The geysers of Saturn’s moon Enceladus have been counted and mapped, and the findings provide a small boost to speculation this is the best place to hunt for extraterrestrial life in the solar system.
Tidal flexing as a result of the interplay of Enceladus’ orbit and the gravity of Saturn and the moon Dione has melted part of Enceladus’ interior and created hot spots around its pole from which geysers sprout.
However, while this flexing is almost certainly the ultimate cause of the geysers, there is still mystery about the mechanisms. One theory holds that the flexing causes blocks of ice to rub against each other, generating frictional heat close to the surface. An alternative theory, much more conductive to life, is that boiling water from the depths rises up through fracture lines to become geysers at the surface.
By mapping the geysers and hotspots Dr Carolyn Porco of the Space Science Institute has shown that they coincide, both with each other and with locations for tidal stress. In The Astronomical Journal Porco reveals high resolution maps that match 10m wide hotspots to individual geysers. Frictional heating sites are expected to be much larger.
NASA/JPL-Caltech/Space Science Institute. A 3D model of 98 of Enceladus' geysers.
This, Porco claims, “strongly suggests that the heat accompanying the geysers is not produced by shearing in the upper brittle layer but rather is transported, in the form of latent heat, from a sub-ice-shell sea of liquid water, with vapor condensing on the near-surface walls of the fractures.” The paper provides evidence the geysers “are capable of opening water-filled cracks all the way down to the sea.”
This conclusion certainly does not prove that Enceladus hosts life. Nevertheless, it was the idea of connections between an internal sea the size of Lake Superior and surface vents that sparked interest in Enceladus as venue for life in the first place. Organic molecules have been found in the plumes, and if life does exist in the interior traces ejected into the plume might be the easier to find than anything deep beneath the surface of Mars or Europa.
A companion paper observed that the plume waxes and wanes in intensity in the course of Enceladus’ orbit, which is attributed to the opening and closing of the fractures, although there appears to be an unexplained delay to the eruptions.
NASA/JPL-Caltech/Space Science Institute. Artist's rendering of a cross-section of the ice shell immediately beneath one of Enceladus' fractures.