Excess heat is flowing from the north pole of Enceladus, hinting at a careful energy balance deep that may have kept the subsurface ocean stable over geologically significant timescales, boosting its suitability for life.
One of Cassini mission found giant plumes of water vapour squirting up from the ocean deep below through huge fractures in the surface. These plumes are powered by energy from tidal interactions with Saturn, which flex the moon's interior, subtly squeezing and stretching it and ultimately keeping its interior warm enough for liquid water.
The question of how long Enceladus' ocean has existed is an unanswered one, but with water, heat and the right organic chemistry for life, Enceladus is viewed as a prime target for the search for life beyond Earth.
"Enceladus is a key target in the search for life outside the Earth, and understanding the long-term availability of its energy is key to determining whether it can support life," said study leader Georgina Miles, of the Southwest Research Institute and a Visiting Scientist at the University of Oxford, in a statement.
If Enceladus didn't continually receive enough energy from tidal heating, its ocean would gradually freeze. If it received too much energy, the activity in the ocean would increase, altering its environment perhaps to the detriment of its habitability. Therefore, a careful balance between the energy deposited into the moon by the tidal interaction, and the energy that leaks away through convection up to the surface and into space, is required to ensure stability over hundreds of millions or even billions of years.
Planetary scientists know that heat flows out from the south pole, where the fractures, known as tiger stripes, that produce the plumes are located. However, they thought that Enceladus' north pole was inert.
It seems that they were wrong.