Imagine a galaxy teeming with planets, many of which could harbor vast oceans of water, not because they formed in the icy outskirts of their solar systems, but due to a surprising chemical reaction deep within their cores. This groundbreaking discovery challenges everything we thought we knew about how water forms on distant worlds.
A team of Israeli and American scientists, led by Prof. Dan Shim of Arizona State University and Prof. Alona Vazan of the Open University of Israel, has uncovered a fascinating process that could explain the presence of water on countless planets. Published in Nature (https://www.nature.com/articles/s41586-025-09630-7), their study reveals that under the extreme conditions inside sub-Neptune planets—worlds two to four times the size of Earth—dense hydrogen can react with molten rock to produce significant amounts of water. But here’s where it gets controversial: this process could mean that many planets don’t need to form far from their stars to be water-rich, as previously believed.
Sub-Neptunes, with their rocky and metallic cores enveloped in thick hydrogen-rich atmospheres, were once thought to require migration from colder regions to acquire water. However, the new research shows that hydrogen-magma reactions alone can generate water in quantities far exceeding earlier predictions—up to tens of weight percent. Using advanced techniques like diamond anvil cells and pulsed laser heating, the team replicated the intense pressures (several gigapascals) and temperatures (around 3,000 Kelvin) found at the boundary between a sub-Neptune’s core and its atmosphere. Here, hydrogen reduces silicon and iron in molten rock, releasing oxygen that bonds with hydrogen to form water. The experiments detected both water and silicon-hydrogen compounds, confirming the reaction’s efficiency.
And this is the part most people miss: earlier models, based on low-pressure assumptions, predicted only trace amounts of water from such reactions. The new findings show water production 2,000 to 3,000 times higher! Computer simulations further reveal that convection can distribute this water throughout the planet’s interior, sustaining production for billions of years as long as molten rock remains. This process could naturally transform hydrogen-rich sub-Neptunes into water-rich worlds, blurring the lines between planet categories once thought distinct.
The implications are profound. If sub-Neptunes can generate water internally, it reduces the need for large-scale migration to explain water-rich planets orbiting close to their stars. Even planets formed from dry materials could eventually contain substantial water. Over time, if these planets lose their hydrogen atmospheres due to stellar radiation, they might shrink into super-Earths while retaining significant internal water. This water could later emerge on the surface or in the atmosphere as the planet cools.
Prof. Shim notes that these findings reshape our understanding of which planets might support water. Prof. Vazan adds that the study challenges the long-held belief linking a planet’s water content to its orbital position. The takeaway? Detecting water in an exoplanet’s atmosphere doesn’t necessarily mean it formed far from its star. But here’s the thought-provoking question: If water can form internally on so many planets, does this increase the likelihood of extraterrestrial life? Share your thoughts in the comments—let’s spark a discussion!