A new study of data collected during a 2011 Cassini flyby of Saturn’s moon Enceladus indicates its south polar region is warmer beneath the icy shell than previously thought, and its subsurface ocean may be not lie far underneath that surface.
Since 2005, NASA’s Cassini orbiter has revealed Enceladus’s south pole to be a highly active region, with plumes of water and ice venting through four tiger-striped surface fractures.
The plumes’ salty water content support the notion that a subsurface liquid water ocean interacts with Enceladus’s rocky core, behaving much like the underground ocean on Jupiter’s moon Europa.
Cassini flybys of Enceladus have focused on studying the moon’s interior to better understand its structure.
In the new study, researchers use microwave observations of Enceladus’s south pole taken by Cassini in 2011 to determine that heat is produced over a broad area of the south polar region and transported beneath the icy crust.
These findings suggest the subsurface ocean could be only several kilometers beneath Enceladus’s surface.
Only one high-resolution observation was conducted in microwave wavelengths over the south pole due to constraints on the Cassini mission, noted Alice LeGall of the Laboratoire Atmospheres Milieux, Observation Spatiales (LATMOS) and the Universite Versailles Saint-Quentin(UVSQ), both in France.
LeGall is lead author of a study on the findings published in the journal Nature Astronomy and an associate member of Cassini’s RADAR instrument team.
“These observations provide a unique insight into what is going on beneath the surface. They show that the first few meters below the surface of the area we investigated, although at a glacial 50-60 K (degrees Kelvin), are much warmer than we had expected: likely up to 20 K warmer in some places,” she said.
The warmer temperatures cannot solely be the result of tidal heating from Saturn and warmth from the Sun.
There appears to be a warm area beneath the frost layer at Enceladus’s south pole, which the researchers observed in microwave wavelengths.
Le Gall and her colleagues studied only a narrow arc-shaped area about 500 km long and 25 km wide, located approximately 30-50 kilometers north of the famous “tiger stripes.”
“The thermal anomaly we see at microwave wavelengths is especially pronounced over three fractures that are not unlike the tiger stripes, except that they don’t seem to be the source of jets at the moment,” Le Gall stated.
Their presence above a warm subsurface ocean indicates this region may have experienced varying levels of geological activity over time.
According to the researchers, heating cycles in this region are likely linked to Enceladus’s eccentric orbit around Saturn, which causes deformation and compression of the crust, producing fractures, while warming up the interior.
Because the ice at the south pole is thinner, it is subject to greater tidal deformation that produces more heat and keeps the underground ocean warm.