Under the icy crust of cold exo-Earths, there may be liquid water and life, even if they are outside of the traditional habitable zone. An article about this was published in Nature Communications.
Astrobiologists traditionally distinguish a habitable zone – a series of orbits around a star that the planet should be able to support life. Since the key parameter for life is the presence of liquid water, the planet must be hot enough for the water to melt, but not hot enough for it to evaporate. This range is quite narrow, and many Earth-like planets are in the freezing zone.
Scientists from Rutgers University made calculations and concluded that such planets may still have liquid water. For him, the source of heat is not the star, but the core, and in this case the atmospheric pressure becomes insignificant. Melting can also occur due to the pressure and friction of ice against each other and against the rock bottom. The authors note that even a weak geothermal flow like that formed on the Moon can provide sufficient heat.
The water in such oceans interacts with the rocks and exchanges chemicals with them and is also shielded from radiation. Both of these factors are important to life. The situation is complicated on super-Earths, whose gravity is much greater than Earth’s. Water ice can form 18 different modifications when exposed to higher pressure and different temperatures, and different ice modifications can form layers that hold water together.
This effect is particularly important for red dwarf systems whose classical habitable zone is very close to the star. The planet is therefore subject to tidal capture and excessive exposure to the solar wind, which negatively affects habitability. Therefore, if life is possible outside of this region, this would significantly expand the search space for astronomers.