The Week in Space and Physics: The First Molecules of Water
On the origins of water, a survey of the Radcliffe Wave, Moon landings, and the eighth flight of Starship.
When did water first appear in the cosmos? Today, of course, there is a lot of it around. The Earth is only one example of that, since astronomers have found water worlds across the galaxy and spotted signs of the stuff in faraway galaxies. And some of it seems to be remarkably old. In one recent case, for example, a telescope picked up the signature of water molecules in a galaxy seen as it was just seven hundred million years after the Big Bang.
Early on, however, the story must have been different. No water was created directly by the Big Bang, and the first atoms, when they came together, were mostly simple ones like hydrogen or helium. No water was possible then, either, since for water to form hydrogen must bond to oxygen, and in the beginning oxygen was vanishingly rare.
So it was only with the arrival of the first stars, a new study argues, that water could have formed in any reasonable quantity. These were not stars as we know them today, but instead vast beasts fed by a supply of almost pure hydrogen. Some may have grown to incredible sizes, astronomers reckon, before imploding into enormous black holes. Those that survived burned bright and they burned fast, and when they died they must have unleashed cataclysmic supernovae.
We have yet to see the light from any of these stars. Even the James Webb lacks the power to spot them, although some tentative signs of their existence have been found. But researchers are confident they must have existed, even if we are not yet sure how big they were or what happened to them when they died.
We do know, however, that supernovae are able to produce heavy elements. And early on, when those first stars began to die, their supernovae probably produced atoms of oxygen. In the new study, led by researchers at the University of Portsmouth in Britain, researchers looked at models of how those supernovae may have played out.
They found that oxygen atoms surely were produced. And, indeed, that some of them may have combined with hydrogen atoms to create water soon after a dying star exploded. Yet in the early phases of a supernova, this mingling of atoms would have been limited to the clouds of debris being flung out. In general, their models showed, these were too sparse to produce much in the way of water.
Later on, though, much more water could have formed in the cooling core of the supernova. Their calculations suggest the death of a big star, one two hundred times more massive than the Sun, would have created a volume of water enough to fill the oceans of Earth thousands of times over. Most of that would have formed and lingered around the supernova’s core. And some of it might, they speculate, have ended up on the first rocky planets.
If so, we might be able to find one. There are ancient stars in our galaxy, some of which probably formed from the remains of that first brilliant generation. If we find planets around them, and if we find signs of water on them, we might find ourselves looking at some of the very first molecules of the stuff ever created.
The Solar System’s Dusty Past
Fifteen million years ago the solar system may have passed through a cloud of dust and gas. If it did, traces of that cloud might still be present deep under the ocean floor, buried in layers of sediment and mingled with the bones of long dead creatures.
That, at least, is the conclusion from a recent study of the Radcliffe Wave, a region of gas and dust that snakes it way through our interstellar neighbourhood. This wave is not easy to see. Indeed astronomers only discovered it in 2020, thanks to the detailed observations made by the Gaia space telescope.
Even so, the Radcliffe Wave does seem to be large. Measurements suggest it spans thousands of light years, and that it contains several clusters where new stars are forming. For reasons still unknown, the wave moves as a single structure, undulating as it rotates with the spiral arms of the galaxy.
Our star is not part of the Radcliffe Wave, nor was it born there. Yet it may well have passed through the wave in the recent past. According to simulations carried out by Efrem Maconi, the Sun should have been within the dust and gas clouds about fifteen million years ago.
If so, that would have had some impact on our planet. Maconi speculates that dust from the cloud would have obscured the view of the stars from Earth. It might also have blocked some of the light and heat coming from the Sun, triggering a period of cooler weather. Indeed, our passage through the Radcliffe Wave seems to coincide with the Middle Miocene Cooling, a period when the Earth’s temperature fell and the ice sheets expanded.
Yet the climatic effects of the wave are speculative. The cooling would have been slight, and other factors, such the movements of tectonic plates and the disturbing effects of volcanoes on the atmosphere, are probably more influential.
Still, traces of the cloud could linger. Dust from it would have fallen on the Earth’s atmosphere, and eventually found its way to the bottom of the oceans. A faint layer of interstellar dust might one day be found there, and so reveal the history of our Sun’s voyage through the galaxy.
A Tale of Two Moon Landings
It was the best of landings; it was the worst of landings.
Last week two American probes made it to the surface of the Moon. For one it was a triumph; the first fully successful American landing on the Moon in decades and the first private company to pull off the achievement. For the other it was a disaster, and the probe, after spending a few hours on the surface, was declared dead.
The triumph belonged to Firefly, a rocket company that had never before attempted to land anything on the lunar surface. Their lander, named Blue Ghost, launched in January. After taking about six weeks to approach the Moon they manoeuvred for landing on March 2, and then touched down in the Mare Crisium, a region neighbouring the Mare Tranquillitatis (“Sea of Tranquillity”) visited by Neil Armstrong and Buzz Aldrin.
A different fate, however, awaited the probe from Intuitive Machines, a company that already attempted to land on the Moon last year. In that flight, known as IM-1, the lander broke a leg as it touched down and fell over onto its side. Exactly what went wrong this time is still unclear, but the probe, IM-2, seems to have once again tipped over. A few days after the failed touchdown, the company acknowledged the probe had failed.
Firefly’s Blue Ghost will now spend the next two weeks in daylight, during which it will conduct experiments for NASA. After that it will experience a long and cold lunar night, during which its batteries will run down and the probe will turn off. Survival until the next dawn is not impossible – a handful of past probes have done it – but Firefly does not expect Blue Ghost to make it more than a few hours into the harsh lunar night.
Starship Fails... Again
On Thursday SpaceX’s Starship exploded as it climbed into space, sending debris raining across a wide area of the Caribbean Sea. The failure was the second in a row for Starship, and comes after a test flight in January blew up during a similar phase of the mission.
SpaceX seems certain to push on with Starship development. And, to be fair, they have made good progress with the actual “rocket” part of the spacecraft, the so-called Super Heavy Booster. On Thursday they managed once again to catch it after it separated from Starship, a step that is crucial to eventually reusing the booster.
Yet the Starship part – the bit that actually goes into space and that NASA hopes will someday take astronauts to the lunar surface – is clearly in trouble. SpaceX were already struggling with attitude control and the hard challenge of re-entry and landing. The latest setbacks show that even reaching space can be hard enough.
I’d never considered how old water was until I stood by the Lindsay creek, Puke-haukea, in Dunedin trying to write a poem about it. As I tuned in I wondered - how old is this water? As old as the sunrise? And now you’ve made me think - maybe even older. It’s interesting to think of our engagement with water as participating in, and linking to the past.