The most habitable region for life on Mars? Several miles below its surface, thanks to the underground melting of thick sheets of ice induced by geothermal heat. This is the hypothesis of a study conducted by Rutgers University and published in Science Advances .
One hypothesis that could help overcome the paradox of the young Sun weak .
Our star is, in fact, a huge nuclear fusion reactor that generates energy by melting hydrogen and transforming it into helium. Over time the Sun has gradually illuminated and heated the surface of the planets in our solar system. About 4 billion years ago, however, the Sun was much weaker, so the climate of the first Mars should have been freezing. However, the surface of Mars has many geological markers , such as ancient river beds, and chemical markers, such as water-related minerals, which suggest that the red planet had abundant liquid water in the so-called Noachian hero, from about 4.1 billion to 3.7 billion years ago. This apparent contradiction between geological analysis and climate models is called the weak young Sun paradox.
On rocky planets such as Mars, Earth, Venus, and Mercury, heat-producing elements such as uranium, thorium and potassium generate heat via radioactive decay. In such a scenario, liquid water can be generated by the melting at the bottom of thick sheets of ice, even if the Sun was weaker than it is now. On Earth, for example, geothermal heat forms subglacial lakes in the areas of the West Antarctic ice sheet, Greenland and the Canadian Arctic. A similar melting is likely to help explain the presence of liquid water on cold, freezing Mars 4 billion years ago.
The authors of the study examined various datasets on the fourth planet to see if warming by geothermal heat would have been possible in the Noachian era, data that confirmed the existence of the necessary conditions for the melting of the ancient subsoil ice. Mars. But even if the red planet had a hot and humid climate 4 billion years ago, life, if it ever originated, may have only developed in liquid water at progressively greater depths, because liquid water may have been stable. only at great depths due to magnetic field loss , atmospheric thinning and consequent drop in global temperatures.
In short, for the authors of the study only at great depths could life have been sustained by hydrothermal activity and therefore only the subsoil could represent the longest living environment on Mars.