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"... It may come as a surprise, then, that scientists don’t really know how water first arrived here on Earth. ...
When astronomers look at exoplanets — worlds outside our solar system — they see a diversity of atmospheres. But when they simulate the ways the planets took shape, scientists find that many of them could have started out brimming with hydrogen. Could Earth’s formative years have been similar? ...
But in recent years, several spacecraft caught up to comets to examine them. What they found was that cometary water didn’t match ours; the chemical signatures were different. ...
Asteroids — rockier and more metal-rich than comets — then became the most popular choice. Asteroids impact Earth far more frequently than comets do, and their water reserves (while not as voluminous as those of comets) look a lot more like those on our planet. ...
Through careful observation of worlds orbiting other stars, along with some explosive laboratory experiments involving diamond anvils and lasers, scientists have realized that rocky planets like Earth have a way to make water all by themselves. All you need is an ocean of magma, a whole lot of hydrogen, and a little bit of geological alchemy. ...
asteroids. These rocky objects mostly hang out between Mars and Jupiter, and they impact our planet all the time as meteorites, though most of their material burns up in the atmosphere or lands in the ocean. Scientists have collected tens of thousands of meteorites and found that the water molecules contained in a particular group closely resemble those in our world. ...
But some studies ... found that there was hydrogen in the meteorites all along. It was just hidden in their organic molecules, silicate glasses, and sulfur compounds. Perhaps, then, Earth was also awash in hydrogen in its early days.
Earth’s ocean of magma was full of oxygen. In a paper published in 2023, three scientists wondered what might happen if the hydrogen in a planet’s atmosphere and the oxygen in its magma were to mix — somehow. Hydrogen doesn’t just spontaneously bind to oxygen, so they aren’t the most willing chemical partners. Still, the researchers concluded that such a process would let a planet make its own water; they just weren’t sure how much.
Two years later, they were thrown a lifeline by an ambitious set of experiments built by the researchers ...
how sub-Neptunes, commonplace exoplanets two to four times the diameter of Earth, can have atmospheres rich in water, as telescopic observations suggest, even when they hew close to their scorching-hot host stars. ...
if a huge amount of hydrogen put the magma under a sufficient amount of pressure. “That higher pressure is a big part of what facilitates the water production,” ... “It actually enhances the chemical reactions.” ...
To test their model, the team wanted to re-create the extreme (and extremely dangerous) conditions present on adolescent sub-Neptunes. They needed to put hydrogen, a highly flammable gas, under intense pressure using special tools called diamond anvils, and then combine it with rock samples melted with lasers. It took them five years to develop the techniques they needed to conduct these experiments safely and effectively. ...
They had hoped the hydrogen and oxygen would react to make water. And that’s what happened, to the extreme: The reaction of high-pressure hydrogen and laser-melted rock was so efficient that it made up to 1,000 times more water than scientists predicted. (A second laboratory study, published around the same time, reported similar results.) “It doesn’t seem unreasonable [that you could] produce a huge amount of water quite quickly,” ..."
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