Laboratory experiments published in Nature show that water can form during planet formation when hydrogen-rich atmospheres interact with molten, iron-rich rock. Using a diamond anvil cell at nearly 600,000× Earth’s atmospheric pressure and temperatures above 7,200°F (4,000°C), researchers observed hydrogen reacting with iron oxides to produce water. The result implies water may be a common byproduct of planetary assembly, increasing the prospects for habitable worlds — though the mechanism is most relevant to planets with thick hydrogen envelopes.
Planets Can Make Their Own Water as They Form — Boosting the Chances for Habitable Worlds
Laboratory experiments published in Nature show that water can form during planet formation when hydrogen-rich atmospheres interact with molten, iron-rich rock. Using a diamond anvil cell at nearly 600,000× Earth’s atmospheric pressure and temperatures above 7,200°F (4,000°C), researchers observed hydrogen reacting with iron oxides to produce water. The result implies water may be a common byproduct of planetary assembly, increasing the prospects for habitable worlds — though the mechanism is most relevant to planets with thick hydrogen envelopes.
10:09 AM, 11/11/2025Science
Planets Can Make Their Own Water as They Form
New laboratory experiments show that liquid water can form naturally during the early stages of planet formation when hydrogen-rich atmospheres interact with molten, iron-rich rock. The study, published Oct. 30 in Nature, reproduces extreme conditions found inside young, growing planets and demonstrates a direct chemical pathway from rock and gas to water.
How the experiment worked
Researchers led by Anat Shahar of the Carnegie Institution for Science recreated a miniature version of a sub-Neptune — a common class of exoplanet larger than Earth but smaller than Neptune — using a diamond anvil cell. They compressed molten, iron-rich rock between two diamond tips to nearly 600,000 times Earth’s atmospheric pressure and heated it above 7,200°F (4,000°C), approximating the conditions deep inside a molten planet.
What they found
Under those furnace-like conditions, hydrogen from the surrounding gas dissolved into the magma and reacted with iron oxides in the molten rock to form substantial amounts of water. In other words, water emerged as a natural byproduct of rock-and-gas chemistry rather than requiring delivery by comets or asteroids.
"This work demonstrates that large quantities of water are created as a natural consequence of planet formation," said Anat Shahar, co-leader of the study.
Why it matters
More than 6,000 exoplanets have been discovered in the Milky Way so far, and sub-Neptunes are the most abundant class. If water commonly forms during early planetary evolution when hydrogen-rich atmospheres are present, the number of worlds capable of hosting water — and potentially life — could be far larger than previously thought.
Caveats and next steps
While the results are compelling, they apply most directly to planets that retain thick hydrogen envelopes during their molten phase — conditions that may differ from Earth's formation history. Whether the same mechanism produced Earth's oceans remains an open question. Future studies will test how much of this lab-produced water can be retained, sequestered, or later released to form surface oceans, and how the process scales across different planet sizes and compositions.
Bottom line
The experiments provide a realistic demonstration that water can be forged during planet formation through straightforward chemistry between hydrogen and iron-rich magma. This finding broadens our understanding of where water — and potentially habitable environments — might arise in the galaxy.