7:30AM GMT 17 Nov 2011
An ice cavern containing as much water as the North American Great Lakes may provide a potential habitat for life on Jupiter’s moon Europa, scientists believe.
The salty “lake” is thought to be locked within Europa’s icy outer shell a few kilometres from the surface.
Other large pockets of liquid water are also likely to exist on the moon, it is claimed.
Scientists are excited by the discovery, which offers one of the best hopes yet of finding life beyond the Earth.
Evidence for the ice-covered lake in Europa’s Thera Macula region is seen in the shape of the terrain above it. The site appears to be marked by a fractured and collapsing “lid” of floating ice.
On Earth, similar features in the Antarctic are caused by briny seawater penetrating and weakening ice shelves. They are also present in Iceland, where glaciers are heated from below by volcanic activity.
Scientists have long suspected that a liquid or slushy ocean exists under Europa’s surface, warmed by the tidal forces of Jupiter’s powerful gravity.
Theoretically, a liquid water ocean could provide a suitable habitat for life – but only if it was not too far from the surface.
Experts disagree about how thick the layer of covering ice is. The new research, based on images from the Galileo probe, suggests that water “lenses” could lie as little as three kilometres below the bottom of the surface crust.
Lead scientist Dr Britney Schmidt, from the University of Texas, said: “One opinion in the scientific community has been, ‘If the ice shell is thick, that’s bad for biology – that it might mean the surface isn’t communicating with the underlying ocean’.
“Now we see evidence that even though the ice shell is thick, it can mix vigorously. That could make Europa and its ocean more habitable.”
The research, published today in the journal Nature, involved computer simulations based on observations of Europa and Earth.
Dr Schmidt’s team focused on two circular bumpy regions on Europa’s surface called “chaos terrains” .
The scientists produced a four-step model to explain the features which resolves several conflicting observations.
However, it can only infer the presence of the hidden lakes. Their existence will only be confirmed by a new space mission designed to probe Europa’s ice shell.
Such a mission, likely to employ ground-penetrating radar, is now under consideration by American space agency Nasa.
Commenting on the study, Dr Robert Pappalardo, senior research scientist at Nasa’s planetary science section, said: “It’s the only convincing model that fits the full range of observations. To me, that says ‘yes, that’s the right answer’.”