As increasingly more exoplanets are found all through the galaxy, scientists discover some that defy rationalization—not less than for awhile. A brand new examine, published in Nature, describes a course of that may clarify why a big portion of exoplanets have water on their floor, even when it would not make sense.
Water the place it should not be
A specific class of exoplanets which are between the scale of Earth and Neptune, known as “sub-Neptunes,” typically have a rocky core, which is surrounded by an envelope of both hydrogen or water. This is sensible if the planet varieties farther away from its host planet, in a area the place water can precipitate as ice. Nevertheless, a few of these planets are discovered a lot nearer to their host stars, the place it needs to be too sizzling to carry water on the floor.
Whereas some planets could accumulate a certain quantity of water from incoming comets and asteroids, that does not work for these planets both. The quantity of water that’s usually discovered on their surfaces is simply too excessive for such explanations. Previous experiments have additionally proven that hydrogen can cut back iron in silicates, producing water. Nevertheless, they got here to the conclusion that solely small quantities of water could be produced on the form of excessive pressures skilled on the floor of a sub-Neptune planet.
Water from an surprising supply
The presiding rationalization for the existence of those planets has been that they fashioned someplace previous the snow-line, the place they had been able to accumulating ice, after which migrated inward. However the brand new examine may need a greater rationalization—the planets make water from their very own rocky cores and hydrogen atmospheres.
The examine authors write, “Right here we report experimental proof of reactions between heat, dense hydrogen fluid and silicate soften that launch silicon from the magma to type alloys and hydrides at excessive pressures. We discovered that oxygen liberated from the silicate soften reacts with hydrogen, producing an considerable quantity of water up to a couple tens of weight %, which is far higher than beforehand predicted primarily based on low-pressure supreme gasoline extrapolation.”
In different phrases, the excessive pressures on the sub-Neptune planets, which could be as much as 10,000 occasions the stress of Earth’s ambiance, trigger the silicate rock to be in a magma type. The oxygen is then free to react with the hydrogen within the ambiance and create water—and apparently, in very excessive quantities. These reactions additionally clarify the existence of each hydrogen-rich and water-rich exteriors, as they seem to exist on a spectrum. Because the hydrogen in a hydrogen-rich planet will get used as much as make water, the planet shifts to a extra water-rich planet.
“The response we report right here means that these planet sorts could also be essentially associated: hydrogen-rich sub-Neptunes might be the precursors of water-rich sub-Neptunes and super-Earths. If an extra, unreacted H2 ambiance could be retained, sub-Neptunes with an H2-rich ambiance overlaying an H2O-rich layer above the core (that’s, hycean worlds) could also be fairly widespread,” the examine authors clarify.
A brand new understanding of exoplanet formation
This new view of water formation on planets has a whole lot of implications for scientists. It challenges the concept that water-rich planets should type removed from their stars, suggesting water worlds might be extra widespread and type in surprising locations. It additionally adjustments the way in which scientists view the potential for all times on different planets by increasing the vary of planets that may have water.
Future experiments would possibly incorporate a wider vary of planetary supplies and circumstances in experiments to seize extra planetary variety and decide if related processes would possibly happen on different kinds of planets. Observational research may also refine how exoplanet atmospheric knowledge are interpreted, particularly concerning water detection.
A Information and Views on the analysis was additionally published in Nature.
Written for you by our writer Krystal Kasal, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this text is the results of cautious human work. We depend on readers such as you to maintain unbiased science journalism alive.
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Extra data:
H. W. Horn et al, Constructing moist planets by way of high-pressure magma–hydrogen reactions, Nature (2025). DOI: 10.1038/s41586-025-09630-7
Quentin Williams, To make water, exoplanets would possibly simply want some stress, Nature (2025). DOI: 10.1038/d41586-025-03214-1
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Scientists discover a proof for oddball, water-rich exoplanets: They make their very own water (2025, October 30)
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