A new study conducted by researchers from the Swiss Federal Institute of Technology in Zurich (ETH Zurich) and Princeton University completely changes our understanding of water distribution on exoplanets.
Until now, it was believed that water on these planets was primarily located on their surface, as is the case on Earth. However, recent computer simulations show that the majority of water could be buried deep inside, thereby altering our perception of the habitability of these distant worlds.
The researchers focused on the formation and distribution of water on exoplanets, particularly on how it is transported and trapped within their internal layers. Contrary to popular belief, water would not remain mostly on the surface. Indeed, in young exoplanets, water dissolves in the oceans of molten magma that make up their mantle. This magma contains droplets of iron, which, as they sink toward the core, carry with them a significant amount of water, trapping it in the metallic core. This complex internal dynamic challenges previous models that assumed a simple surface water distribution.
These findings have significant implications for assessing the habitability of exoplanets, particularly super-Earths. These planets, far more massive than Earth, have long been considered potentially hostile to life due to their supposed water abundance. It was thought that excess water on their surface could form a high-pressure ice layer, preventing any exchange of vital substances with the underlying rocky mantle. However, the new study suggests that water could be largely trapped deep within, hence reducing these risks and leaving open the possibility of habitable surface conditions.
Current methods for measuring the characteristics of exoplanets, such as mass and radius, rely on models that do not account for this new internal water distribution. Consequently, these models could underestimate the total amount of water present on exoplanets, sometimes by up to tenfold. These results highlight the need to revise the observational and interpretative techniques used to understand the composition of these worlds.
These discoveries also open up new perspectives for the search for life beyond the Solar System. Astronomers, by revisiting habitability criteria, can now target exoplanets where water is abundant not only on the surface but also deep inside. This could expand the list of potentially habitable worlds and guide future space exploration missions towards promising new targets.
This study invites us to rethink our understanding of exoplanets and their potential to harbor life. Water, an essential element for life as we know it, appears to be far more prevalent than expected in the depths of these distant worlds. These results could transform our approach to astrobiology and guide the next steps in space exploration.
Article author: Cédric DEPOND