How Some Alien Worlds Might Make Their Own Water

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How Some Alien Worlds Might Make Their Own Water
Cassidy Ward
Fri, November 14, 2025 at 11:55 AM EST
4 min read



How Some Alien Worlds Might Make Their Own Water


Have you ever wondered how to make water from scratch? Exoplanets orbing other stars may have cooked up a new recipe.

Manufacturing water is a relatively simple chemical process, albeit a dangerous one. All you have to do is mix a little hydrogen gas, a little oxygen gas, and an energy source to activate the reaction. And cross your fingers that you don’t explode.

Energy breaks the covalent bonds between H2 and O2 molecules, allowing them to interact with one another. They recombine to make liquid water, releasing significant energy in the process. That energy can facilitate additional reactions and keep the water engine churning, but that energy is also dangerous. Just ask The Martian’s Mark Watney (Matt Damon).

Far from Earth, a certain group of exoplanets have found another method of creating their own water using hydrogen, rocks, pressure, and heat, according to a recent study published in the journal Nature.


How sub-Neptune exoplanets make their own water from scratch


Planet Comparison


Astronomers have discovered more than 6,000 exoplanets, some of which are surprisingly water-rich, despite existing in places where liquid water was believed to be impossible.

The new study focused on sub-Neptunes, planets with sizes between two and four times the diameter of Earth. Current models of sub-Neptunes assume they have rocky or metal cores, with thick atmospheres of either hydrogen or water. Astronomers expect to find water-rich planets far from their parent stars, out beyond what’s called the “snow line” where temperatures are low enough for water to freeze.

This model of planet formation explains our own solar system pretty well. The inner planets are mostly rocky and dry. Only Earth has a significant amount of surface water and in the grand scheme of things we don’t have that much. Jupiter’s moon Europa, for instance, is only 1,900 miles in diameter (compared to Earth’s 7,926-mile diameter) but it contains two to three times as much liquid water in a global subsurface ocean. It’s not alone, Saturn’s moon Europa also has a global sub-surface ocean. Most of the water in our solar system, both frozen and liquid, exists out past the asteroid belt, beyond the snow line.

Despite this model of planet formation, astronomers have uncovered several sub-Neptunes orbiting close to their stars, where stellar heat should burn away any surface water. Yet, the water remains. The new study offers a novel explanation as to the water’s origin.



Sub Neptune


While heat might be wicking water away, surface water could remain if the planet is actively producing it. Researchers used diamond-cell anvils and lasers to simulate the extreme heat and pressure found on these exoplanets, at the boundary between their thick hydrogen atmosphere and the rocky core. Samples of olivine, fayalite, and silica were exposed to pressures 10,000 times higher than Earth’s atmosphere and temperatures above 3,000 Kelvin (5,000 Fahrenheit).

Inside this miniature crucible, the minerals melted into magma and that’s when the magic happened. As the minerals melted, oxygen atoms were released and able to interact with hydrogen in the atmosphere to produce water. Moreover, silicon forms alloys with iron, making silicon hydrides, facilitating even more water-producing reactions.

According to this new model, these sorts of reactions could be enough to transform hydrogen-rich worlds into water-rich worlds over the course of billions of years. If so, these hydrogen-rich sub-Neptunes could be water worlds in waiting, metamorphosing into more habitable worlds after passing through their chemical cocoon.

The findings reframe our understanding of where water could exist in the universe and what sorts of planets might be habitable. It could mean that watery worlds are more common that we previously supposed and that habitable worlds might be easier to find.

https://www.yahoo.com/news/articles/alien-worlds-might-own-water-165500102.html