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Lab Experiments Show Sub‑Neptunes Can Make Their Own Water

High‑pressure tests produced water at the hydrogen–magma boundary to challenge migration-based explanations for wet close‑in worlds.

Overview

  • Researchers used a laser‑heated diamond‑anvil cell to recreate the extreme conditions at the interface between hydrogen atmospheres and molten silicate interiors.
  • The experiments showed molten silicates react with hydrogen, liberating oxygen that combines with hydrogen to form water reaching up to a few tens of weight percent.
  • Calculations based on the results indicate these reactions could continue for billions of years, enabling long‑term water production within some sub‑Neptunes.
  • The amount of water produced depends strongly on planetary makeup, with variations in factors such as the Mg:Si ratio significantly altering yields.
  • The findings suggest atmospheric water detections on close‑in sub‑Neptunes are not definitive evidence of formation beyond the snow line or later delivery by icy bodies.