We assumed water had to be delivered to planets by comets or asteroids — but a 2025 Nature study found that sub-Neptunes, the most common type of planet in the galaxy, can forge their own oceans by reacting hydrogen atmospheres with molten rock deep inside their cores

We assumed water had to be delivered to planets by comets or asteroids — but a 2025 Nature study found that sub-Neptunes, the most common type of planet in the galaxy, can forge their own oceans by reacting hydrogen atmospheres with molten rock deep inside their cores

For a long time the story of how a planet gets its water had one main plot. Water forms easily in the cold outer reaches of a young star system, freezes into the ice that coats comets and distant asteroids, and is then delivered inward when some of those bodies crash into a rocky planet closer to the star. On that account, a world with water was a world that got lucky with its deliveries. A 2025 study in the journal Nature offers a different rou…