The Week in Space and Physics #2
What lies beyond the edge of the Solar System? For the last ten million years the answer has been almost nothing. The Solar System sits in a vast empty bubble; a void of space swept almost clear. Science has known this for half a century, but quite why and how this bubble came to be has long been mysterious.
That’s not to say the void, known as the Local Bubble, is empty of stars – our Sun is not alone in space – but rather to say it contains much less gas and dust than it should. Most of the galaxy is strewn with clouds of gas – mostly hydrogen – that over long periods of time collapse into stars. Around our Solar System, however, these gas clouds are absent.
To explain why, a team of astronomers in the United States reconstructed the last few million years of galactic history in our neighbourhood. Roughly fourteen million years ago, they think, a series of supernova erupted at the heart of the local bubble. Two star clusters are likely at fault: together they could have produced around fifteen supernovae in the past fifteen million years.
That would have created an expanding shockwave around the clusters, which, over millions of years, swept the region clean of dust and gas. Indeed, evidence suggests that the shell of the Local Bubble – which currently sits around five hundred light years from Earth – contains thick clouds of dust. Those were probably swept up by the supernova shockwaves.
Interestingly, that seem to have triggered a new wave of star birth. The astronomers mapped all known star forming regions around the Solar System. Each, they discovered, lies on the surface of the bubble. Within the Local Bubble, by contrast, they found no star forming regions at all.
This suggests that several supernova exploding a few million years ago can explain almost all of the new stars we see forming around us. That is quite remarkable – and hints that earlier ideas about supernova triggering star birth are correct.
The Earth was almost certainly nowhere near the local bubble when it started to form. Our Sun’s path through the galaxy likely carried us into the bubble a few million years ago, and, by chance, we happen to now sit almost exactly in its centre. That, the researchers note, seems too lucky to be a coincidence.
Instead astronomers think the galaxy must be filled with such bubbles. A handful of others around the Local Bubble are known, but quite how widespread they are remains unknown. Some speculate that the galaxy is riddled with bubbles. Connections between may even form chimneys and tunnels stretching across interstellar space. If so, that could have greatly affected the history of star formation in our galaxy.
Touching the Void
Our Solar System may lie within an enormous void, but it is not quite empty of matter. Indeed, the Sun currently sits inside a small cloud, an area in which gas and dust are slightly more concentrated. Since the dawn of civilization – and likely a great deal longer – the Sun has been moving through this cloud. Within a few thousand years, however, it will reach the edge and plunge back into the void.
Studying the space around our Solar System is hard. Telescopes, of course, can reveal much about the shape and concentration of gas clouds and voids. They can’t, though, give as much detail as a probe might – if only we could get one there.
A handful of probes – notably the Pioneer and Voyager spacecraft – have reached the edge of interstellar space. Unfortunately, since neither was designed for such a mission, they took decades to arrive and return little useful data. Now, however, some are proposing a more ambitious effort: a probe that could travel deep into interstellar space, and send back reams of data just a decade or two after launch.
The concept is named the Interstellar Probe, and was, last month, the subject of a five hundred page report from the John Hopkins Applied Physics Laboratory. In it, the authors propose sending a probe at enormous speeds towards the edge of the solar system. Within a handful of years it would zoom past the orbit of Pluto, through the Kuiper Belt and into the mysterious Oort Cloud.
Then – roughly fifteen years after launch – it would break free of our Sun’s influence and enter interstellar space. From that moment on astronomers would receive a steady stream of valuable date. The authors believe the probe could send back gigabytes of data a year for a least three decades - and might keep working for up to a century.
Such a long mission duration raises new issues for operators back on Earth. A mission fifty, or a hundred, years in length implies generations of engineers and scientists will work on it. Managing that successfully, ensuring that all required knowledge is passed down through the years, will be a challenge as great as building the probe in the first place.
A Devastating Eruption in Tonga
Scientific data on the eruption in Tonga last week is still hard to come by. The priority, of course, is to address the basic needs of the inhabitants of those islands – still struggling with the aftermath of a tsunami and heavy rain of ash. Yet working out precisely what happened is vital to understanding the eruption and to predict what the volcano might do next.
Back in 2016 researchers discovered the volcano has a vast underwater caldera, one that hints at previous big eruptions. A series of small eruptions in 2009 and 2014 might – they think – have been signs that the volcano was filling with magma. They also found traces of ash on nearby islands, which suggested the volcano erupted violently around 1100 AD.
The eruption last week certainly was big. Satellite imagery shows an enormous explosion: one probably caused by a huge surge of magma. Quite how that explosion resulted in a tsunami, however, is not yet clear. Volcanoes rarely cause tsunamis by themselves , and even if the caldera had completely collapsed – as seems possible – that should not have been enough to produce such big waves.
Researchers are now divided about whether this eruption is a precursor to months or even years of activity, or if the volcano will now settle down for another thousand years of sleep. Early signs suggest that the volcano has been fairly calm since the eruption.
Will Artemis I Finally Launch in March?
NASA’s return to the moon – Project Artemis – may kick off at the end of March with the launch of Artemis I. Though the mission has previously been delayed multiple times, NASA appears confident enough in its latest prediction to start inviting journalists and other observers to the launch.
Artemis I, if things go to plan, will be the first launch of the new SLS rocket, a gigantic and incredibly expensive rocket NASA has been working on for over a decade. After reaching space, the SLS will deploy the Orion capsule: a spacecraft designed to ferry astronauts to the Moon.
Though the first flight will be unmanned, NASA are hoping to test the capabilities of the capsule and rocket. Orion will likely spend three weeks in space. At least a week of that should be spent in orbit around the Moon.
Even if all goes to plan, Artemis II will not follow for at least eighteen months. That mission – which should see the first astronauts fly around the Moon in decades – is currently scheduled for May 2024.