Saturn's Geyser-Covered Moon Enceladus May Be Able to Support Life
Is Enceladus the best candidate for a life-sustaining planet? Data from the Cassini spacecraft reveals that water may be able to reach from the moon's underground sea all the way to its surface.
The research published in the Astronomical Journal details two previous studies that were foundational to these findings: in 2005, Cassini's cameras were able to map 101 geysers on the surface of Enceladus. These geysers erupted with ice particles and water vapor from "tiger stripe" fractures, distinctive geological features of Enceladus that are characterized by sub-parallel linear depressions. This was also the first of many studies to find a correlation between geyser and hot spot activity, but the direction of the causal relationship was long unknown. Some theorized that the frictional heat from the walls of the fractures rubbing together produced the geyser activity by melting ice into water vapor and liquid, while others theorized that the heat was caused by condensation of water vapor that originated below the moon's surface.
This question was answered by a 2010 study, in which further data from the Cassini confirmed that the hot spots were relatively small, only dozens of feet across. As a result, the size eliminated the possibility that they were caused by frictional heating, but was consistent with condensation. "Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa," said Carolyn Porco, leader of the Cassini imaging team from the Space Science Institute. "It also told us the geysers are not a near-surface phenomenon, but have much deeper roots."
Now, the Cassini is at it again, as further analysis of Enceladus gravity data has confirmed that the only logical source of the condensation is a subsurface ocean that lies underneath the planet's ice shell. Even more significantly, they found that small tunnels through the ice shell can remain open between the sea and the surface if they are filled with liquid water.
From the paper: "The coincidence of individual jets with very small hot spots... 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."
This study could have a wide range of implications, particularly in the search for an Earth-like planet that could possibly sustain life. While another Saturn moon, Europa, is generally at the forefront of this discussion as a result of its icy exterior and predicted potential for liquid water, in light of this data we may have to reconsider Enceladus as a primary candidate for terraforming and colonization.