2024-08-21 22:48:02
The arid and sterile appearance of some rocky exoplanets does not necessarily imply that they lack water. As much as 95% of the resource could be found in the depths of the mantle and core, although not exactly as one might expect. A recent study from the Swiss Federal Institute of Technology Zurich (ETH Zurich) challenges the traditional model of water distribution on other worlds.
Recent glimpses of satellites and dwarf planets have shown that water definitely exists elsewhere and is likely not a scarce resource. Astronomy no longer questions whether water exists on worlds beyond Earth, but rather its form, proportion, and location.
For a long time, it was believed that water on other planets would be distributed like on Earth: on the surface. However, recent evidence demonstrates that water on a planet or moon may instead be found in the form of underground oceans or even in more unexpected places. For example, on the Moon, there are indications of water contained in crystals and hydrated minerals.
Water yes, but in a iron capsule
A new hypothesis suggests that water on Earth-like exoplanets is mixed with the core’s iron since its formation, in the form of gas. Only through small seepages in the internal structure would the water move toward underground seas in the mantle and eventually emerge as oceans on the surface. Three astrophysicists from ETH Zurich have modeled this possibility in a report titled “The Interior as a Dominant Water Reservoir in Super-Earths and Sub-Neptunes” in Nature Astronomy.
“The larger the planet and the greater its mass, the more water tends to associate with iron droplets and integrate into the core. Under certain circumstances, iron can absorb up to 70 times more water than silicates. However, due to the enormous pressure in the core, water is no longer found in the form of H2O molecules but is broken down into hydrogen and oxygen,” explains Caroline Dorn, co-author of the study and professor of exoplanet science at ETH Zurich.
For the research, scientists drew inspiration from works on the proportion of water on Earth, suggesting that surface oceans contain only a fraction of the planet’s total water. The resource in other forms should be inside, still inaccessible. Earth’s mantle represents 84% of its total volume, extending from 33 km to 2,900 km deep. In comparison, the crust, where all oceans reside, is only 30 km thick.
The new proposed model of water distribution directly impacts current estimates regarding the nature of exoplanets. Until now, to conclude the presence of water, planets are weighed, their atmospheres are reviewed, and their density is measured. So far, there has been no luck in finding oceans. However, this does not mean they do not have water. In fact, the authors of the study believe that the abundance of this resource could be up to 10 times greater than previously assumed. “Planets have much more abundant water than previously thought,” Dorn concludes in a press release.