During its voyage around the ringed planet from 2004 to 2017, the Cassini spacecraft observed a surprising amount of geological activity on Saturn’s sixth largest moon, Enceladus. Cassini found that the frigid world not only has a vast global ocean lurking beneath its thick, icy shell, but also scores of geysers that routinely erupt from fissures in its surface, blasting plumes of mineral-laden water vapor into space at speeds of over 800 miles per hour.
However, the driving force behind this geologic activity has long been a mystery. Despite being only about as wide as Arizona, Enceladus is one of the brightest objects in our solar system. Since its ice-covered surface reflects almost 100 percent of incoming sunlight, the surface of Enceladus is also extremely cold, hovering around 330 degrees Fahrenheit below zero (-201 Celsius). Given its tiny size, icy crust, and frigid temperatures, one would expect that Enceladus would have cooled rapidly after its formation, freezing solid long ago. But this is apparently not the case.
How is Enceladus still so geologically active when its similarly sized neighbor, Mimas, seems to be completely frozen and dead? Shouldn’t the ocean beneath Enceladus’ icy crust have frozen solid billions of years ago? These questions, which have puzzled astronomers and planetary geologists for the past decade, may have finally been answered in a
paper published yesterday in
Nature Astronomy.
In the study, researchers presented the first computer model of Enceladus that not only replicates all of the moon’s fundamental characteristics as seen by Cassini, but also demonstrates an effective heating mechanism by which Enceladus could maintain its subsurface liquid ocean for billions of years.