates, then astronomy as we know it will become impossible.

It is troubling that much of this change is coming about without proper discussion. The American government has recently approved the launch of Reflect Orbital’s bright satellites – a decision that will be felt by people across the planet, not just in America. They did not consider the impact such giant mirrors will have on the world, nor accept responsibility for the consequences of their actions on the night sky.

The Oldest Impact Crater On Earth

Some of the oldest rocks on Earth lie in the Pilbara region of Western Australia. It is here that we have found the earliest signs of life on our planet, in the form of mineral deposits and other structures probably created by organisms living more than three billion years ago.

The extreme age of this region makes it a good place to look for evidence about the early Earth. One debate surrounds the origin of the continents: many geologists think they were created by immense plumes of molten rock and heat welling up from the interior of the planet. But a team led by Tim Johnson at Curtin University thinks the energy to form them instead came from massive asteroid strikes.

To find evidence to support this idea, they headed to Pilbara in search of ancient impact craters. They found one in May 2021, in a region called North Pole Dome. There is no actual crater there, at least not any more, but they did find signs that the local rocks had experienced an impact shock. In part, this evidence came in the form of geological structures called shatter cones.

They concluded the impact had happened in the distant past, probably more than three billion years ago. But an alternative study, led by a group from Harvard, later reached a different conclusion. They agreed there had been an impact, but thought it had happened much more recently. The asteroid responsible, they found, could have struck the Earth ‘just’ four hundred million years ago.

Now, the Australian team has hit back. They carried out a more detailed analysis of the rocks at the site of the crater, and examined the crystals within them. Some showed an age of 3.4 billion years, and were probably formed along with the rocks. But others showed signs of having experienced a sudden shock, like an impact, and these were dated to about three billion years of age.

Alongside this, they found another mineral, apatite, that forms when heat drives water through fractured rock. As with the shocked crystals, this was dated to an age of about three billion years. Together, the two pieces of evidence suggest we really are looking at the oldest known impact crater on Earth.

Euclid’s Ancient Quasars

The European Space Agency announced the discovery of the earliest known quasars in the universe. They were found by the Euclid Space Telescope, an observatory dedicated to the study of distant galaxies and to the hunt for dark matter and dark energy.

Quasars are, in essence, extremely active galaxies. Their inner black holes are consuming vast amounts of gas and dust and other material, and this creates a furious disc of material swirling around their centres. The result is a hot and bright galactic core, one visible across extraordinary distances.

Indeed, many quasars are far away and are visible as they were billions of years ago. But spotting the oldest quasars has so far been challenging. They are distant, which makes them appear faint, and they can look more like stars than galaxies.

The Euclid Space Telescope, however, spotted thirty-one of the oldest quasars known. Some were formed in the first billion years after the Big Bang. They seem to be dusty objects, filled with stars forming at a rapid pace.

It is possible the James Webb Space Telescope has seen even earlier quasars, or perhaps objects that eventually evolve into quasars. Since it launched, Webb has spotted dozens of ‘little red dots’ in the early universe. Astronomers are still divided about what they are, but one theory holds that these are primitive galaxies with active central black holes.

If so, the work of the two telescopes may be helping to close a gap in our understanding of how quasars came to be. Many questions, of course, still remain. Astronomers have plenty to learn from these new observations of the early years of the cosmos.

The Greatest Survey Begins

The Vera Rubin Observatory began an ambitious ten-year project to survey the night sky. The Legacy Survey of Space and Time, or LSST, aims to create a time-lapse of the heavens, showing how celestial objects change over both long and short time periods.

Vera Rubin is equipped with the world’s largest camera. It weighs three metric tons and can capture 3200 megapixels. All that power will be dedicated to the survey, and it should help the observatory spot countless objects that have so far been missed. The observatory, astronomers hope, will discover millions of asteroids and comets, search for a possible ninth planet, and hunt for traces of dark matter and dark energy.

Construction work on Rubin, built on top of a mountain in central Chile, came to an end in November last year. Since then, operators have been conducting engineering tests and optimising the quality and performance of the telescope and its instruments. They have now decided that both are good enough to start the real scientific work.

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Deep under the waves of the Pacific Ocean lie the ashes of a supernova. They exist in the form of rare isotopes of iron and plutonium, each preserved in layers of sediment laid down over long millennia. Such isotopes are not made on Earth. Instead, they can only have been forged by a giant star, and cast into space by the terrible force of its demise.

No one knows the precise shape of events. One theory holds that a massive star exploded nearby, and sent debris raining down upon our planet in a spectacular aftermath. Another argues that the dying star was more distant, the ash collected first into clouds, and only fell upon us as the Earth happened to later pass through.

However it arrived, the ash seems to be everywhere. Similar samples have been found clinging to rocks on the Moon, frozen in layers of ice laid down at the poles, and buried in sediments at the bottom of every ocean we’ve examined. All this material is indisputably of cosmic origin, and could only have been scattered by some catastrophic event.

The obvious cause would be a nearby supernova. Since the ashes seem to have arrived in two clear waves – one two million years ago, the other seven million – some think they hint at the explosions of two giant stars close to our planet. Adding support to this idea is the presence of a vast bubble stretching all around us in space, a region recently swept clear by a powerful shock wave.

At first, the blame for all this fell on Geminga, an energetic and fast-moving neutron star about eight hundred light-years away. It is, quite clearly, the remnant of a big star that exploded. But the timings don’t quite add up: its supernova probably took place about three hundred thousand years ago. It could not have made the ash we found, nor could it have been powerful enough to blow a bubble as big as the one we now see.

Instead, today’s astronomers think about a dozen giant stars have exploded around us in the past fifteen million years. Each helped sculpt the bubble, and each has scattered debris into the space it occupies. Some of these stars might have exploded close to Earth: if they did, they may well have strewn their dust across our world and its moon.

Yet questions remain. It is far from certain how this ash made its way to our planet, or how close these giant stars were to us when they died. A supernova within one or two hundred light years of Earth would have been an extraordinary event. Could one really have blazed in the sky two million years ago, showering us with its debris just as our distant ancestors were beginning to shape stones into tools?

The Slow Rain of Ash

About four hundred light-years from us lies a group of bright blue stars known as the Scorpius-Centaurus Association. These are young stars, each born in the last fifteen million years. Many of those we can see are massive stars that burn bright and die young. When we search for blame for the recent violence, Scorpius-Centaurus seems an obvious place to start.

Studies have indeed found signs of recent supernovae there. One possibly erupted two million years ago, an event that created a fast-spinning pulsar and sent the star Zeta Ophiuchi careening off into space. It might have been close enough to shower us with ash, although we are uncertain precisely where this giant star lay relative to us at the time.

This and another so far untraced event could have been responsible for the two waves of debris we see in the sediment record. But not everyone is so sure. A supernova should create a relatively short pulse of ash, and would need to be extremely close by to produce the amount seen. Yet the sediments show a longer wave than this. Neither does the timing seem to match any known mass extinction of life that would accompany such a nearby and violent event.

Instead, as a paper by Merav Opher, Avi Loeb, and J.E.G. Peek pointed out in 2024, a series of past supernovae would have scattered debris across our region of space. Over time, all this ash and dust would have settled into clouds, and these would have remained spread across the bubble otherwise swept clear by the supernova shock waves.

Every now and then, they say, the solar system passes through one of these clouds. Roughly two million years ago, we could have encountered a particularly dense ribbon of dust. If so, this would have pushed the Sun’s magnetic shield inwards, and allowed a heavy rain of ash and dust to fall upon our world for tens of thousands of years.

In this case, the supernova would not have been especially close to us. Indeed, the star could have exploded at a distance of a few hundred light-years – which is still close, but hardly dangerously so. As long as we encountered the debris cloud it left behind within a few million years, that long-ago event could still have left an imprint on our world.

Pieces of the Sky

In his book Wind, Sand, and Stars, Antoine de Saint-Exupéry remarks on the sight of black meteorites scattered across the sands of the Sahara. There is, he notes, a long, slow rain of these rocks upon the Earth. They remind us that our planet is not alone, not adrift in an empty universe. From time to time, pieces of the heavens fall upon us.

Many of these pieces are subtler and harder to spot than meteorites. The behaviour of the Sun influences the atmosphere: when a strong solar flare hits, it creates isotopes that are picked up and stored by trees. Millennia later, we can find the evidence of these ancient flares marked in their tree rings.

Cosmic dust is another of these quiet hints of a wider universe. It falls slowly on our world. Even today, supernova ash is still coming, but it is doing so at the imperceptible rate of less than a gram a year across the entire globe. To find its signature, scientists must look for the ash atom by atom, teasing it out from records laid down over extraordinary lengths of time.

Recent examinations of polar ice have spotted a subtle shift in this slow fall of dust. The rain is quietly getting heavier. This increase, they say, could mark a change in our interstellar environment; a transition from a void to a cloud, or from one cloud to another. Today we appear to be well inside one such cloud – indeed, we seem to be getting closer to its edge than to its centre.

Researchers have not yet dated precisely when we entered this cloud. Based on what we know, it was probably between ten and forty thousand years ago. All of human history, in other words, from the dawn of agriculture to the awakening of artificial minds, has taken place inside this single, small cloud. Sometime in the next few thousand years, if we last that long, we will move beyond it.

The Sun’s journey through space has been far greater than that. To our short lives, our short civilisation, the stars are almost static. Yet they are not. The ashes at the bottom of the Pacific Ocean tell us something about where we have been. But they are also a reminder that things operate on scales far beyond our own; that if you stretch a sheet under the stars, you will slowly gather their dust.

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Hello!

Thanks for reading The Quantum Cat, a newsletter covering space, physics, and the exploration of both. If you have been enjoying the newsletter, I wanted to share what paid subscribers have been reading and what comes next.

Until now, paid content has consisted of additional in-depth articles every month. Over the past year, these have focused on two broad areas. One, Visions of the Cosmos, looks at the art and photography behind astronomy. The other, Physics of the Ancient World, explores how people from Ancient Greece to Babylonia understood the world around them.

Over the next few months, I plan to continue looking into these areas. Upcoming paid articles will discuss the work of Euclid, of Archimedes, and how other ancient people in India, the Americas, and Australia developed their own ideas about physics and astronomy. I will also be covering the drawings of Galileo, the astrology of Kepler, and the canals of Mars. Before all that, however, the next paid article will look at the extreme engineering necessary to send a probe closer to the Sun than ever before.

You can find the paid archives on my Substack page (view them here). If you are already a paid subscriber, or if you decide to become one, you will have immediate access to the full archives as well as to all upcoming articles.

As always, please only subscribe if you want to. But if you do decide to take a paid subscription - thank you. It is through your support that I can continue researching and writing these newsletters. It genuinely means a lot to me that readers are willing to fund this effort.

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What’s New in the Paid Archives

Far out in space, far beyond the orbits of Neptune and Pluto, beyond even that of Sedna, lies a vast cloud of ice and dust.

This cloud extends far around our Solar System. It is called the Oort Cloud, and although we have never directly seen it, bits of it occasionally fall into the inner Solar System. When they do, they appear as comets, tracing long orbits from the outer ice to the inner warmth. Some of them, the longest of the long-period comets, can spend a million years or more falling inwards from the Oort Cloud until the moment they appear in our skies.

Because the Oort Cloud is so big – stretching outwards for at least a light year – astronomers have long thought it should occasionally be disturbed by passing stars. At times these stars can come surprisingly close to our Sun, and when they do, their influence should upset the orbits of objects in the Oort Cloud.

Some objects will be thrown outwards. Indeed, the handful of interstellar comets we have seen may be the result of something similar happening around other stars. But some will be knocked inwards. And this should create something like a shower of comets falling towards the inner Solar System; a visible marker of passing stars that appears a few hundred thousand years after they arrive.

Data from the Gaia telescope tells us that one such star should have approached about two and a half million years ago. That star – HD 7977 – currently lies two hundred and fifty light years from Earth. But its trajectory shows that it must have passed close to us. Exactly how close is uncertain, but it may have come within a fifth of a light-year of the Sun.

That would put it well within the Oort Cloud. In a recent pre-print paper, two researchers – Nathan Kaib and Sean Raymond – modelled the effect this close passage would have had on the Solar System. Like previous studies, they found that HD 7977 would have sent a wave of comets raining down on the inner planets.

In an effort to work out how close HD 7977 came, however, they modelled different possible close approaches. They then compared the results of these models with the orbits of real observed comets. These, they found, show a pattern that can be explained if HD 7977 had passed within a tenth of a light-year of our Sun.

That is remarkably close, perhaps closer than any other star has come in the past few hundred million years. If the conclusions are accurate, then this approach could even have altered the orbit of our planet, changed the climate, and so affected the course of evolution at a critical moment for the origins of our species.

More data from Gaia will be released in the next few years. When it is, astronomers hope to better pin down the trajectory of HD 7977, and thus work out with more accuracy how close it came to the Sun. If we can do that, we can more precisely model the impact it must have had on the Solar System and on us.

If Kaib and Raymond are right, though, we are still living through the aftermath of this close approach. Though HD 7977 is now two hundred and fifty light years away, the comets we see in the sky today may still be part of a long shower triggered by its ancient passage.

Time for an Upgrade at the Large Hadron Collider

The Large Hadron Collider is a marvel of modern engineering. It is the world’s largest and highest-energy particle collider, a machine that has the power consumption of a small city, and that collides sub-atomic particles with a ferocity seen nowhere else on Earth.

This all means it can probe the laws of physics at a deeper and more fundamental level than any other scientific experiment in the world. Yet, last week, on June 29, the instruments of the Large Hadron Collider ceased work. The particle beams were shut down, the collisions put on hold, and the experiments suspended.

For the next two years, its engineers and scientists will conduct a campaign to maintain, repair, and upgrade the collider. This effort, named the Long Shutdown 3, should result in an enhanced machine. By the end, it will be capable of more particle collisions than ever achieved in the past.

Yet the amount of work that must be done to meet this goal is considerable and highly challenging. Over the next few months, operators will need to warm up the collider’s superconducting magnets. These are normally kept at a temperature just two degrees above absolute zero. Warming them to a temperature where they can be accessed and repaired takes several months alone.

After that, engineers will reconfigure many of the instruments and experiments deployed at the collider. One key target is to increase the luminosity of the collider – a measure, essentially, of how many collisions take place when its beams cross. The higher its luminosity, the more data the collider can gather.

This work, CERN says, will have two key benefits. First, there is the engineering knowledge gained. The LHC operates at the frontiers of our abilities, and upgrading it forces innovation in fields from superconductivity to industrial engineering. But second, of course, is the opportunity for new science.

The upgraded LHC will produce much more data on particle collisions, and offer a more stringent test of how the fundamental laws of nature operate. There is nowhere else on Earth capable of matching this ability. If we want to make discoveries about the subatomic world, this upgrade may be our best hope yet.

Euclid Paves the Way for Roman

At the end of June, the European Space Agency released the largest and most detailed image of the centre of our galaxy yet captured. It shows more than sixty million stars, almost all of them crowded into the central bulge of the Milky Way, and was captured by the Euclid Space Telescope.

In some ways, this image was an exception for Euclid. Most of its time is spent surveying distant galaxies, an effort that should help astronomers map the distribution of dark matter throughout the cosmos. Images of our own galaxy, no matter how beautiful they are, don’t do a lot to help with this goal.

But they will help support the efforts of an upcoming telescope. In August, NASA hopes to launch the Nancy Grace Roman Space Telescope. Although its domain of work will be wide, this new observatory will dedicate some of its time to monitoring the heart of our galaxy. Astronomers expect this study will help spot tens of thousands of new stars, planets, and other things like black holes.

Euclid’s operators thus accepted a special request to get an early start on this survey. Over a period of about twenty-six hours, they paused the observatory’s main work and redirected it towards the heart of the galaxy. The resulting image – both beautiful and unprecedented – offers a preview of what the Roman telescope will do, and gives astronomers an early start on their ambitious effort to monitor the centre of the Milky Way.

A Trace of Life on Mars?

Over the past two years, scientists have been investigating possible traces of ancient life on Mars. These are not fossils, or even anything close, but rather chemical and mineral signatures that may have been deposited by simple life forms living in the rivers that once flowed over the Martian landscape.

This evidence, they concluded last year, is a potential sign of life but not a certain one. The minerals, which were uncovered by the Perseverance rover, could have been created by biology. But they could also have been created by a chemical or geological process, and so far we cannot rule out that possibility.

Now, new evidence has emerged from Perseverance’s instruments. One of these, a device called SHERLOC, spotted signs of large carbon-containing molecules. These were found both near the intriguing minerals and on another rock lying about a hundred metres from it.

On Earth, such molecules are often made by living organisms. Yet they can also be made by other processes – perhaps by chemical reactions, or by the fall of a meteorite. As before, these represent a potential sign of ancient life. But the evidence is still not conclusive.

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The first principles of the universe are atoms and empty space; everything else is merely thought to exist.
- Diogenes Laertius on Democritus

Ours is not an empty world.

Artists sometimes speak of horror vacui, the idea that nature abhors a vacuum. Humans certainly do. Emptiness – the blank canvas, the empty page, the silent room – is somehow disturbing, unsettling, something we seek to fill with colour, with words, with sound. The empty moment is filled with idle activity; the blank sheet is covered in scribbles and doodles.

For Aristotle, this basic instinct reflected a deeper truth of reality. Nature abhors a vacuum. Create a void, he said, and the fullness of the world immediately rushes in. Emptiness cannot last; it cannot even really exist, he wrote, and the very concept of it was almost absurd. The so-called vacuum, he once joked, was itself a vacuous idea.

And yet it somehow wasn’t. Aristotle’s writings on the void have long rung hollow. Something seems off in his dismissal, in his reluctance to consider the possibility of nothingness. The root of this aversion has always been mysterious: some think it was religious in nature, or based on a conviction about natural perfection, or even just down to a dislike, common to us all, of the idea of pure emptiness.

In the centuries before Aristotle, a lively debate had raged over the nature of nothingness. Some had found it a hard thing, almost an impossible thing, to talk about: Parmenides, writing about two hundred years earlier, had argued that since nothingness was by definition nothing, there was nothing at all you could say about it.

But there was, Leucippus and Democritus argued, a sense in which ‘nothing’ must exist. It was only through empty space, through the void, that things could move. Deny the possibility of emptiness, they said, and you deny the reality of motion and change – an idea that Zeno explored with great effect in his series of famous paradoxes.

The world they described was one filled with atomos, the unchanging and indivisible components of matter. It was these atoms that moved through the void, and that by rearranging themselves, allowed for change to occur. The necessity of the void was simple: for an atom to move, it had to both leave an empty space behind it and find an empty space to move into.

Far from finding the void abhorrent, their description made it essential. With no voids, change would become impossible. Without the atomos, the world would effectively be a blank sheet. Together, the void and the atom were thus responsible for all the fullness of existence: all the colours, all the smells, all the sounds, all the messy detail that makes up reality.

Nature, a fragment of Democritus tells us, was “by convention sweet, by convention bitter, by convention hot, by convention cold, by convention colour: but in reality atoms and the void.”

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For a few hours, it seemed close to the nightmare scenario.

On June 5, mission control in Houston directed the astronauts on board the International Space Station to take emergency shelter. In a moment of high drama, five of them entered a docked Dragon capsule and began preparing for a fast and unexpected return to Earth. At fault was an air leak. The station was losing air through an ageing module, and the risks were deemed so serious that NASA ordered immediate action.

The module at fault is known as PrK. It is a small tunnel that connects the key Russian Zvezda module with a docking port. Typically, this port is used to dock the Russian Progress capsule, and the tunnel is used to transfer cargo in and out of the docked spacecraft.

But for several years, the tunnel has been causing problems. Leaks were first found in September 2019, at which time they seemed to be small and manageable. But over time they have worsened. Cosmonauts have repeatedly patched cracks with sealant, but this has not solved the problem.

To reduce the impact, the tunnel is usually closed and left unpressurised. But when cosmonauts need to access the Progress capsule, they must repressurise it. When they do, other precautions are taken – including closing other interior hatches in the station to reduce the risks of air loss.

As cosmonauts worked in the tunnel in early June, however, they noticed an increase in the rate at which air was escaping the module. In the past, such leaks have been fixed by using a sealant. This time, however, they apparently elected to make a more radical fix. Details are sparse, but it seems two cosmonauts were planning to cut into the structure of the module to better access the leak.

As they prepared for this, the other five astronauts on board – three Americans, one French, and one Russian - took shelter inside Dragon. Controllers apparently feared a catastrophic outcome: one in which the leaks rapidly spread, the tunnel split open, and air rushed out of the station. If that had happened, Dragon would have departed. The other two cosmonauts would have escaped on a Soyuz capsule, and for the first time in two decades the station would have been abandoned.

Fortunately, however, the situation lasted only two hours. Roscosmos later said the structural repair work had been paused and the situation would be evaluated. According to more recent reports, Roscosmos has now decided to permanently close the tunnel instead of attempting the potentially dangerous repair.

Still, the event is a warning sign. The station is ageing. NASA has hinted at wanting to continue operations on the station into the 2030s, at least until the point at which a smaller replacement is available. An early abandonment of the station would sharply cut the spaceflight programs of both America and Russia. Indeed, the only remaining station would be Chinese, and that would add to the sense that America is ceding influence in space to its geopolitical rival.

For now, operators and astronauts must deal with issues as they arise. Alongside the air leaks, controllers are now dealing with problems in the station’s robotic arm. The Canadarm, they say, will need a spacewalk to get it functioning properly again.

The First of the Nuclear Clocks

The best clocks on Earth are so accurate they would not have erred by a single second in all the years since the Big Bang.

We can do better. All clocks need some kind of reference frequency to count out the passing of time. In the past this took the form of the Earth’s rotation, the swing of a pendulum, or the resonant vibrations of a crystal of quartz. Today, we use more sophisticated means.

In modern atomic clocks, the frequency is determined by electrons inside an atom. The laws of quantum physics tell us these electrons can only occupy a set of fixed energy levels. To jump from one level to another, an electron needs to receive a precise amount of energy, and this can be given by incoming radiation of a precise frequency. From this, we can obtain a natural frequency that can be used to count the seconds.

In theory this approach can track time almost perfectly. In practice, however, the world is messy and disturbances are unavoidable. This places a limit on the accuracy that can be obtained, and means that although an atomic clock could have almost perfectly counted the seconds since the Big Bang, it cannot do so forever.

Yet clocks that rely not on electrons, but on the protons and neutrons of the atomic nucleus, might do better. Like electrons, these can jump between energy levels. But they are more sheltered, which means they are less affected by external disturbances. A nuclear clock, one based on the atomic nucleus, could be more accurate than one based on electrons.

Of course, things are harder in practice. Only atoms of thorium-229, a rare isotope of a radioactive element, have proven suitable for clocks of this kind. They can be made to jump by use of a laser, though one of a difficult kind to build and control.

Recently, two teams – one in China, one in Europe – announced they had built the first nuclear clocks based on thorium-229. Although each team took a slightly different approach, they each produced clocks of similar quality. Together, they are the first to demonstrate the idea, and so prove that nuclear clocks are indeed possible.

They are not yet more accurate than the best atomic clocks. But these are early days. Future improvements should build on these initial advances, and eventually allow for even more precise counting of time than is possible today. That, researchers say, will allow us to probe reality even more closely, and perhaps to cast light on some of the deepest mysteries of time and space.

Black Hole Winds

At the heart of the Milky Way lies a supermassive black hole known as Sagittarius A*.

Like most such beasts, this black hole is surrounded by a cloud of gas, dust, and stars. Much of this is trapped in orbit around the black hole, spiralling slowly towards the point at which it will be consumed. Yet as matter falls it heats up, and this heat drives winds blowing away from the black hole.

These winds are an inevitable side-effect of how black holes feed. They cannot cease, but they can vary in power. When black holes go on a feeding frenzy, their winds strengthen into powerful jets, as seen in galaxies like Centaurus A. In galaxies like our own, where the black hole is consuming matter at a sedate pace, the winds should be gentler.

Until now, however, the winds of Sagittarius A* were missing. This is partly because the dust and gas around the black hole obscure our view of the surrounding region. Over the past five years, however, Mark Gorski and Lena Murchikova of Northwestern University have made careful observations of the gas in the centre of the galaxy.

With these measurements they were able to map out the region around the black hole. That revealed a gap, a cone-shaped region which seems to have been swept clear of gas. The reason, they say, must be the winds coming from Sagittarius A*.

If so, this is the first clear evidence of our black hole’s winds. More observations should tell us how fast the wind is blowing, and perhaps how it has changed over time. That should give insight into how much matter the black hole is consuming, and whether it has gone through periods of activity in the recent past.

The Silent Interstellar Comet

As far as we know, the comet 3I/Atlas is an extraordinarily old lump of dust and ice. It is remarkable for its origin: the comet was born around a distant star, and has since spent much of its life traversing the vast gulfs of interstellar space.

This alone is astonishing. Yet some imagine the comet to be something more: in particular, the astronomer Avi Loeb has spent a considerable amount of time wondering if 3I/Atlas is in fact a relic of alien technology. There is little evidence for this. 3I/Atlas looks like a comet, acts like a comet, and moves like a comet.

It also shows no signs of trying to communicate with us or anyone else. After the comet was first discovered, the SETI institute began monitoring it for signs of radio signals. Yet, as they reported earlier this month, they detected nothing. Whatever else 3I/Atlas might be doing, it is not sending messages via radio.

Of course, aliens may have access to technologies far beyond our knowledge. Yet in the absence of any compelling evidence at all, we should conclude that 3I/Atlas is what it appears to be: a remarkable but completely natural comet.

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“The next time the world tunes in to watch astronauts fly around the Moon”, NASA boss Jared Isaacman said on May 19, “they will be taikonauts”.

China has not yet announced any such mission, which would likely replicate either Artemis II or Apollo 8. But it is not really in doubt that such a mission is coming, and that it may happen soon. Over the past few months, China has conducted tests of both its crew capsule, Mengzhou, and of its Long March 10A booster, the rocket that will propel astronauts towards the Moon.

For American politicians, the possibility that China might beat America back to the lunar surface is of deep concern. Isaacman has responded to these worries by pushing NASA to move faster and to start building out a base on the surface. America, he has said, “will never again give up the Moon”.

Artemis IV, the mission which might see Americans leave footprints on the Moon for the first time since 1972, is now scheduled to take place in 2028. If it launches on time, or at least before 2030, America has a good chance of beating China to the lunar surface.

Unfortunately, the past month saw two big setbacks in America’s efforts to do this. First was the twelfth launch of SpaceX’s Starship rocket. NASA plans to use this as a landing craft, the vessel that will take astronauts on the final leg of the trip to the surface and back. SpaceX, however, has struggled to get Starship ready in time.

May’s flight was supposed to change things. Over the past few months, SpaceX’s engineers have built an improved version of Starship, one they call V3. It is supposed to fix many of the issues that bedevilled the previous version, and so clear the way towards attempting a Moon landing.

Yet the test flight showed only mixed results: during ascent the rocket suffered from failed engines, and SpaceX was unable to steer the booster back to its target splashdown point. As the upper stage, ‘the ship’, flew on, it too suffered from engine problems. SpaceX abandoned some of their planned tests, though they did manage to demonstrate the ability to deploy dummy satellites. The ship at least made it back through the atmosphere in one piece, and came to a partially controlled ‘landing’ before it toppled into the ocean.

The next test flight may do better. But it is inescapable that things are not going as well as hoped. After twelve flights, SpaceX appears stuck, doomed to endlessly repeat the same suborbital trajectory with mixed results. To get to the Moon they need to break out of this loop. If it wants to get there before China, Starship almost certainly need to reach a proper orbit sometime this year.

In recent months, NASA seemed to be building a backup plan. This would have used a lander built by Blue Origin, a company owned by Amazon founder Jeff Bezos. But last week Blue suffered a major setback of its own. While their New Glenn rocket was undergoing tests in Florida, it suddenly and dramatically exploded in an enormous fireball.

The surrounding launch facilities have been badly damaged. How much this will set things back remains unclear – but it is clearly a serious blow. It would be a surprise if Blue Origin is able to launch again this year. As a result, it may not just be the next voices from the Moon that are Chinese. The next footprints may be too.

The Snowball Earth

Our world has not always been blue and green. For a while it was purple: the earliest photosynthetic life might have used retinal instead of chlorophyll, and this would have given the planet a purplish tinge. Later – during a long stagnant period geologists have nicknamed the Boring Billion – other creatures may have turned the oceans a milky black.

Around six hundred million years ago, some scientists think the Earth became a snowball. Ice sheets would have crept outwards from the poles, and eventually covered almost the entire planet. The equator would have been as cold as Antarctica is today, and even if it wasn’t frozen, the tropics would at least have been covered in an icy slush.

In theory, this kind of frozen world is perfectly stable. Ice reflects sunlight and heat, and this forms a feedback loop that keeps the planet cold. Global ice sheets may have emerged on multiple occasions, stuck around for millions of years, and only receded as something – volcanoes or meteor impacts perhaps – created enough warming to knock the world into a different stable climate.

Since then, however, the ice sheets have either vanished completely – as they did in the Jurassic period – or stuck around the poles, where they are found today. For some reason, Snowball Earths don’t seem to happen any more.

There are two possible explanations as to why not. One theory suggests that something has changed, and thus made global glaciation impossible. But others argue that supporters of the Snowball Earth are simply wrong, and that our planet has never frozen over entirely.

In a recent study, Erica Bisesi of the Astronomical Observatory of Trieste tested the first idea by modelling the conditions that may have prevailed on the Earth during such a snowball scenario. The last time it happened, she points out, the landmasses were fused into a single supercontinent named Rodinia that straddled the equator. Plants and trees had not yet emerged, so this continent was bare and rocky.

That would have made the Earth more reflective. The Sun was also cooler in the past, and half a billion years ago our planet would have received about five percent less heat than it does today. Together, these two factors would have made the world colder, Bisesi says, and more susceptible to falling into a snowball state.

But when that state ended, and the Earth warmed again, the temperature shift may have provided the spark for a more radical change. As the ice sheets melted, the flow of sediments and nutrients they sent into the warming oceans would have allowed life to flourish. Perhaps, some have wondered, the last time this happened it helped spark the Cambrian Explosion, the moment when life rapidly became much more complex.

That, Bisesi says, tipped the scales. As the continents began to be covered in vegetation, they reflected less sunlight. A darker planet absorbed more heat, and that may have been enough to prevent it from ever freezing over again. Once the world turned blue and green, in other words, it may have been just stable enough to stay that way.

Webb Images a Hellish Landscape

A group of astronomers led by Sebastian Zieba of Harvard reported using the James Webb Space Telescope to directly measure the surface of a distant world. Their target, a planet called Kua’kua, lies about fifty light years away. It orbits a red dwarf, a star fainter and cooler than our own, and it is slightly larger than the Earth.

It is not, however, a nice place. Measurements reported in 2019 showed it to be an airless and hot world. Its orbit lies close to its star, and it is tidally locked – which means one side of the planet is forever turned towards the star, while the other perpetually stares out into space. This starward side is extremely hot, soaring to about 1500 degrees Celsius.

Since it has no atmosphere, telescopes like the James Webb can directly measure properties of its surface. Zieba and his team did this, using the telescope to study the rocks and minerals scattered across its terrain. These observations showed it to be a barren place. Its surface is ancient, covered in volcanic regolith, and has likely suffered under billions of years of impacts and stellar radiation.

This means it looks more like Mercury, or perhaps the Moon, than like Earth or Mars. That, given the extreme conditions of Kua’kua, was not unexpected. But other worlds could still offer surprises. The presence of different minerals and rocks can reveal how active a planet’s geology is. And the more dynamic a world is, the more interesting it will be - and the greater the potential for it to host some kind of primitive life.

Psyche Swoops Past Mars

On May 15, NASA’s Psyche probe swung past Mars. The Red Planet is not the spacecraft’s ultimate destination: it is designed to study 16 Psyche, one of the largest asteroids in the belt between Mars and Jupiter. But to get there it needs energy, and it thus used this brief visit to Mars to gain acceleration through a gravitational assist.

Psyche approached Mars from the opposite direction of the Sun. This gave it a view of the planet that we rarely see. In the images it sent back, the Red Planet appears as a crescent, the Sun is almost exactly behind it, and only a sliver of the world is illuminated.

Psyche’s operators used the encounter to test out the instruments and cameras on board the spacecraft. All seems to have gone well, and the team say they captured thousands of observations of Mars. Their next milestone will come in 2029, when Psyche finally reaches its namesake in the asteroid belt.

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The stars are far, almost unimaginably so.

In 1970, as the crew of Apollo 13 fell back towards Earth, they briefly hit a speed of almost twenty-five thousand miles per hour. This is the fastest humans have ever travelled. Even Artemis II, returning from the Moon in April, fell about a thousand miles per hour short of this record.

Had the Apollo 13 capsule been capable of maintaining this speed, it could have looped around the planet in an hour, returned to the Moon in less than half a day, and then gone on to cross the orbit of Mars within a few months. But even at this rate, it would still have taken more than one hundred thousand years to reach Proxima Centauri, the closest star to our own.

As a result, dreams of interstellar travel are often just that. Indeed, there are few technologies that might allow us to span the gulfs of interstellar space. Yet the idea is not completely out of the question. There are a handful of stars within a dozen light-years of Earth. Crossing such a distance is just about feasible, at least according to the team behind Breakthrough Starshot.

They reckon that rather than sending a single big spacecraft, we might be better off sending a swarm of tiny ones. Thousands of these could be launched together. Each would deploy a light-sail, a device that uses the slight pressure of sunlight to create a small but steady acceleration.

This would not normally be fast enough to reach the stars. But Breakthrough Starshot thinks we could accelerate probes faster by using laser beams in place of sunlight. Fire these at small and lightweight spacecraft, they say, and we could get them to a reasonable fraction of the speed of light. Of course such speeds are dangerous - even minor collisions would obliterate a probe - but numbers can compensate for these risks.

To study how such a mission might work in practice, a team led by Marshall Eubanks of Space Initiatives looked at what a swarm of one thousand small spacecraft could do. They imagine accelerating them towards Alpha Centauri at twenty percent of the speed of light. At this rate, they could reach the star system in about twenty-one years.

As they flew through the outer solar system and into interstellar space, however, they would already begin sending back valuable scientific data. At first, they might hunt for planets and dwarf worlds hidden at the edge of the solar system. Later, they could map out the density of interstellar dust, hunt for primordial black holes, and even probe fundamental theories about gravity and about space and time.

The probes would still be travelling at high speed as they reached Alpha Centauri, and would have limited capacity to decelerate. But they would be able to image the planets around the three stars found there, and could look for moons and other objects. Instruments could scan these worlds, image their surfaces, and look for signs of life or other interesting processes.

All this, they conclude, is not only possible to do, but may be the only reasonable prospect for interstellar travel in the coming century. The benefits would be astonishing: swarms could visit half a dozen nearby stars, fly out to rogue planets, and explore the most distant regions of the solar system. But the challenges of making this real should not be understated. At the very least, it will take far more money than anyone has so far seemed willing to venture.

The Clouds of Interstellar Space

Every day, several tons of dust fall upon our planet. Most of it comes from the solar system, in the form of tiny fragments of passing comets, the debris of ancient impacts, and the leftover material from the birth of the planets. But some comes from further afield.

As the solar system moves through the galaxy, it periodically passes through clouds of interstellar dust and gas. About fifteen of these clouds are scattered around us at the moment , and as our system moves through them, it is sweeping up some of the dust they contain.

Bits of this dust eventually make their way to Earth. Although much of it is then simply incorporated into our world, some of it builds up in layers at the bottom of the ocean or in the polar ice sheets. And there, as a recent study found, it can act as a tracer for the history of our star’s long voyage through the galaxy.

The study, led by Dominik Koll of the Australian National University, analysed polar ice formed between forty and eighty thousand years ago. They found that the amount of cosmic dust falling on Earth seem to have increased since that time, possibly because we have recently entered an interstellar cloud.

That would fit well with ideas about our solar system’s recent trajectory. It is currently in the ‘local interstellar cloud’, and probably moved into this cloud sometime in the last hundred thousand years. We are currently heading towards its edge, and at some point in the next few millennia we should enter the nearby ‘G-Cloud’.

Much more work remains to be done. Other sources of dust have been found on the Moon, as well as in oceanic sediments. Together they paint a history of several supernovae erupting in our region of space over the past few million years, and tell a story of how we have moved between the clouds and bubbles sculpted by these violent events.

Getting all of this together into a single cohesive narrative will take time. But once complete, it will reveal the history of our long cosmic journey.

Artemis III

After this year’s successful flight around the Moon, NASA is moving ahead with plans for the third Artemis mission.

Originally, this was supposed to put astronauts on the lunar surface, and would have been the first time anyone had set foot on the Moon in more than five decades. But although NASA now has a rocket and a capsule, it does not have a lander ready to take crews to the surface and back.

NASA was relying on SpaceX to provide this lander. Under contracts awarded in 2020 and 2021, SpaceX was supposed to develop their Starship system to support lunar landings. But progress has been slow, and Starship still isn’t capable of getting anywhere close to the Moon.

With Artemis II complete, NASA has been forced to recognise this reality. Instead of going to the Moon, then, Artemis III will remain in a low orbit around the Earth. To salvage some value from the mission, NASA will practice docking the Orion capsule with Starship. In future missions this step will be crucial, as the two spacecraft are supposed to meet in lunar orbit to allow astronauts to transfer from one vehicle to another.

But in what may be a subtle warning to SpaceX, NASA is also hoping to demonstrate docking with a second lunar lander. This one, being built by Blue Origin, could provide an alternative route to the Moon, and give NASA a backup option if Starship simply is not ready in time.

Saving Swift: A Race Against Time

Since 2004, the orbiting Swift Observatory has been studying the mysterious Gamma Ray Bursts that appear in the distant universe. Although the mission was supposed to last just two years, it is now approaching its twenty-second anniversary in space. In that time, it has carried out more then eight hundred thousand measurements.

Unfortunately, Swift is also on the verge of death. It was originally launched into an orbit six hundred kilometres high, but over the last two decades the atmosphere has dragged it back down. It has now fallen below an altitude of four hundred kilometres and if nothing is done, it will make a fiery re-entry in the next few months.

Last year, however, NASA partnered with a company called Katalyst Space Technologies. Together they have built a spacecraft that could grab Swift and then boost it into a higher orbit. That would save the telescope, and give it another few decades of life.

NASA recently announced this new spacecraft has completed tests on the ground. It will now move towards a launch – possibly as soon as early June – and then start a race against the clock to raise Swift before it falls too low into the atmosphere.

If this works, it would demonstrate an important ability to grasp and raise the orbits of falling satellites. Swift is not the only one of NASA’s telescopes that is in peril of re-entry: Hubble, launched in 1994, is now losing altitude at a rapid rate. If nothing is done, it will burn in the early 2030s. Katalyst’s mission, if it is a success, may offer a way to prolong Hubble into the 2040s and beyond.

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For most of its known history, nobody has cared much about 2002 XV93. It is a small world lying somewhere close to the orbit of Pluto, one presumably covered in a grey and gritty kind of ice, and a place considered so unremarkable that no one has bothered to give it a proper name.

Yet as of last week, 2002 XV93 is suddenly famous. It is, according to a recent discovery, one of the most distant places in the solar system known to host an atmosphere. Truth be told, it is not much of an atmosphere. The small rock measures only a few hundred kilometres across, and the layer of gas surrounding it is at least ten million times more tenuous than the air around our planet.

But that is at least something. And its presence defies our expectations about what the worlds beyond Neptune should look like. All those known to us are icy, frozen objects. Most are small. A few are big enough to be notable: Pluto, for example, was long a member of the exclusive club of planets. Eris is slightly more massive than Pluto, and others – Haumea, Makemake, Sedna – measure more than a thousand kilometres across.

Some of these larger places do have atmospheres. That of Pluto, for example, is a thin layer of nitrogen that appears as a bluish haze stretching over its surface. Traces of methane have been found around Makemake. But others are more elusive. Eris and Sedna, though both large, show no sign of an atmosphere.

That may be because they are much further away – roughly twice as far as Pluto – and thus extremely cold. Any atmospheres these two dwarf planets did possess have surely escaped or condensed into ice. Over the next few centuries, Eris will swing inwards towards the Sun and gently warm. As it does, this ice may sublimate, and the frozen world might regain a thin and temporary atmosphere.

But this should really be the limit. Smaller worlds, those less than about a thousand kilometres across, are not expected to maintain any kind of atmosphere. They lack the gravitational strength to hold on to a layer of gas. If they ever had any, it should thus have long ago escaped into space or frozen to their surfaces.

Yet 2002 XV93 seems to differ. It measures about five hundred kilometres (three hundred miles) across, and so should fall into the category of small, insignificant places unworthy of carrying around a layer of gas. The question is thus twofold. Does it really have an atmosphere? And if it does, how did such a small world manage to keep it?

A Stellar Occultation

The story of 2002 XV93’s atmosphere begins on January 10, 2024. On that day, the small world passed briefly in front of a star in the constellation Auriga, thus creating a kind of mini-eclipse. Astronomers call such events stellar occultations, and they happen whenever a planet or something else in our solar system crosses in front of a more distant star.

Occultations can reveal surprising details about these objects. As a world starts to move across a star, it darkens the light coming from it. If the world lacks an atmosphere, this darkening will be abrupt, caused by the sudden passing of a solid surface between us and the distant star.

But if the body is instead surrounded by gas, the starlight will fade more gradually. The atmosphere may bend and filter the light, changing its colour in response to the gases present there. As the occultation ends, and the world moves on, this pattern will play out in reverse.

Careful study of exactly how the brightness of a star varies during an occultation can thus reveal whether a world has an atmosphere or not. As an example, it was thanks to this technique that astronomers knew Pluto had an atmosphere well before New Horizons arrived and took photographs. By comparing multiple occultations spread over many years, they could even watch this atmosphere expand and contract with the changing seasons.

The 2024 occultation of 2002 XV93 was observed from Japan. A team led by Ko Arimatsu of the National Astronomical Observatory of Japan set up three stations to take measurements of the event. Though they expected to see a sharp pattern, one more resembling that of the airless Eris rather than that of Pluto, the occultation instead showed the brief signs of a layer of gas.

The results, Arimatsu said, came as a surprise. When they analysed the data, they found it showed signs of a thin but clearly present atmosphere. It is tenuous and has a pressure at least five million times lower than that on Earth at sea level. Indeed, to reach a comparable pressure in our atmosphere you would have to ascend hundreds of miles into our faint and rarely visited exosphere.

A World of Ice Volcanoes?

The fact this layer exists at all is hard to explain. 2002 XV93 is so small that even a slight atmosphere should have been lost into space within a few centuries. That we can still see it today suggests something must have recently refilled it, and this tells us this small world is more dynamic than it at first appears.

Some objects beyond Neptune do show signs of atmospheres coming and going. Unlike the Earth, these worlds can follow eccentric paths: Pluto, for example, swings in and out along its long voyage around the Sun. At its closest, it passes within the orbit of Neptune. At its most distant, it is almost twice as far away.

This leads to drastic changes in temperature. Whenever Pluto moves towards the Sun, as it was doing until 1989, it warms up, its ices sublimate, and its atmosphere grows. As it moves away, as it is now doing, it begins to cool again, the gases in the atmosphere condense, and the layer of gas fades away.

Eris, which follows an even more eccentric orbit and is currently much further away, will likely show a similar pattern as it draws closer to the Sun over the next few hundred years. But there is no real sign the same is happening on 2002 XV93: indeed, measurements have found no traces of the kinds of ice on its surface from which an atmosphere could emerge.

Instead, Ko Arimatsu and his team think there are two better possibilities. One is that the world has experienced a recent collision. This would have thrown up a cloud of dust and ice and allowed a temporary atmosphere to form. It will eventually be lost, but it might well stick around for a few decades or centuries.

Alternatively, 2002 XV93 may be home to the phenomenon of cryovolcanism. Though it has a solid and frozen surface, underneath it may have a partially liquid layer. If something is heating this – possibly the tidal force of an unseen satellite, or perhaps a series of small impacts - then this layer could remain liquid. At times, it may be bursting outwards, forming a kind of ice volcano.

We have seen things like this on Pluto. Data sent by New Horizons showed signs of recent eruptions, and its images showed massive features that may have been formed by such volcanic events. We have no clear evidence of anything like this happening on 2002 XV93, but its thin atmosphere offers a hint that volcanoes might be erupting there too.

Whatever the answer is, one thing is clear. The worlds of the outer solar system – from its giants like Pluto and Eris, to its minnows like 2002 XV93 – are far more interesting than they at first appear. They are dynamic worlds, subject to forces and processes so alien and so familiar to us on Earth. They are worthy of attention – and in the case of 2002 XV93, a proper name as well.

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We don’t know for sure what it looked like. Shortly after it was taken, a fire destroyed his laboratory, reducing of his work and early photographs to ashes. But it was enough to prove a point. When the image, and others like it, were shown to French Academy of Sciences, they sparked an excited debate and laid the founding stone of modern astrophotography.

Until that moment, indeed, all astronomy had been done by hand. Since the age of Galileo, astronomers had peered through telescopes and spent painstaking hours sketching what they saw. The results were sometimes beautiful. Galileo’s watercolours of the Moon are impressive both for their simple elegance and for what they revealed about the universe.

Yet, they took time, they invited error, and they relied on the accuracy of the human eye. This was not always to be trusted: Schiaparelli believed he could see artificial lines criss-crossing Mars, the result, he thought, of an advanced engineering project. Others convinced themselves that the Red Planet periodically darkened and lightened, probably, they thought, because plants were growing in the summer and fading in the winter.

In comparison to all this, Daguerre’s technique appeared almost magical. True, it was not the first method of photography: that honour belonged to another Frenchman, Nicéphore Niépce. But Niépce’s process was slow, and sometimes needed a plate to be exposed for days to form an image. Daguerre’s was fast: it could capture an image in seconds.

When the scientists of the French Academy heard what he had done, they were giddy with excitement. Imagine, François Arago said as he announced the work, how this invention could speed up the study of Egyptian hieroglyphics, preserve treasures that would otherwise be lost, and allow the detailed examination of light itself.

For astronomy, the potential seemed great. The camera might, Arago hinted, be the greatest asset to the field since Galileo and his telescope. A revolution had followed that invention, and with Daguerre’s process, science might once again be on the cusp of great and unforeseen discoveries.

Soon after Arago’s speech, the rights to the Daguerreotype process were purchased by the French government. They awarded Daguerre a lifelong pension, elected him as an honorary academician, and later inscribed his name upon the Eiffel Tower. His process was given to the world, published freely, and made available to anyone who wished to use it1.

At the time of the announcement, the American Samuel Morse - he of the telegraph and famous code - happened to be in Paris. He quickly arranged to see the invention in person, and went to meet Daguerre at his residence. The introduction impressed him, and he apparently asked the Frenchman about the possibility of using it to take portraits.

After he returned to the United States, Morse teamed up with a chemist and doctor named John William Draper. The question of portraits still intrigued him, and as an experiment the pair opened a gallery in New York. They charged $5 for a picture - a high sum at the time - yet still attracted many of the city’s elite.

Indeed, the idea quickly proved popular: with a few years everyone from Abraham Lincoln to the Queen of England had posed for the camera. Yet Draper is also remembered for something else: in early March of 1840 he climbed to the roof of New York University, and shot a series of images of the Moon.

Getting it in focus was apparently difficult. Many of the earlier attempts, probably including Daguerre’s lost image, had shown little more than a blur of light against a dark background. But though the details are faint in Draper’s image, the surface of the Moon can be seen, along with its craters, the curves of mountain ranges, and its wide plains or mares.

This is often said to be the oldest surviving photograph of the Moon. There is some debate about that. Draper took many other photos of our satellite, and announced he had succeeded in capturing one several days before this one was taken. But those images have since been lost. This version was likely taken on March 26, 1840, a night upon which the Moon was in its last quarter.

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Where did the comet 3I/Atlas come from?

It was not born in our solar system. Instead, the comet came from the stars: it is passing through our system of planets at high speed, moving so fast that although the Sun has deflected its path, it cannot hold on to the comet. 3I/Atlas will, in the years to come, fly outwards, escape the Sun’s gravity, and then drift on alone through the galaxy for another million years or so.

Based on its trajectory, speed, and direction, astronomers thought 3I/Atlas was probably ancient. It may have come from the halo of stars surrounding the Milky Way. If it did, then the comet could be extremely old indeed, and might have been born around an earlier generation of stars.

At the end of last year, as the comet approached the Sun, astronomers measured the gases streaming off it. Although this showed the object was clearly a comet, it also appeared unlike any other we have seen before. Some of these strange characteristics can be explained by its long and cold voyage through interstellar space. But others are clues pointing to its ultimate origins.

One such clue is the amount of deuterium present in the comet. This is a form of hydrogen. But where normal atoms of hydrogen have a single proton in their nuclei, deuterium atoms have both a proton and a neutron. This makes them heavier than other hydrogen atoms, and subtly influences their chemistry. The ratio of deuterium to hydrogen should be fixed when the comet first forms, and this ratio can thus tell us about the environment in which it was born.

Deuterium is rare. Plenty of hydrogen is present in the Earth’s oceans, especially in the form of water. But for every six thousand atoms of hydrogen in the oceans, there is only one of deuterium. This gives the ratio of deuterium to hydrogen on Earth, and as with the comet, this ratio hints at the origin of our water.

At low temperatures, chemistry tends to favour deuterium over hydrogen when forming water molecules. At higher temperatures, this relationship reverses. This means that when water is created in cold places – for example, at the edge of the young Solar System – it contains a higher fraction of deuterium than that of the gas from which it formed.

This seems to be the case with the Earth’s water. The measured ratio of deuterium to hydrogen is much higher than that found in the primordial material of the solar system. Most likely, then, our water originally formed somewhere very cold – perhaps beyond the orbit of Pluto – and then fell inwards as a long and hard rain of comets and asteroids.

The measurements of 3I/Atlas found an even more extreme case. It has a lot of deuterium, at least forty times the level seen on Earth, and thirty times more than that seen in any other comet. This tells us the comet likely formed somewhere very cold, and probably under very different conditions to those found in our solar system.

But exactly where is still elusive. Astronomers cannot trace its path, at least not for more than a few million years. Comet 3I/Atlas is far older than that. The hints we have, deuterium included, only tell us it came from a very different place, and a very different age, to the one in which we were born.

Big G: Measuring Gravity

In 1797, an Englishman named Henry Cavendish set out to weigh the world.

He did this by suspending a rod from a wire. At each end of the rod he attached small lead balls, and then arranged for a pair of larger spheres to be placed near each. The result was a small deflection in the rod, a twisting motion caused by the slight gravitational attraction between the small and large balls.

By careful measurement, Cavendish was able to calculate the strength of this gravitational force. From this, he could deduce the density of the planet. The result was remarkably accurate: today’s accepted figure is 5.514 g/cm³; Cavendish, at the end of the eighteenth century, found it to be 5.448 g/cm³.

His experiment also gave us a way to measure the strength of gravity itself. Mathematically, this is given by a constant called Big G. It relates the strength of attraction two objects will feel with both their masses and the distances between them. The higher Big G is, the stronger this force will be.

This is a number of immense interest to science. The force of gravity dictates much of the world around us: it determines how fast planets move around their stars, keeps satellites in orbit, and crushes atoms to power the reactions in the core of the Sun. Big G is key to all of this, and the more accurately we can measure it, the better we can understand our world.

Yet doing so is hard. One problem is the weakness of gravity: the deviations it produces are slight, and hard to measure with accuracy. Another is the impossibility of shielding. There is no way to block gravitational influences, and so a passing truck, a nearby herd of sheep, or even a leaf blowing in the wind can all disturb the experiment.

As a result, we don’t know Big G very well. Things have improved since Cavendish’s day, at least slightly, but almost all the other fundamental constants are known with more accuracy. Scientists have tried many ways to change this, but in recent decades experiments have added more confusion than clarity.

The problem is, they find subtly different results. This is probably down to noise, the difficulty of measurement, and other errors. But the overall result is to add uncertainty, especially since we do not always know how big these errors are, and this leaves us in the dark about the true value of Big G.

In an effort to change this, Stephan Schlamminger, a researcher at NIST, dedicated himself to replicating an earlier experiment. If he could get the same answer as they did, then it might settle the question. Unfortunately, he did not. Instead he found several previously unrealised sources of error, and set about removing them.

The result, published in April, was yet another possible value of Big G, in this case, 6.67387x10^-11 meters³/kilogram/second². That doesn’t solve the problem. But it might bring us a little closer. After all, every experiment adds a new data point, and contributes a little to the weight of evidence.

The End of Space Tourism?

A few years ago, it looked as though the long-promised era of space tourism was finally upon us. Two companies – Blue Origin and Virgin Galactic – had begun sending wealthy passengers to the edge of space. Their founders, the billionaires Jeff Bezos and Richard Branson, engaged in an unsightly race to be the first to fly beyond the upper atmosphere. Branson won, but only by a few days.

Since then, Blue Origin has flown seventeen commercial crews beyond the official edge of space. Virgin Galactic has sent seven, each to a slightly lower altitude than Blue Origin. But today, these flights are over.

Blue Origin paused their flights earlier this year. Officially, the company says this is temporary, and it simply wants to devote staff to other projects, including a crewed moon lander. But it also looks unlikely they will resume launches any time soon.

Virgin Galactic, on the other hand, has not flown since 2024. Back then, they retired their spaceplane, and said they were working on a new ‘Delta class’ vehicle. Details have since been limited, but last week they released photos of a new craft outside a hangar.

Virgin Galactic will probably want to fly this spacecraft in at least a few test flights this year. According to the company’s official statements, it should be ready to carry tourists early next year. If it makes it, then the spluttering age of space tourism might get a bit of a boost.

A Hint of New Physics

Over the past decade, researchers at the Large Hadron Collider have been tracking a slight anomaly in the decay of a group of subatomic particles called B mesons.

These particles are formed as the collider smashes together protons. They don’t last for long: within a fraction of a second they decay, or transform, into other particles. There are many possible combinations of particles that can result from this process. But in the one of interest, the B-meson decays into a kaon, a pion, and two muons.

To probe the laws of subatomic physics, researchers study the energies and angles at which particles emerge from collisions like these. The Standard Model of particle physics, our current best understanding of the subatomic world, gives predictions for what should happen.

Yet experiments have persistently shown the reality of this particular B meson decay to differ from these predictions. That could hint at something unknown happening, such at the presence of new types of particles.

But it could also be a statistical fluke. Despite more than a decade of study, the evidence remains weak. Indeed, these kinds of anomaly do occasionally appear, but usually fade away with more data. But, in April, a study found that in this case the more data we get, the stronger the argument seems to become. If that continues to hold true, the B meson could end up being the doorway into a new theory of nature.

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The way NASA tells it, Space Reactor Freedom sounds simple.

This reactor, of course, is a nuclear one. NASA has apparently obtained one, or at least is close to doing so, and has also found a supply of fuel. Fortunately, they also have an electric propulsion system, one they salvaged from a failed project to build a lunar space station. The two, they say, could be bolted together to form a functional spacecraft.

With that done, the whole thing will be fired off to Mars, where it will presumably play a role in spreading Freedom. This is all so easy that the agency thinks it will be ready by the end of 2028, an extraordinary pace for any government program. Afterwards, mission accomplished, Space Reactor Freedom will act as a guide for a future stream of atom-powered probes heading out to the planets.

The catch, however, is that no one has done anything like this before. The United States last launched a nuclear reactor in 1965. It never left Earth orbit, failed after six weeks, and then partially disintegrated fifteen years later. Whatever debris remains is both radioactive and likely to continue circling our planet for the next thousand years or so1.

True, the Soviets did make more serious efforts to develop the technology. Between the 1960s and 1990s, the USSR launched more than two dozen reactors, most of them short test missions. Each was shut down after a few weeks, and they were then boosted into high orbits to allow their radioactivity to decay safely away before re-entry.

Yet in 1977, one of them, a satellite named Kosmos 954, failed within weeks of launch. Finding themselves unable to boost the spacecraft or to jettison its reactor, the Soviets issued secret warnings that the satellite was out of control and falling back to Earth. Four months after launch, it hit the atmosphere over Canada, exploded, and rained radioactive debris across the Northwest Territories.

But even when it worked, the Soviet program restricted itself to niche applications in orbit. No one has ever sent a nuclear reactor into deep space, or sought to unlock the great potential the technology could offer when pushed beyond the Moon.

In many ways, that is a shame. Indeed, space agencies believe that nuclear spacecraft can push aside a lot of the constraints that hold back interplanetary travel. They can go fast, head deep into the Solar System, and carry power-hungry instruments. A nuclear probe could cut the journey time to Mars to mere weeks, carry out a detailed exploration of Saturn or Neptune, and even flit between the icy worlds of the Kuiper Belt.

All we need, if you listen to NASA, is a successful demonstration. And that is what Space Reactor Freedom is all about.

The Reasons To Go Nuclear

To get anywhere in space, you need energy.

Traditionally, this has come from chemical means: rocket engines use various chemicals as fuels, react them to produce gases, and then force them out of a nozzle. The resulting exchange of momentum pushes the spacecraft in the desired direction, rather like a sophisticated balloon carefully releasing its air.

This works, but it can be inefficient. Heavy spacecraft, especially those that head deep into the Solar System, need a lot of energy to propel them. That implies they need to carry a lot of chemical fuel. But the more they carry, the heavier they become; the heavier they get, the more fuel they need. This can quickly turn into a vicious cycle of diminishing returns, one in which every gram of extra fuel simply adds more mass and demands yet more fuel.

Engineers have a few ways around this problem. One is to make use of clever tricks like gravitational assists. These happen when a spacecraft flies past a planet in just the right way to get a kick of momentum, a boost that offers a free acceleration. But they come at the cost of time: Europe’s JUICE mission, for example, is in the midst of a six-year period bouncing between Earth and Venus. Only in 2029, once it has built up enough speed, will it head to its final destination of Jupiter.

A second option is to use more efficient fuels. Hydrogen, for instance, is a good choice: it is lightweight, it reacts strongly and releases plenty of energy, and, in the form of water, it is abundant on Earth. Rocket engines sometimes react it with oxygen, a process that results in hot steam and that can work more efficiently than almost any other chemical engine.

Yet even hydrogen pales in comparison to nuclear fuel. Instead of forging and breaking molecular bonds, nuclear fission splits the atom and unleashes immense energies. A uranium-based reactor produces at least a million times the energy of the hydrogen-oxygen reaction. In spaceflight, where every gram of mass must be carefully accounted for, this is game-changing.

Spacecraft equipped with nuclear engines can avoid the planetary dance taken by missions like JUICE. They can fly direct, and they can take more mass with them. The reactors provide copious power on arrival, and can run day and night. For a rover on Mars, a base on the Moon, or an explorer of Titan, this kind of capability is essential.

The Nuclear Electric Motor

There is no real shortage of ideas of how to make use of this power in space. Indeed, mad scientists have dreamed up a dozen insane variants of the nuclear engine. One concept involved chucking atomic bombs out the back of a spaceship and riding their shock wave out to the stars. In principle it works. In reality this would be impossible to control, hazardous to literally everyone, and a dangerous lunacy to even think about trying.

More sensible is the radioisotope thermoelectric generator. This a device that relies on radioactive decay. It is fuelled by some kind of nuclear material – plutonium-238 is a common choice – and simply uses the heat produced by its decay to generate electricity.

Generators like this are sometimes used for flights into the outer Solar System. Beyond Jupiter, the Sun’s rays fade rapidly, and so solar power cannot keep distant probes running. Radioisotope generators can – and they have been used in missions like Cassini to Saturn, the Voyagers and Pioneers, New Horizons to Pluto and beyond, and on rovers on Mars.

But these are relatively simple nuclear devices, and rarely used for sustained propulsion. Space Reactor Freedom follows an alternative model, that of nuclear electric propulsion. Rather than rely on radioactive decay, it will use a reactor to create a controlled chain reaction. This produces a supply of heat, and that is then converted into a steady current of electrical energy.

The power is then fed into an electrical thrust system. Instead of ejecting gases, these expel charged particles, often in the form of Xenon atoms stripped of an electron, thus creating the desired exchange of momentum. Unlike in chemical rockets, this thrust can be maintained for a long time. Some trials have even produced sustained thrust lasting months at a time.

But until now, electric propulsion in space has always been limited by the power available. Solar is the usual source, and no electric engine has ever exceeded a handful of kilowatts. Nuclear reactors can lift that constraint. They can produce hundreds of kilowatts, even megawatts, and allow the true power of electric propulsion to be unleashed.

A two-hundred-kilowatt electric engine, one ten times more powerful than anything built so far, could send a twenty-ton spacecraft to Jupiter in less than five years. A megawatt reactor, one still easily within the bounds of possibility, could reduce the journey time to Mars to about twelve weeks. More powerful reactors could ship cargo to the moons of Jupiter, to Saturn, and to the very edges of the Solar System.

Space Reactor Freedom

Before all that, NASA needs to demonstrate the concept.

The plans for Space Reactor Freedom are still vague. The details we do have, however, suggest that NASA is prioritising speed over everything else. Nuclear propulsion is not a new idea, they said at a presentation in March, but rather something that has long suffered from poor execution. Over the past six decades, the agency has launched twelve nuclear efforts, yet put nothing more than a single short-lived satellite into orbit.

Their goal is to change this. NASA wants to go fast. They have set a target of launching in 2028, and they want to follow a design based on established technology. Indeed, they think much of the development work is already done, and that the remaining challenge is more about integrating the components than building them.

At the heart of the spacecraft will be a twenty-kilowatt reactor. Details about this are sparse, but NASA boss Jared Isaacman said it was already ‘mostly built’. Yet where it is, and who built it, remain unknown to the public.

This reactor will be mounted on a module originally planned for the Gateway, a space station that was supposed to be placed around the Moon. But that station is now on pause, and the module, which is equipped with electric propulsion systems, could be integrated with a nuclear power source.

Again, details of how this would work are limited, but assuming it can be done, NASA would then have a spacecraft capable of travelling to Mars. Onboard, the agency would put a payload of helicopters, each similar to the small Ingenuity helicopter that flew over the sands of the Red Planet a few years ago.

These helicopters would send back some interesting data, but the science is not really the point of this mission. Instead, Isaacman sees it as a way to prove nuclear technology can work in space. He hopes it would be followed by a series of more powerful missions. These will unlock the full potential of nuclear propulsion, and act, as he puts it, as the ‘transcontinental railroad of the Solar System’.

The deadline of 2028 is still ambitious. Even if the technology is already there, anything nuclear will face regulatory hurdles. The reactor will need to be safe – an accident could be fatal to the dream – and ensuring that will take time. So will the steps of making sure the design actually works. But Isaacman is still right to challenge NASA to move fast.

Indeed, the future direction of space exploration may rest on his success. If the reactor flies – whether that is in 2028 or in the early 2030s – it should inspire future missions to Mars, to Jupiter, and beyond. The road ahead is surely more challenging than NASA will admit now, but once the tech is in place and proven, then the outer Solar System awaits.

After travelling further into space than any human before them, the crew of Artemis II returned safely to Earth on April 10th.

Their voyage lasted ten days, and covered a distance of almost seven hundred thousand miles. At their apex, they were more than a quarter of a million miles from Earth. As they passed over the Moon, they ventured closer to our natural satellite than anyone since 1972.

The moment of greatest peril, though, came in the final minutes of their mission. Their Orion capsule, named Integrity by the crew, hit the outer atmosphere at a speed greater than twenty-four thousand miles per hour. Humans have rarely travelled this fast. Only the Apollo missions, as they too returned from the Moon, have reached similar speeds.

Before launch, some concern had been raised about the ability of the capsule’s heat shield to protect the crew from the dangers of re-entry. In Artemis I, the uncrewed first test flight, this shield did not perform as expected. Later analysis showed it had been damaged during its plunge through the atmosphere.

In an effort to avoid a repeat, NASA engineers redesigned the trajectory the capsule follows during re-entry. They also tested the heat shield on the ground – though, of course, nothing we can do in a lab is able to recreate the reality of falling through the atmosphere at thirty-five times the speed of sound.

Fortunately, the shield seems to have performed as expected. Images taken of it after splashdown appear to show it in good condition, with little of the charring and erosion seen after Artemis I. That is good news. More work, of course, is needed. NASA will now study all the data obtained - including from observation aircraft - and subject the shield to a series of tests to better understand how it behaved.

As they do this, however, attention will surely turn to Artemis III. Until recently, this mission was supposed to take humans to the lunar surface for the first time in decades. For this, NASA was relying on SpaceX to provide a lander in the form of Starship. But progress has been much slower than hoped, and Starship simply won’t be ready to support a landing in time.

Instead, Artemis III will now remain in Earth orbit. Instead of going to the Moon, astronauts will practice docking with the lander. If SpaceX can get Starship into orbit and show sufficient control for a safe approach, the Orion capsule should dock with Starship. That would prove the technical ability of both vehicles to work together. But it would also allow operators and astronauts to get experience in what promises to be a challenging operation.

NASA has also introduced a bit of competition. Blue Origin has been working on its own lunar lander, which Orion could, if the lander is launched in time, use as a docking target as well. That, if successful, would give NASA an alternative way to reach the Moon before the decade is out.

The Darkening Waves of Mars

Until the 1960s, astronomers were convinced that the surface of Mars was periodically swept by ‘waves of darkening’. These would come and go with the seasons, and would spread from the polar regions towards the equator. Nobody knew what was causing these waves, but most theories held that they were somehow linked to seasonal shifts on the red planet.

A paper from 1966 paper summarised the two most common explanations. The first, and favourite, held that the warmth of the Martian spring was melting the polar caps and putting moisture into the air. This sparked waves of plant growth, which from Earth we saw as a wave of darkness spreading around the planet.

The other, more boring suggestion argued that seasonal changes in temperature caused wind patterns to shift. These winds would at times blow clouds of dust off the surface, revealing darker underlying rocks. When winds calmed, the dust would settle and Mars would seem to become brighter again.

When spacecraft first arrived at Mars, it became clear that the first theory was utterly wrong. The Red Planet does not have plant life, and it does not show a seasonal shift in colour as vegetation grows and dies. Indeed, since the dawn of Martian exploration, we have barely noticed any kind of annual change in the colours of Mars.

Yet, over a longer scale, Mars’ surface does show some shifts in colour. Mars’ Utopia Planitia – a vast basin that may once have held a small sea – has gradually become much darker over the past few decades.

A comparison of photographs taken by NASA’s Viking orbiter in 1976 and by ESA’s Mars Express in 2024 shows this change clearly. Places that were once tan in colour are now black, and this darkness seems to be spreading.

Researchers do not know for sure why this is happening. But it is probably caused by dust blowing in Mars’ thin air. Either, ESA says, black volcanic ash is being blown by the wind and covering tan areas with darker material; or winds are blowing tan dust off previously covered areas, and so revealing the underlying darker rocks.

Voyager

After travelling for almost half a century, the Voyager 1 probe now lies more than twenty-five billion kilometres from Earth. It is the most distant man-made object in the universe, and, remarkably, it is still sending data back to us.

Voyager owes this longevity in part to the nuclear batteries that supply it with energy. These are based on a core of plutonium, and convert its radioactive decay into electrical power. But over time the plutonium is decaying, and as it does, the power generated is also decreasing. This will eventually mean the end of Voyager. Sometime in the coming years the power output will fall below the level needed to operate its radios, and contact with the probe will be lost.

Until that moment, however, operators are doing what they can to keep the spacecraft running. NASA has developed a plan for switching off Voyager’s scientific instruments one by one, a process that balances the risk of running short of power with the desire to return valuable data for as long as possible.

At the end of February, however, operators noticed a sudden drop in Voyager’s power output. Out of caution, they decided to switch off a device called the LCEP, an instrument that measures levels of charged particles around the probe.

Only two other scientific devices remain operational on Voyager 1. NASA has plans to reconfigure all of Voyager’s electrical systems sometime next year, which they hope will cut power use and extend the remaining life of the probe. It might even, NASA said, allow mission control to turn the LCEP back on.

Are Quarks Fundamental?

Until 1899, physicists thought atoms were the fundamental building blocks of nature. Their name reflects that: the word atom comes from the Greek atomos, meaning ‘indivisible’. But then J. J. Thomson discovered the electron, and the search for fundamental particles shifted to the next level down: the world of electrons, protons, and neutrons.

Later, in the 1960s, physicists realised yet another layer existed. Protons and neutrons, it turned out, were not fundamental, but were made from quarks. Today, this is where things remain: all atoms, as far as we know, are made from various arrangements of quarks and electrons.

Might there still be another level down? At the Large Hadron Collider at CERN in Switzerland, researchers have probed the structure of the quark to see if it, too, is made of some more fundamental particle.

These experiments collide protons at high speeds. In the aftermath of these impacts, the proton breaks apart into quarks. By studying how these quarks move, physicists can work out whether they act as point-like particles, or whether they have some internal structure.

In a paper published recently, researchers said these experiments have found no signs of any deeper layer of nature. Quarks appear to be point-like, or at least smaller in size than one hundred billionth of a nanometre.

Upgrades to the Large Hadron Collider should soon allow researchers to probe even smaller scales of nature. If there is another layer at the bottom, those experiments may soon spot hints of its presence.

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In March, a chunk of rock and metal appeared over Lake Erie, flew at supersonic speed over northern Ohio, and then blew up in a deafening explosion. Over the next week, at least four other fireballs appeared over North America: one above Texas, two over California, and one that flew across Michigan. None caused any significant damage on the ground, but all were seen and heard by hundreds of people.

This surge of bright meteors did not just hit America. In Europe, an object flew at speed over Luxembourg and Germany on March 8, exploded just before it reached the Rhine, and sent a fragment of rock into someone’s bedroom. A few days later, another bright fireball was seen above France, this time heading towards the border with Spain.

Is something unusual going on? Such a spate of fireballs seems out of the ordinary. And statistics seem to back up the idea that something has changed. According to the American Meteor Society, there were more big meteor strikes in the first quarter of 2026 than in any other recent year.

Most of this increase – the numbers for which are based on witness reports – came in the month of March. Although reports in January and February were slightly higher than normal, the Meteor Society says, it was only towards the end of February that they really started to pick up.

This may partially be explained by a seasonal pattern in appearances. For reasons that aren’t entirely clear, the number of fireballs tends to increase during the spring months of the Northern Hemisphere. Possibly, NASA says, a patch of debris happens to lie in the part of the solar system we traverse at that time of the year.

But it may also be something to do with the solar antiapex, the point in the sky away from which the Sun is travelling. In the spring months this point reaches a zenith in the northern sky, and this seems to be linked to a peak in the number of meteors we see here on Earth.

The real difference, according to the Meteor Society data, is not just the number of meteors seen, but their size. The strikes that came this year seem to have been bigger than average, and large enough to punch deep into the atmosphere and explode with a loud boom.

The Origins of a Fireball

Despite some patterns in how their numbers vary over the year, meteors can come from any direction at any time. All are lumps of rock or ice that were, until they encountered our planet, drifting quietly through the solar system. Most are tiny. Every day about ten metric tons of dust falls upon our world, but others are larger, measuring anything from a few centimetres across to several metres.

Whenever one of these objects draws too close to the Earth, it begins to fall. Since the Earth’s gravitational field extends far into space, anything that encounters the outer atmosphere will already have been accelerating towards the planet for some time. The force of this attraction means it must hit those outer layers of air at a speed greater than twenty-four thousand miles per hour.

At this immense speed, air molecules cannot get out of the way of the incoming meteor. Instead they begin to pile up, forming a region of increasing air pressure directly in front of its passage. As pressure increases, so does temperature, and soon all that heat begins to eat away at the rock and ice.

Small objects disintegrate rapidly. But big ones can survive the initial heat and begin to punch through the thicker, lower layers of the atmosphere. As they do, hot air begins to break into the interior of the rock, starts to attack its internal structure, and eventually rips the object apart. When the end comes, it is sudden. The kinetic energy of the meteor is converted into heat, and it detonates with force.

The result is a hot shock wave. Witnesses to big meteor fireballs – those in Chelyabinsk in 2013, or that in Tunguska in 1908, for example – described flashes of light as bright as the Sun and a wave of intense heat. Some were burned, as if they had stood in bright sunlight for many hours.

The event in Ohio released energy equivalent to almost four hundred tonnes of TNT. The meteor over Chelyabinsk exploded with the force of half a megaton of TNT – dozens of times more powerful than the nuclear explosion in Hiroshima. Tunguska, in 1908, released more than ten megatons, the equivalent of a large thermonuclear bomb.

Is Something Going On?

Fortunately, these kinds of big impact are rare. Events like Tunguska – probably caused by an asteroid or comet measuring about fifty metres across – happen only once every few centuries. Meteors like Chelyabinsk – twenty metres across – arrive once every few decades.

The Earth is big, and most of it is empty. When a big strike does happen, it is far more likely to be over some remote region than over a metropolis. Last year, one of the biggest fireballs occurred over the Pacific Ocean, some four hundred and fifty nautical miles south-west of Mexico. Another exploded over the central Indian Ocean, eight hundred nautical miles south of India.

Both of these events were much bigger than those seen over Ohio or Luxembourg earlier this year, but since there were very few people around to see them, they passed almost entirely without comment. In many cases, indeed, these fireballs are spotted not by people, but by radar systems or by satellites looking for lightning strikes. But these methods are imperfect, and many impacts, even quite big ones, probably pass entirely unnoticed.

This, then, is the main reason why the early part of 2026 has seen an uptick in fireball numbers. By random chance, more strikes have happened over populated areas, and in an age where cameras are now everywhere, more people have captured footage of them streaking through the sky. This randomness probably also explains why this year’s meteors have been larger and more obvious than usual.

Indeed, in the longer run, this year is unlikely to look like much of an outlier. Meteors have always hit the Earth, and people throughout recorded history have reported the occasional flash of light and rain of stones coming from the sky. They rarely hurt people, and those that are big enough to do so are fortunately rare and more likely to explode over the oceans than over land.

This year’s spike in fireballs is nothing to worry about. Instead, if you see one, appreciate you are almost certainly witnessing the demise of an ancient piece of the solar system, one that had survived for billions of years, until it happened to fall upon our blue world.

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For the first time in half a century, humans have flown over the surface of the Moon.

The moment of closest approach came on Monday evening. After flying for six days, the Orion capsule came within four thousand miles of the surface. From inside the capsule, astronauts were able to view the face of the far side of the Moon, and so observed, NASA said, parts of the lunar surface that had never before been seen directly by human eyes.

Shortly before this close approach, the Orion capsule passed a symbolic milestone by becoming the first crewed vehicle to travel more than a quarter of a million miles from Earth. The astronauts on board Orion thus became the most distant travellers from our planet in all of history.

As they broke this record, Jeremy Hansen – the Canadian astronaut on Orion – paid tribute to the ‘extraordinary efforts and feats’ of their predecessors in space exploration. It would, he hoped, be a short-lived record, one that the next generation of explorers should take it upon themselves to far exceed.

While they passed over the Moon, the astronauts studied the lunar surface and relayed comments back to scientists on Earth. Briefly they also experienced a remarkable solar eclipse, during which they were able to see the solar corona extending around the Moon and observe flashes of small meteorites hitting its surface.

Overall, the mission has gone better than most people had expected. The launch, on April 1, came within minutes of the launch window opening and placed Orion almost exactly where mission planners had targeted. The capsule itself has performed well, and aside from a few problems with the onboard toilets – not, sadly, uncommon during spaceflight – the life support systems have apparently functioned well.

Engineers did notice issues with helium leaking from propulsion systems at a higher than expected rate. This helium is used to keep the spacecraft’s fuel at the correct pressure, and is normally confined by a set of valves. Though the leak is not an issue for the success of Artemis II, it will likely trigger a redesign for future versions of the capsule.

The next big challenge will be the re-entry. Orion will hit the upper atmosphere at twenty-four thousand miles per hour. It will need to lose almost all that speed in less than fifteen minutes, during which time the capsule will be exposed to a furious heat and pressure. To keep the crew safe, Orion is fitted with a heat shield.

Yet this shield has been a matter of some controversy. During the previous flight of Orion, the shield did not behave as expected. Engineers thus modified the re-entry trajectory of Orion to try to avoid any risk – but this does mean the crew are relying on a shield that has not been fully tested and that may not perform as well as it should.

The risk to the crew, NASA said, is low. But all will no doubt be breathing a sigh of relief as soon as Orion is spotted descending gently towards the waves under a canopy of parachutes.

Ignition For a New Golden Age?

After Artemis II, what comes next?

At an event at the end of March, NASA laid out an ambitious vision of its future. Key to this is a series of planned missions to the Moon, together involving robotic explorers, crews of astronauts, and the building of a lunar base. But NASA also wants to build nuclear-powered spacecraft and find a new future for the International Space Station.

Under the new timeline, the next Artemis mission will launch in 2027. It will not go to the Moon, but will instead stay in orbit around the Earth. NASA will use the mission to practice docking with the proposed landers – one, Starship, built by SpaceX, and the other, Blue Moon, built by Blue Origin.

This, NASA boss Jared Isaacman says, will be followed by two missions to the lunar surface in 2028. Both will take crews to the surface, and will be the first of a long series of missions taking place every six months. Alongside these, NASA will send twenty robotic missions to the Moon, including the previously cancelled VIPER rover.

NASA’s Artemis plans had, until now, included a lunar space station called the Gateway. Work on this was proceeding slowly, and it was unlikely to be built until the 2030s. NASA has now called time on it. In place of the Gateway, Isaacman wants to direct efforts towards building a lunar base. It is this project that will be supported by many of the crewed and robotic missions he foresees over the next decade.

Closer to home, NASA has also rethought the future of the ISS. At the moment this is supposed to be retired sometime in the early 2030s. But Isaacman now proposes attaching a new module to the station. This – a core module – will contain the key functions needed to support a space station.

Commercial partners could attach their own modules to it, allowing NASA to build a kind of hybrid commercial station. But it also seems possible the module will help extend the life of the station, and perhaps make it less reliant on the Russian segment. The end result could be an extension of the ISS, or at least a core that could support a new, smaller station in the future.

All this is exciting. But it is also expensive, and far from fully funded. Congress will need to approve the plans and agree to pay for them. That, in a week when President Trump proposed cutting NASA’s budget by a quarter, promises to be the biggest challenge of all.

Hubble Watches A Comet Die

A year ago, astronomers spotted a comet heading towards the inner solar system. It was named C/2025 K1, and measurements of its orbit soon showed that it was probably a fresh comet, one that had fallen from the distant Oort Cloud and that had never before passed close to the Sun.

Despite its size – the comet measures about five miles across – astronomers thought it was unlikely to survive its encounter with our star. Indeed, at its closest the comet passed closer to the Sun than the orbit of Mercury, and the heat of this close approach placed immense strain on the icy object.

About a month after the comet had passed the Sun, the Hubble telescope captured some images of it. They show the comet breaking up – instead of a single lump of ice, several large fragments were visible. These fragments were not themselves stable. Indeed, even as Hubble watched, one of them broke apart into several smaller pieces.

Thanks to Hubble’s images, astronomers were able to trace back the timeline of just how the comet had disintegrated. Each event in its break-up exposed fresh, pristine ice from its interior, and astronomers now hope to study how this ice behaves as it is exposed to sunlight for the first time.

The surviving fragments of the comet are now heading back towards the outer solar system. A million years from now they may exit it entirely, and then go on to drift through interstellar space. But at least one fragment might remain bound to the Sun. If it does, it may yet return to the inner solar system one day in the far distant future.

A Flood of New Asteroids

Astronomers working at the Vera Rubin Observatory in Chile announced the telescope had discovered over eleven thousand new asteroids. This haul came even though the observatory has not yet started its main mission, and was based on observations taken during work to optimise its performance.

Among the thousands of new asteroids are thirty-three Near-Earth Objects. As these can potentially threaten Earth – one need measure only a few metres across to cause an impact – astronomers are keen to find and track as many as possible. Fortunately, none of those spotted by Rubin are likely to hit Earth any time soon.

Looking further out, Rubin also saw hundreds of comets and asteroids lying beyond the orbit of Neptune. Only about five thousand such objects are currently known. With the aid of Rubin, astronomers hope to increase that number at least tenfold in the next few years.

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Unfortunately, the American moths he tried proved unsuitable. They were susceptible to disease, and none could produce silk fast enough to make commercial sense. But Trouvelot thought he had a solution to this too. A hardier species of moth, he reckoned, could be bred by importing the gypsy moth from his native France.

By 1868, he had acquired some eggs and started rearing them on his farm in Massachusetts. Unfortunately, the next year there was a sudden storm, his caterpillars were blown into a nearby woodland, and soon they began to multiply.

Within a few decades of that fateful night, the gypsy moth was everywhere. Today, its caterpillars consume a million acres of foliage every year and cost the economy about a billion dollars annually in lost timber. Efforts at eradicating them have mostly proved unsuccessful.

Trouvelot abandoned his silk farming efforts some time after that disaster. Instead he turned his mind towards art and astronomy. At first, it seems to have been a hobby: he sketched the aurora and a meteor shower. But eventually his work was seen by astronomers at Harvard, and they invited him to make use of their great telescopes.

This was a time before photography was widespread. Early efforts at photographing the stars in the 1840s had used daguerreotypes, but they had proved unsuitable for anything but the brightest objects. By the 1880s, astronomers had photographed the Moon and the Sun and precious little else.

Recording observations was thus mostly done by hand, and this was the art at which Trouvelot excelled. He made over seven thousand astronomical sketches. He drew stars and nebulae, the planets, the rings of Saturn, and the appearance, in 1881, of a comet.

In 1876, some of his sketches were displayed in Philadelphia as part of America’s Centennial celebrations. After this, he set to work preparing a book of his work, and though he had returned to Paris before it was in print, this book - The Trouvelot Astronomical Drawings Manual - was published in 1882. The drawings below are taken from that work, and were made in pastel.

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The hottest stars are blue. These are the beasts of the galaxy, massive stars that can be seen from incredible distance. But they do not live long: they burn their fuel furiously, and die young. Scattered all around them, and far outnumbering them, are smaller, redder stars. These, the red dwarfs, are almost immortal. They burn their fuel so slowly that they will endure for trillions of years to come, and will only face death in that future epoch when the cosmos begins to fade into darkness.

Somewhere between these two extremes lie stars like our Sun. It is a G-type star, a class that puts it alongside stars like Alpha Centauri, Tau Ceti, and 51 Pegasi. These stars are not especially big or bright, though they are considered to be stable and most will survive for about ten billion years before they run short on fuel.

Studying other G-type stars can tell us about the past and future of our Sun. Those that are most like our Sun – especially in terms of mass, colour, and chemical makeup – are known as solar twins. Though they were probably not born together with our star, they will follow a similar path through life.

Until recently, only a dozen or so solar twins were known. But thanks to the Gaia Space Telescope, we now have a map charting the positions and properties of more than a billion stars in the Milky Way. By searching this map, a team of researchers based in Japan and France say they have identified more than six thousand solar twins.

Each burns with a temperature within two hundred degrees of that of our Sun. Each also has a similar surface gravity, a detail which implies they have more or less the same mass and density. And each is made of a similar set of chemical elements, and so emits light with the same characteristics as our star does.

This catalogue has a lot of potential. If we know where the solar twins are, we can watch them and see how they behave. This can offer insight into rare events: for example, there are hints that the Sun occasionally unleashes gigantic flares. Since this happens once every few hundred years, our odds of catching one are small. But if we can watch many Sun-like stars, those odds suddenly become far better.

It can also allow us to trace the history of the galaxy and of our solar system. Analysis of the ages of these solar twins shows two separate groups. One is relatively young, and formed about two billion years ago. But the other is older, and matches the age of the Sun: these stars formed between four and six billion years ago.

Many of the stars in this second group appeared to have moved outwards from the centre of the galaxy. The Sun was probably part of this vast stellar migration: it seems to have formed about ten thousand light-years closer to the galactic core than its current distance, and then drifted outwards at some point.

The reasons why this migration took place are still unknown. But the researchers behind the analysis suspect it has something to do with the bar that stretches across the centre of the Milky Way. The formation of this bar could have sparked the birth of new stars, they say, including our own. Afterwards, its presence could have helped push these new stars outwards.

The centre of the galaxy is probably hostile to life: it is crowded, chaotic, and often hit by powerful events like supernovae. Our star’s outward migration brought it into a calmer neighbourhood. We might owe our very existence to that long-ago voyage across the galaxy.

The Great Silence in The Heavens

It has been almost one hundred and twenty years since the first human words were transmitted by radio. In theory, those words – a short speech, a song, and a wish for a Merry Christmas – are still out there somewhere, marking the forefront of a bubble of sound coming from our planet. In practice, of course, that early signal is now so distant and dilute that even the most sensitive receiver would have trouble hearing it.

Yet the idea remains. Our radio signals have been leaking out into space for more than a century, and anyone out there listening could pick up the sounds of our world. The same may be true in reverse: one day we could pick up a radio message coming from another intelligence, another civilization out there in the stars.

This formed the basis for SETI, a long search for artificial radio signals coming from space. But, despite a decades-long hunt, this search has found nothing. There appears to be a Great Silence in the heavens, a dearth of noise that makes some wonder if we are alone.

But there may, according to a new paper, be a good reason for this silence. It points out that any radio signal leaving Earth must first pass through a region of space shaped by the Sun. This can be a turbulent place: it has shifting magnetic fields, the everlasting solar wind, and the occasional passage of a big solar storm. All this alters the radio signals passing through it.

The result, the authors say, is a broadening of narrow radio signals. Those focused around a single frequency – as artificial ones tend to be – will be weakened, and the ratio of signal to noise will fall. Any observer would then struggle to distinguish these signals from natural ones.

This is not just a theoretical possibility. The study also looked at the radio signals coming from distant probes, including those sent by Pioneer and Voyager. All showed signs of distortion, and saw this worsen when the Sun was more active than normal.

Such effects do not make it impossible to detect radio signals coming from other star systems. But it does mean we might have been looking for the wrong thing – and that by modifying our search parameters, we might stand a better chance of spotting the long-sought-after message from the stars.

A Charming Proton

Every atom is made of a collection of quarks and electrons. The electrons fly alone, forming a hazy cloud around a central nucleus. The quarks cluster in this nucleus, and combine to form protons and neutrons.

There are six kinds of quark, though only two of them – the up and down quarks – appear in atoms. Protons are made of a group of two up quarks and a single down quark; neutrons are the reverse, containing a single up paired with two downs.

The other kinds of quark – the charm, the strange, the top, and the bottom – are seen more rarely. Indeed, the last of them, the top quark, was only discovered in 1995. But as with the up and down quarks, these can also combine into larger particles. When these particles contain three quarks, as protons and neutrons do, they are called baryons.

About eighty such baryons are now known. But almost all are still dominated by up or down quarks, and have only one of the more exotic flavours. Last week, however, CERN announced the discovery of a new baryon, one made of two charm quarks and one down quark.

This makes it look something like a proton, just with the up quarks replaced by the heavier charms. The discovery was not unexpected – its existence is allowed for by the known laws of physics, although it is not thought to be particularly stable. But this is at least an opportunity to study another particle, and to see if it acts as our laws of physics say it should.

Nucleobases on Asteroids

Last week, researchers announced they had found all the essential components of DNA in a sample brought back from the asteroid Ryugu. This includes the five nucleobases found in all DNA and RNA molecules, each of which is thought to have played a key role in the origins of life on Earth.

These kinds of molecules have been found on asteroids before – samples of Bennu collected by Osiris-REx contained some of them, as did some meteorites that were examined after they fell to Earth. This discovery is not therefore something completely new, but it does strengthen the picture we already had.

Because these molecules seem to be widespread on asteroids, it suggests they can form easily through chemical reactions taking place in space. After the Earth formed, it may have been impacts of asteroids like Ryugu that brought the ingredients of life to our planet. And if that was the case here, it should have been the same on many other worlds.

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Yet every now and then, astronomers notice that a big star has simply vanished. This is quite remarkable. Rather than exploding, it would be as if Betelgeuse switched off one day and calmly blinked out of existence. Instead of shining with the light of a billion suns, it would quietly cease to be.

These disappearances are hard to spot. Unlike supernovae, which are bright and all but impossible to miss, vanishing stars don’t announce themselves. We spot them only by chance, usually when astronomers happen to notice that a bright star is no longer shining where it once did.

One such case came in 2024, when researchers realised a bright star in the Andromeda Galaxy had disappeared. There was no supernova, and instead only a faint glow coming from the place where this star used to lie. A decade earlier it had seemed to be a yellow supergiant, one on the verge of a dramatic death. Yet despite a small flare-up in 2014, nothing else of note has been seen since. The star seems to have quietly faded away.

The only other convincing example was spotted in 2015. It, as before, seems to have been a supergiant star, probably one twenty-five times the mass of the Sun. In 2009 it brightened, but in the years after it too faded away without a supernova. Today it is gone. Like the more recent example, the star seems to have silently slipped away into retirement.

Where are these giant stars going? That they have quietly turned off seems hard to believe, if not physically impossible. Without the radiation pressure coming from within, these stars would collapse. And that implosion should trigger a shock wave that must blow the star apart. A supernova, according to our current understanding of dying stars, would be inevitable.

But there is a possibility they are directly collapsing into black holes. Some theorists think that in a big enough star, one with a compact core, the shock wave could stall. If this happens, the centre of the star forms a black hole. The outer layers are sucked in, and whatever remains slowly fades away. No supernova takes place, and, if one is watching from a distance, the star quietly seems to vanish.

The Problem With Red Supergiants

The fate of a star depends on its mass. Those the size of our Sun will, after a few billion years of life, swell up into red giants, gradually shed their outer layers, and slowly fade into darkness. This happens because they are powered by fusing hydrogen, and when this hydrogen starts to run out they begin to cool and expand, and then – once this process reaches an end – gradually dim.

But when a star is above about eight solar masses, another process kicks in. These stars are big enough to fuse heavier elements, and they can burn helium and carbon, and other elements up the periodic table until they reach iron. Iron is not well-suited for nuclear fusion: the reaction takes in more energy than it releases, and when a star reaches this point, the end is not far off.

But before that, the star expands. As it begins to fuse helium, it swells into a red supergiant – a bubbling cauldron of a star similar to the current state of Betelgeuse or Antares A. The most massive stars can briefly become yellow supergiants. These are extremely bright, very unstable, and rare – indeed, only a few dozen of them are known in the Milky Way.

All big stars become a delicate balancing act. On one side they are massive, and all that mass tries to fall inwards and compress the star. But this force sustains immense nuclear reactions in their cores, and this creates a pressure that pushes out and tries to expand the star. The more a star compresses, the more furious the nuclear reactions become, and the stronger the expansion pressure that results.

This can sometimes result in pulsing stars, in which the balancing forces oscillate. At times gravity seems to be winning the battle, and the star shrinks. But this triggers a response from the core, and strengthens the opposing pressure. The star brightens, and then expands again. This cycle can repeat over and over, following patterns that last many years at a time.

Eventually, gravity always wins. At some point, the core of the star fills with iron, the nuclear reactions slow, and the internal pressure stops. The outer layers implode at enormous speed, crash into the core, and trigger a powerful shock wave. This blows the star apart. The inner core collapses, forming a black hole or neutron star, and around it a supernova detonates.

When we spot the flash of light this creates, astronomers swing into action. We cannot yet predict exactly when a giant star might explode. But we do have automated telescopes that detect them almost as soon as they appear. Astronomers then look back at previous observations to work out which star exploded – this is called the progenitor star.

Progenitors are valuable, since they can sometimes tell us what a star was doing in its final years. Yet these studies have raised an odd puzzle: though red supergiants range in mass from eight to twenty-five solar masses, almost all the ones seen to explode are smaller than about twenty solar masses.

The biggest stars, it appears, do not die as they should. This is known as the red supergiant problem.

Failed Supernova and Dust Clouds

Are the biggest stars simply vanishing? If they collapse directly into black holes, with no corresponding supernova, it stands to reason we would not find any progenitors bigger than about twenty solar masses. Above this point the core might become compact enough, the shock waves could stall, and the whole thing could be swallowed by a fast-forming black hole.

Yet, this should still leave some signs. As the debris of the dead star circles the black hole, it should release a lot of energy. We ought to see x-rays flaring out, and this should mark the spot where the star once stood. But surveys have not found any clear signs of this actually happening.

Neither have efforts to monitor big stars revealed much. In one study, astronomers watched millions of big red supergiants over more than a decade. Almost all of them were still there by the end, and only one disappeared in a way that could hint at direct collapse into a black hole. And even in that case, the x-ray signature was missing, and still is, more than a decade after the vanishing act.

Some astronomers wonder if there is something more complicated going on. It could be that red supergiants shed mass before they die. Strong winds blow from within them, and these send clouds of gas streaming out into space. Eruptions can sometimes eject big chunks of stellar material – something like this seems to have happened to Betelgeuse in recent years.

This could create two effects. One is that the biggest stars might shrink drastically before they die. If they lose mass fast enough, then all progenitors might be expected to be below some upper limit, just as observations have seen. But second, is that the dust and gas they expel could make them look fainter than they really are.

If this is the case, then it may confound our measurements. Astronomers normally assume a bigger star shines more brightly than a small one. But if big stars on the verge of death happen to be dusty, then they will be darker, and astronomers will think they are smaller than they really are. Big progenitors could be missing simply because we don’t detect them properly.

As for the two stars that we thought we saw vanish, there might be another story that fits the facts. Emma Beasor, an astronomer based in Liverpool, England, thinks these are better explained as collisions between stars, rather than collapsing ones. In the years leading up to the collision, the two stars would look like a single very bright one. The collision itself would cause a flare, and then in the years afterwards the resulting object would darken, and possibly be surrounded by dust.

There is, then, no shortage of possibilities. The idea that giant stars might collapse directly into black holes is a neat solution, and a seductive one, but we need more data to understand if it is right or not. But even if it turns out to be wrong, the search will still reveal the workings of some of the most violent events in the cosmos.

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Of all the known stars, WOH G64 is surely one of the most extreme. It is enormous. Were it placed at the centre of the solar system, it would consume all the planets out to the orbit of Jupiter. If it were instead at the distance of Alpha Centauri, it would shine in the sky almost as brightly as the full moon. Even across such a span of space, its light would still be strong enough to cast shadows at night.

Such big stars do not live long. WOH G64 is probably about five million years old. Some time in the past few hundred thousand years it became a red supergiant: that is, it ran short of hydrogen fuel, switched to burning heavier elements such as helium, and swelled to its present brobdingnagian size.

Over the last decade, however, it seems to have undergone another change. Around 2011, the star started to dim. It then reversed course, and dramatically brightened between 2013 and 2014. At the same time, it became hotter, shrank, and changed colour, shifting from red to yellow.

That was a potentially significant change. Very big stars like this one can sometimes evolve into what astronomers call a yellow supergiant. These are rare: in our galaxy there are only about two dozen of them. Partly this is because big stars are uncommon. But it is also because they don’t live long – yellow supergiants are hot, bright, and highly unstable.

Yet over the past year, WOH G64 seems to have calmed down. It has cooled, and its colour has shifted back to a more reddish hue. It has also become less bright, and might have once again swelled in size. If it was a yellow supergiant, it doesn’t seem to have been one for long.

In an attempt to understand what is going on, Gonzalo Muñoz-Sanchez at the University of Athens has studied the data we have on this star. He reckons we might have been fooled in the past. Instead of a single star, he says, we might be looking at a binary system in which a small hidden star is orbiting a much larger giant.

These two stars are close, and this means the smaller one can pull material out from the larger one. That could be creating a thick blanket of gas around the partners, something that might glow red and look rather like a vast red supergiant. But at times – and this may have happened over the past two decades – some kind of disturbance may hit this blanket.

When that happens, the true nature of the star is revealed to our telescopes. In the place of a vast supergiant, we see a smaller and yellower star. Its brightness fluctuates as its partner moves around it, and for a few years the star thus seems to radically alter in nature. Afterwards, as the gas blanket recovers, the system goes back to its previous reddish appearance.

Astronomers are uncertain about what the future holds for this system. It is certainly dying. Within the next few thousand years it might explode in a dramatic supernova. That, since the aftermath would be easily visible to the naked eye, would be a spectacular event. But it is also possible that a stranger fate might await it: one day the star might simply vanish, and implode silently into a black hole.

NASA Rethinks Artemis

NASA has shaken up its approach for returning to the Moon. The move comes at the behest of Jared Isaacman, the newly appointed head of NASA, who is keen to reform and accelerate the work of the space agency.

He has identified NASA’s moon rocket, the SLS, as a key issue. It costs a lot of money and is hard to get off the ground. Last time it flew, in 2022, engineers spent months troubleshooting problems. The issues seem to be repeating this year: NASA wants to launch the SLS to send humans around the Moon, yet it is once again struggling with fluid leaks as the rocket prepares for lift-off.

To solve this, he says, NASA needs to fly the rocket more often. That would give engineers more experience working with it, and would allow for more opportunities to perfect the complexities of launching it. To that end, he wants to launch the rocket four times over the coming three years.

The next launch should come in the next few weeks. That will be Artemis II, a mission that will send astronauts on a loop around the Moon. Nothing has changed there. But Artemis III – which was supposed to support the first lunar landing in five decades – will now only reach Earth orbit. Engineers will use the mission to practice docking the Orion capsule with either SpaceX’s or Blue Origin’s lunar lander, a step that will be needed before crews can head to the surface.

In 2028, Isaacman wants the agency to try for two Moon landings, both of which would put human boots on the regolith. Yet it remains to be seen if America’s space industry can meet the challenge. The SLS has been delayed many times before, and neither SpaceX nor Blue Origin have yet shown they can get a human lander anywhere close to the Moon.

Even so, Isaacman’s approach is probably the best chance America has of landing an astronaut on the Moon this decade. 2028 may still be too ambitious a goal. But his revised plans signal a willingness to consider other options, and to put industry – including SpaceX – on notice.

JUNO Spots 3I/ATLAS

Back in November, the interstellar comet 3I/Atlas reached its closest point to the Sun. Unfortunately for us, the comet then lay on the far side of our star and so was hidden from view of our telescopes.

Luckily, however, Europe’s JUICE spacecraft was positioned for a better view. It is nearly three years into its eight-year-long voyage to Jupiter, and in November it also lay behind the Sun. Operators thus took the opportunity to direct its cameras to study the comet.

But as JUICE was behind the Sun, it was unable to immediately send the data it collected back to Earth. Instead it stored it onboard. When it emerged, earlier this year, it transmitted the photos and measurements it collected back to mission control.

ESA has now released the first of these images. They show the comet as seen from a distance of sixty-six million kilometres, and reveal it to be surrounded by an egg-shaped halo of gas. Behind it streams a faint tail of particles, making it look rather like any other comet approaching the Sun would.

Researchers will now study the rest of the data JUICE sent back. Later in March they will meet to discuss what they have found – and what the observations can tell us about what the comet is made of and where it might have come from.

3I/Atlas itself is now approaching Jupiter. It should make its closest approach to that planet on March 16. Afterwards it will fly onwards and begin to fade from view. But the simple fact it has traversed the distance from Mars to Jupiter in mere months hints at its impressive speed: JUICE will take another five years to cover the same distance.

Life and Asteroid Impacts

Sixty-six million years ago, an asteroid at least six miles wide smashed into a shallow sea close to what would one day become North America. It left a crater eighteen miles deep, and blasted a trillion tons of rock and dust upwards. Much of that fell back to Earth, set everything on fire, and contributed to the extinction of the dinosaurs.

Yet some of that rock escaped our planet. Over the next few million years, pieces of Earth fell on Mars, or burned in the thick atmosphere of Venus. A fraction of it even reached the moons of Jupiter and Saturn, and there it likely plunged into the deep oceans that lie under their icy surfaces.

It is all but certain that some living creatures were blasted into space along with all that debris. Since experiments on the International Space Station have shown that some hardy bacteria can be revived after spending years exposed to the vacuum of space, it seems likely that some lifeforms survived this initial ordeal.

Now, an experiment has found that some of those same bacteria are also capable of surviving intense shocks and pressure waves. That came as a bit of a surprise, the scientists conducting the experiment said. The shocks were expected to rupture the cell walls of these creatures and so kill them. Instead the experiment found that almost all of them survived.

This lends even more weight to theories of panspermia, the idea that life has emigrated between the planets. And since Earth rocks surely lie at the bottom of oceans on Titan, Europa, and Enceladus, it strengthens the idea that we may soon find evidence of thriving colonies of bacteria elsewhere in the solar system.

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America’s billionaires are suddenly obsessed with the idea of building data centres in orbit. Elon Musk has, as usual, taken the lead. In the past month he has merged his AI company with his rocket company, and applied for permission to launch a million satellites into orbit. Within the decade, he says, this company will build a city on the Moon dedicated to pumping out an endless stream of AI spacecraft.

He is not alone. Google is pursuing an AI moonshot, and wants to put prototypes in orbit as soon as possible. Starcloud, a start-up funded by Y-Combinator and backed by NVIDIA, has already put AI chips in orbit, and wants to build a constellation of eighty thousand satellites. Amazon founder Jeff Bezos thinks the first gigawatt-scale data centres will be in orbit by the 2040s.

The question, though, is why anyone thinks this is a serious idea. Working in space is hard. Very few things make economic sense in orbit. Those that do - communications, navigation, and observation – are feasible only because their advantages outweigh the tremendous downsides of launching equipment into the vacuum of space.

Much of the current noise is coming from the rapid build-out of data centres for AI. Training the models behind apps like ChatGPT takes a lot of processing power – we’re taking hundreds of megawatts here, or the demand of a small city – and the difficulty of getting this power supply fast enough is threatening to curtail the race towards ever more intelligent machines.

Building more power stations is the obvious answer, but this takes time and getting the necessary permission to build new plants is a lot of work. For a while it looked like nuclear fusion might be the answer: OpenAI and Google both poured millions into start-ups claiming they could build a working reactor. But progress, as always, has been slower than the hype, and the AI companies have impatient investors to satisfy.

Why not, then, turn to the giant fusion reactor we call the Sun? It has provided us with a steady stream of energy for the past few billion years. The most direct way to access that power is with solar panels, and on paper these can be deployed in such numbers as to provide us and our data centres with all the power we could ever need.

But doing this on the Earth’s surface has some drawbacks. The most obvious is the night – after the Sun sets, solar panels are useless. Yet even when the Sun is shining, its light can be blocked by clouds, and since the Earth wobbles as it spins the intensity of the Sun’s light varies over the course of a year.

So why not put the panels in space? With the right orbit you can ensure they are almost always illuminated. There is no atmosphere to weaken the Sun’s rays, and neither are there any clouds to block them out. Panels can easily be oriented to maximise their exposure, and as a result solar panels can in theory produce much more energy in space than they can on Earth.

Even better, at first glance this energy looks cheap. Solar power is free and almost endless, and once the satellites are in orbit they require little in the way of maintenance. Their numbers can scale almost without limit, with no neighbours to complain or landowners to bargain with.

Into The Great Wide Open

So what’s not to like about endless free energy? Musk in particular seems enamoured with the idea. His constellation, he claims, will propel consciousness into a new age, one in which we convert the entire energy output of the Sun into the musings of an artificial intelligence. Humanity might not survive that – who knows what such a being might think of us – but that does not matter, just as long as the spark of consciousness lives on in this wondrous creation.

Yet there are basic problems with the idea. Much ink has already been spilt on the topic. One is a basic question of thermodynamics: every watt of energy a spacecraft takes in must somehow be later expelled. If you don’t or can’t do that, then it will heat up, and heat quickly becomes a problem for computers. Indeed, most data centres on Earth put a lot of effort into keeping their processors cool.

Fortunately space is cold, enthusiasts say. What they really mean is that the vacuum of space is cold. Astrophysicists have measured its temperature, and found it to be only a few degrees above absolute zero. But the vacuum is also a good insulator, and so heat does not conduct away from spacecraft as it would on Earth. Instead, a spacecraft can only lose heat by radiation, and this is not an efficient process.

Engineers thus put a lot of effort into controlling heat flow in and out of spacecraft. Some deploy enormous heat shields to reflect the light of the Sun away; others are fitted with special devices to radiate heat as efficiently as possible. Inside, they run heat pipes and pump fluids to cool computing devices and to push heat to places where it can be expelled.

Simply capturing enough solar power is another problem. Each megawatt you need demands at least eight hundred square metres of solar panels1. Such enormous arrays quickly become a challenge to manoeuvre and position. Even worse, the good orbits are full of old satellites, pieces of debris, and micrometeorites. Avoiding collisions becomes imperative, and will become a nightmare task even the smartest AI will struggle to solve.

Yet even if you can solve these fundamental questions – and with enough ingenuity and equipment you can probably get close – you still face issues of radiation, of degrading solar panels, of replacing failed processors, and of keeping your whole system up-to-date with the latest AI chips developed back on Earth.

These are all, in truth, engineering problems rather than showstoppers. But they are each a downside to the dream of unlimited free energy. Addressing them costs money, lofting them into orbit costs more, and pretty soon all that free energy starts to look rather expensive after all.

One Day, But Not Today

In 2012, Popular Science ran an article titled “Why Mining an Asteroid for Water and Precious Metals Isn’t as Crazy as it Sounds”. Back then, asteroid mining was all the rage. The usual suspects rushed to invest, hoping to stake a claim to the minerals of the future. Eric Schmidt and Larry Page of Google poured in cash, as did the director James Cameron. Even countries got involved – in 2016, the Grand Duchy of Luxembourg invested millions of dollars into the concept.

Of course, it went nowhere. The over-hyped start-ups were sold off – one smoothly transitioned into blockchain services – and the idea of mining asteroids now lingers as a faintly embarrassing episode in the history of spaceflight. In many ways the concept was doomed by the technology needed. It could one day be done, perhaps, but it would take a solid decade or two of consistently pushing the frontiers of spaceflight.

Nor did the sums really add up. The minerals investors dreamed of are all already available on Earth. If the demand for them were there, we could extract them more easily and cheaply from the bottom of the sea, or from deep in the Earth’s crust. Both would be far simpler than venturing into the depths of space and landing on an asteroid.

Is history repeating itself? Last week, The Economist ran an article entitled “Data Centres in Space: Less Crazy Than You Think”. It lays out a possible path to building orbiting facilities at lower cost than on Earth. But look closely and the argument is flawed2. It relies on technologies that haven’t been developed, on contradictory assumptions, and on unrealistic input costs.

The only real difference this time may be the deep pockets of Elon Musk. He could, if he wishes to, build orbiting data centres at a loss. With enough money, many of the engineering obstacles might be overcome. Prototypes could be launched. But it still won’t be cheaper than doing it back here on Earth. The sums simply don’t add up.

One day, decades from now, things might look different. Asteroid mining would be viable if we had a use for the minerals in orbit. The hard part is often the transfer between Earth and space – if you never bring the rocks back to the surface, then perhaps a profit is to be had. The same might be true for computing power in orbit. For certain applications, it may one day become cheaper to keep everything in space.

Yet until that day comes, the idea really is crazy. And if you have to keep reassuring people it isn’t, you are probably wrong.

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