The habitability of Mars and other exoplanets orbiting a star’s habitable zone depends on a wide variety of factors, but one of the most fundamental may be size.
This is the conclusion of a study published in the Proceedings of the National Academy of Sciences which used stable isotopes of potassium in 20 confirmed Martian meteorites to estimate the presence, distribution and abundance of volatile elements. Isotopic composition is an indicator of more volatile elements and compounds such as water.
Researchers at Washington University in St. Louis have found a direct correlation between the levels of potassium isotopes and the size of the body in question. Mars lost more potassium and other volatiles than Earth during its formation, but retained more than the Moon and asteroid 4-Vesta.
“The fate of Mars was decided from the start,” said senior author Kun Wang, assistant professor of earth and planetary sciences at the University of Washington. “There is probably a threshold on the size requirements of rocky planets to hold enough water to allow habitability and plate tectonics, with a mass exceeding that of Mars.”
Study co-author Katharina Lodders called the correlation of isotopic compositions of potassium with a planet’s gravity “a new discovery with important quantitative implications for when and how differentiated planets received and lost. their volatile substances ”.
There is no doubt that water has flowed and accumulated on the surface of Mars, but the total amount is difficult to quantify through remote sensing and analysis of samples by surface rovers.
“There are many models for the bulk water content of Mars,” Wang said. “In some of them, early Mars was even wetter than Earth. We do not believe this is the case.
Co-author Klaus Mezger of the Center for Space and Habitability at the University of Bern in Switzerland said the study “points out that there is a very limited size range for planets to have just enough but not too much water to develop a habitable surface environment These results will guide astronomers in their search for habitable exoplanets in other solar systems.