Unfortunately, our knowledge of life testifies to its integral dependence on water. Astronomers and astrobiologists come from this simple fact, focusing on finding exoplanets that can exist a liquid water sphere. Water tanks can be located on the surface of the planets, where heat from the host star holds water in the liquid state. But the possibility of existence of internal liquid oceans hidden under a thick layer of ice is not excluded.
The new analysis of NASA indicates that out of the 17th exoplanet, the inner oceans, hidden under the ice cover, may possess. These worlds, similar to Jupiter's ice satellites, can represent an object to find biosignatures - chemical traces of life.
Although the composition of these worlds remains mysterious, the temperature estimates of their surface obtained by previous studies indicate their significant coldness compared to the Earth. In addition, their density is less than in the Earth, despite the same size.
"Our analysis indicates that the surface of these 17 planets can be covered with ice, but they can receive enough inner heat from radioactive decay and tidal forces caused by the star to keep the internal liquid oceans," - says Linna Kvik from the center of space flights named after Goddard NASA.
In other words, although the host stars cannot provide enough heat to keep the water in the liquid state on the surface of these planets, the processes occurring in their depths can provide internal heat. For example, gravitational interactions with a star can lead to stretching and compression of rocks inside the planet, providing a considerable amount of inner heat - sufficient to support the inner oceans. The breakdown of radioactive elements in the planet's nucleus can also contribute to the inner heat.
"In connection with internal heating, all planets in our study can demonstrate cryovulcanic eruptions in the form of geyser -like loops," Kvik adds.
The study is based on knowledge of geyser activity of two satellites of Jupiter - Europe and Encelad. Two exoplanets, which are named in this study - Proxima Centaur B and LHS1140 B - proved to be particularly promising candidates for the presence of internal oceans near the surface.
