New observations from the Cassini space probe indicate that a vast ocean could exist beneath Dione's ice crust. Earlier, the same seas were found under the surface of two other moons of Saturn - Titan and Enceladus.
The data collected by Cassini was analyzed by a team of astrophysicists from the Royal Observatory of Belgium. Scientists report that the ocean can be hidden at a depth of about 100 km under the icy surface of Dione. In general, it resembles the neighboring satellite Enceladus, not so large, but much better known for the spectacular eruptions of geysers at its poles - it was they who indicated the presence of an ocean. No geysers are visible on Dione today, but cracks in its crust indicate similar activity in the past. Mikael Beuthe and his colleagues talk about this in an article published in Geophysical Research Letters.
The authors have modeled the icy surface of Dione and Enceladus - “global icebergs” that cover the entire satellites, floating on the surface of the global ocean. Evaluating the visible ice landscape of the satellite, the model calculated the required power of the support supporting it. Previously, such work made it possible to estimate the thickness of the crust of Enceladus and confirm the presence of fluid under it, but for Dione such calculations indicated the complete absence of a "secret" ocean. However, this time Bote and co-authors took into account one more important point - stress stresses arising in the ice crust. Their accumulation does not allow them to maintain their shape and causes fractures and cracks.
According to Belgian scientists, the new factor forces us to re-evaluate the thickness of the crust of Enceladus itself - it may turn out to be much more modest than previous versions, and in the circumpolar areas where geysers hit, not exceed several kilometers. This is also confirmed by the measured librations of Enceladus while moving in orbit, which oscillates like a bag filled with water in flight. The magnitude of the fluctuations also indicates a relatively thin crust. According to Bote and his colleagues, there is a place for the ocean on Dion.
Like Enceladus, Dione sways in motion, albeit too faintly and unnoticed for Cassini's instruments. However, the ocean on a satellite could have existed for its entire long history, and, of course, a relatively warm and liquid environment may well be suitable for life. However, it is more accessible on Enceladus, and on Titan, the seas of liquid hydrocarbons do splash right on the surface. So if the search for microbes in the Saturn system ever begins, Dione will have to wait for her turn.
Sergey Vasiliev