Research provides new insights into water distribution in rocky exoplanets

New research suggests that rocky exoplanets, particularly those that have hosted or still host magma oceans, may hold significant amounts of water deep in their cores. Up to 95 percent of a planet’s water may be stored in its molten iron core, rather than existing as surface oceans. This discovery changes our understanding of water-rich worlds and their potential habitability, indicating that these planets may have more abundant water than previously thought, but that most of it is inaccessible.

When planets form, they undergo intense heating, which leads to the creation of magma oceans. During this phase, water dissolved in the magma can migrate to the planet’s core. To research show that Earth-like planets can pull this water down, but on larger super-Earths this process may be even stronger. Computer models have revealed that on these larger planets much of the water gets trapped in the core, absorbed by iron rather than staying close to the surface.

While water is essential for life, it is locked so deep within the planet that it is inaccessible, posing challenges to the potential habitability of the surface. However, the presence of water in the core can still play a role in the overall habitability of a planet, potentially affecting the planet’s magnetic field or geological activity. Detecting water in an exoplanet’s atmosphere could indicate that much more water is hidden in its interior, changing our search for habitable worlds.

An intriguing example is the exoplanet TOI-270d, which is located 73 light-years away. Recent observations have detected water vapor in its atmosphere, suggesting that there may be a lot of water trapped in its core. This finding underscores the need for further exploration of such planets, as the way water interacts inside them could change our understanding of planetary habitability and the distribution of water in the Milky Way.