In our search for life in the Solar System, there are a few places that look rather promising. Mars, which once had oceans on its surface, may have signs of past or present life. Jupiter’s moon Europa, meanwhile, with an underground ocean, could be hiding something beneath its surface.
But Saturn’s moon Enceladus, too, is high up the list. This is because, like Europa, we also think it has a subsurface ocean. However, estimates had suggested its ice sheet was upwards of 60 kilometers (37 miles) thick in places, making it almost impossible to access with current technology.
Well, that might not be the case anymore. An international team of researchers that includes scientists from the French National Centre for Scientific Research (CNRS) has suggested that, in places, the ice sheet may be only a few kilometers thick. If true, this would suggest the ocean of Enceladus is tantalizingly close to the surface.
Their study, published in Geophysical Research Letters, looked at the libration of Enceladus, which is the “wobble” in its rotation. This wobble had been linked to tidal effects on the moon, suggesting its ice shell had an average thickness of 20 kilometers (12 miles), but this was “inconsistent with other gravity and topography data,” the CNRS said in a statement.
To solve this, the researchers think that the top 200 meters (660 feet) of ice on Enceladus acts as an elastic shell. They suggest Enceladus has a rocky core 370 kilometers (230 miles) wide, with the ocean located about 45 kilometers (28 miles) underground. Their model suggests the ocean makes up almost half of the moon’s volume, 40 percent, with a salt content similar to Earth’s oceans.
But most excitingly of all, they say that, while the ice shell does have an average thickness of 20 kilometers, at the South Pole it is just 5 kilometers (3 miles) thick. We don’t have the means to drill down under this ice yet, but there are a few missions in the works – such as the Enceladus Life Finder – that will lay the groundwork for future missions to possibly do this.
And according to this study, if the ice sheet is that thin, it means the push and pull of Saturn’s gravity is not enough to explain how Enceladus stays warm, as a thinner ice sheet traps less heat.
“The model therefore reinforces the idea that there is strong heat production in Enceladus's deep interior that may power the hydrothermal vents on the ocean floor,” the statement adds. “Since complex organic molecules, whose precise composition remains unknown, have been detected in Enceladus's jets, these conditions appear to be favorable to the emergence of life.”
Exciting times indeed.
Image in text: Thickness of Enceladus’ ice sheet. Yellow denotes 35 kilometers (22 miles), and blue (South Pole) is less than 5 kilometers (3 miles). © LPG-CNRS-U. Nantes/U. Charles, Prague.