More than 6,000 exoplanets have been identified in the Milky Way, with Sub-Neptunes the most common. These worlds are less massive than Neptune, larger than Earth, and feature rocky interiors below thick hydrogen-dominated atmospheres. The nature of these planets makes them ideal candidates for investigations into how rocky planets, including Earth, acquired significant quantities of water - considered vital for the emergence of life and planetary habitability.
"Our rapidly increasing knowledge about the vast diversity of exoplanets has enabled us to envision new details about the earliest stages of rocky planet formation and evolution," Miozzi said. "This opened the door to considering a new source for planetary water supplies - a long-debated mystery among Earth and planetary scientists - but experiments designed with this purpose in mind were absent."
The research is part of the AEThER project, led by Shahar and funded by the Alfred P. Sloan Foundation, combining experts in astronomy, cosmochemistry, planetary dynamics, petrology, and mineral physics. The initiative probes how rocky planets develop conditions favorable for life, linking atmospheric observations to the evolution of their interior bodies.
Earlier modeling demonstrated that atmospheric hydrogen and iron-bearing magma oceans could theoretically yield sizeable water quantities during planet formation. Comprehensive experiments testing this process were performed for the first time by Miozzi and Shahar's team. They simulated the young planetary environment by compressing samples to nearly 600,000 times atmospheric pressure and heating them above 4,000 degrees Celsius.
This experimental setting replicates a critical phase in rocky planet evolution, as disk material surrounding newborn stars accretes, collides, heats, and ultimately forms a vast magma ocean enveloped by hydrogen. Molecular hydrogen can act as a "thermal blanket," sustaining the magma ocean for billions of years before cooling.
"Our work provided the first experimental evidence of two critical processes from early planetary evolution," Miozzi explained. "We showed that a copious amount of hydrogen is dissolved into the melt and significant quantities of water are created by iron-oxide reduction by molecular hydrogen."
Findings confirm that large amounts of hydrogen can be stored in the magma ocean as water forms. This discovery has major implications for the physical and chemical properties of planetary interiors, core development, and atmospheric composition.
"The presence of liquid water is considered critical for planetary habitability," Shahar stated. "This work demonstrates that large quantities of water are created as a natural consequence of planet formation. It represents a major step forward in how we think about the search for distant worlds capable of hosting life."
Research Report:Experiments reveal extreme water generation during planet formation
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