Aerospace engineer Luciano Iess and his group at the Sapienza University of Rome have described an under-ice sea the size of Lake Superior at the south pole of Enceladus. It extends to the mid-southern regions of Saturn’s 500-km moon, and is the source of its geysers, spurting salty water 500 km into space and gathering to form the faint E ring around Saturn.
Dramatic plumes, both large and small, spray water ice out from many locations along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus. (Photo credit: Wikipedia)
Iess’ group mapped the interior of Enceladus by looking at Doppler shifts as Cassini orbited the moon, thus tracking changing in the rocket’s speed due to gravitational changes. Results were reported April 4 in Science and summarized May 3, 2014 by sciencenews.org.
In 2004, Cassini discovered geysers of salty “water ice” spurting out of Enceladus’s south pole. Irwin and Schulze-Makuch’s book Cosmic Biology published pictures of the leaking “tiger stripes,” trenches 2 km wide and up to 150 km long, 35 km apart at the south pole, probably slip faults in the moon’s icy crust, estimated to be 30 to 40 km thick.
Iess agrees with Cosmic Biology that there could be interesting chemistry where “seawater meets rock.” Since the fissures creating the geysers expand and contract with Saturn’s tides and are up to 40 km long , there is a lot of surface area available for life to develop.
If the moon’s rocky core is warmer than the surface, as reported by Cosmic Biology (-100 degrees C. at the south pole), there could also be a heat gradient available along the fissures. The rock-water surfaces of the 10 km-deep ocean most amenable to life include the ice roof and the rocky ocean floor provided by the moon’s core, where some heat seems to be available.
Other considerations for life on Enceladus include possible exchanges with Titan and the methane, carbon monoxide and sodium detected in the geysers’ salt water. For common life based on carbon, solvent water and energy from light and chemicals, Enceladus can be included in the hopefuls since it provides a variety of habitats. Life there might even be moderately complex life, though it probably stayed simple and immobile, with limited cognition in such a dark place.
When the Tandem mission arrives in 2030 and samples the geysers, we may have some of the answers to some questions. How long has the lake existed? Something might have had time to evolve if the lake is as old as Enceladus itself. How long has the lake been leaking? Does the interiors ice maintain the lake’s volume of water? How smooth are the fissure surfaces? Rough enough for life to hide in?
How would the expulsion of salt water/ice affect any life forms, especially those hanging on in the fissures? Does the leaking mist contain any nitrogen? Is there any hope that clever RNA has done something interesting? (See my previous blog.) What about solvents other than water? Stay tuned and hope Tandem collects something of interest.