The Week in Space and Physics: India and the Moon
On this summer's Moon missions, stars of dark matter, the Mars Sample Return mission and the origins of water.
Everybody, it seems, wants to go to the Moon these days. America and China are leading the way, with the two superpowers vying to once more put astronauts on the lunar surface. Others, from India to Japan, are sending orbiters and landers; each seeking to stake out their part in an emerging race to the Moon.
This summer will see at least three robotic missions head towards our natural satellite. First up was India, who launched the Chandrayaan-3 mission on July 14. After two weeks in space, Chandrayaan-3 is now nearing the point at which it enters lunar orbit. If all goes to plan, the spacecraft will put a rover on the Moon’s surface by the end of the month.
This, of course, is not India’s first attempt at reaching the Moon. Back in 2008 Chandrayaan-1 orbited the Moon, making significant contributions to the discovery of water on its surface while it was there. Chandrayaan-2, however, went less well. Though it reached lunar orbit successfully, a subsequent effort to put a rover on the surface ended in disaster when the lander crashed at high speed.
India, then, will be hoping for better luck this time around. If all goes well, the lander will deploy a rover to carry out geological studies of the Moon’s surface. As they did with Chandrayaan-2, India is targeting a landing near the lunar south pole, a region that has been little explored but is of great interest to planetary scientists.
Both America and China are eying the lunar south pole as they plan human expeditions to the Moon. Key to that interest is the possible presence of water ice hidden in regions permanently shadowed by high cliffs around craters. Controlling, or at least having access, to that ice could be vital for future lunar bases.
Next up after India is Russia. After decades of development, their Luna-25 probe is finally scheduled for launch on August 10th. Like Chandrayaan-3, Luna-25 has both an orbiter and a lander, and is targeting a landing site near the lunar south pole. For Russia’s ailing space program this could be a crucial mission: success will show they are serious about working with China on a future moon base.
The final mission of the summer will probably be Japanese. Should all go well, their SLIM Sniper mission will lift off at the end of August, sharing a ride with XRISM, a new X-ray telescope. Once it reaches the Moon, SLIM will use advanced cameras and algorithms to pick out a landing site amidst rough lunar terrain.
SLIM, its builders hope, will steer itself to a gentle touchdown less than one hundred metres from its chosen target. This, Japan’s space agency says, will allow future missions to land in more difficult terrain - meaning missions can be designed to visit the places we want to, rather than the places that are easiest to land in.
That said, even the kindest parts of the Moon have proved hard to land on. Recent years have seen several probes fail to touchdown on its surface, and neither India nor Japan have ever done so successfully before. Even Russia has not done so for almost half a century - when Luna 24 flew, the country was still part of the Soviet Union.
Yet whether this summer’s missions succeed or fail, they highlight the world’s growing interest in our natural satellite. Over the next decade an abundance of Moon missions are planned, both by governments and private companies. Everyone really does want to go to the Moon these days.
Does Dark Matter Burn?
Dark matter is slippery stuff. We know almost nothing about it, save that it appears to exert a gravitational pull on the more familiar kind of matter that lights up the cosmos. Beyond that it is utterly mysterious; refusing, so far at least, to reveal itself in any experiment ever run.
That, however, doesn’t stop physicists speculating. Back in 2008, a group of American researchers developed models of stars forming in the presence of dark matter. Normally stars ignite when clouds of hydrogen and helium collapse, triggering nuclear fusion reactions. Yet if dark matter is added to the mix, the researchers speculated, that behaviour might change.
When clouds of hydrogen, helium and dark matter collapse, they reckon, the dark matter prevents nuclear fusion from starting. Instead dark matter particles begin annihilating one another. As they do, they create bursts of energy with enough power to create something akin to a star.
Such objects would look rather strange. Calculations suggest they could reach enormous sizes and shine incredibly brightly - with a single one of these stars emitting as much light as a single galaxy of normal stars. They’d also be old, as the dark matter density needed to sustain them would only be found in the early universe.
When the idea was proposed, telescopes were not yet powerful enough to spot any of these ancient stars. Yet the James Webb is, at least if they really exist, and astronomers are now debating whether they have found any. In a follow-up study, the researchers who originally proposed the idea of “dark stars” have now picked out three objects found by the James Webb that they think are worthy of extra study.
Each of these objects looks rather like an early galaxy. But dark stars, the researchers point out, would also look like that. Only with more observations could we distinguish the two, either confirming them as galaxies or unveiling them as vast, bright stars.
If they do indeed turn out to be dark stars, the implications would be enormous. On one side they could reveal the origins of supermassive black holes, since such vast stars would probably have ended their lives by forming such gigantic objects. But, more importantly, they would give us a rare insight into the world of dark matter, proving that particles of dark matter exist and can annihilate one another. That truly would be groundbreaking.
Mars Sample Return in Doubt
Since arriving on Mars two years ago, NASA’s Perseverance rover has been collecting samples of rock and air. More than twenty such samples have been made, each stored in a small tube and carefully stashed away.
NASA hopes to one day bring these tubes back to Earth, giving researchers direct access to pristine Martian samples for the first time. Yet doing so is complex: plans call for a series of missions to retrieve the samples, blast them into orbit and then send them hurtling back to Earth.
Last year NASA reached an agreement with ESA, the European Space Agency, to work together on the mission. Under this plan, NASA will take care of retrieving and orbiting the samples, while ESA will be responsible for ferrying them from Mars to Earth.
This project, planetary scientists said in 2022, should be NASA’s top priority for robotic exploration. Yet at the same time they warned the agency to be careful of costs - should the project grow too expensive, it could swallow up the budget currently allocated to other robotic missions.
That scenario, unfortunately, may be coming to pass. In a recent report, a Senate committee recommended spending just $300 million on the project next year, far less than the $1 billion originally requested. Further, the committee called for NASA to prepare a funding plan that keeps the project within budget.
If they cannot, then the Mars Sample Return will need to be radically rethought or even cancelled outright. Perseverance’s samples, sadly, may end up waiting on Mars for a lot longer than hoped.
Water Spotted Around a Distant Star
Where did all of Earth’s water come from? Astronomers think that much of it came from a rain of asteroids and comets that lasted for millions of years. Yet whether those asteroids and comets originated in the frozen fringes of the solar system or came from somewhere closer by is still unknown.
Now, however, the James Webb telescope has spotted water in a young star system a few hundred light years from Earth. The water appears to be in the inner disc of the system, in a region where small planets, similar to Earth or Mars, may be forming.
That suggests that planets like Earth form with water, instead of accumulating it later. Still, the full implications of the finding are still not clear. Water molecules should, at least in theory, be split apart by the harsh radiation of the young star. How it is surviving - or how it is being replenished - will be the subject of future surveys of the star and its system.