How Hydrogen and Magma Create Water Deep Inside Planets ⚡ экспресс
Sub-Neptunes are a common class of exoplanets that, based on radius-mass ratios, split into hydrogen-rich (dry) and water-rich (wet) types. The thinking was that wet sub-Neptunes form far from the star and migrate inward. High-pressure experiments now reveal that warm, dense hydrogen reacts with silicate melt: silicon gets locked into alloys and hydrides while oxygen hooks up with hydrogen, yielding up to tens of weight percent water—far more than ideal-gas extrapolations at low pressures suggest. Such reactions can produce a continuous spectrum of water content all the way to water-enriched compositions, hinting at an evolutionary link between the two planet types. Hence, a high water fraction in an exoplanet atmosphere is no reliable sign of migration, casting doubt on the traditional tie between composition and formation site.
Sub-Neptunes — worlds slightly smaller than Neptune — are common among exoplanets. They are detected using the transit method (by the dimming of a star), pioneered by William Borucki. Previously, it was thought that such planets were either dry and surrounded by hydrogen, or wet, with large amounts of water. The wet ones supposedly formed far out, where ice gathers, and then migrated closer to their stars. A new experiment breaks this mold.
In the lab, a mixture of hydrogen and silicate melt (magma) was compressed at thousands of degrees. The planet’s depths acted like an alchemical furnace: hydrogen aggressively ripped oxygen from minerals, and from the scorching rock, water was born. This reaction runs to completion: silicon goes into a metallic alloy, and every kilogram of magma yields up to a hundred grams of water — nearly half a cup. The mass fraction of water reached tens of percent, far higher than old estimates based on ideal gas models.
This means a planet with a hydrogen atmosphere and a magma ocean can transform into a water world without leaving its orbit. Atmospheric analysis using spectroscopy (breaking down light) is now unreliable for determining a planet’s place of birth. Detecting water doesn’t prove migration — the planet could have flooded itself. Astronomers studying exoplanets will have to rewrite their biographies.
🎯 One kilogram of silicate magma, after reacting with hydrogen, can yield up to 100 grams of water — that’s nearly half a cup of liquid born right in the planet’s interior.