The icy crust that protects Europa ’s ocean from the cold of space is at least 20 kilometers ( 12 miles ) thick , an analysis of data from the Galileo mission suggests . The close sheds no lighting on the question of whether that sea contains life , but indicates how arduous it will be to chance a conclusive answer .

grounds for an ocean inside Jupiter ’s moon Europa dates back to the Voyager spacecraft , with the Galileo mission strengthening the case . The uncovering inspired scientists and scientific discipline fable writers alike . We now acknowledge that many icy worldly concern in the outer Solar System deal this trait , but Europa remain of prime pursuit not just because it was the first . The rubble throw off from nearbyIo ’s volcanoesgives Europa the potential for more complex chemistry than other populace with internal ocean .

A possible obstacle to Europa ’s status as ground zero for exobiology research would be an to a fault thick crust . premature watching have not been able to ascertain how close to the control surface the liquid water system get ; efforts to do the question have produced estimate ranging from a few kilometers to 10 times that . By comparison , the sea within Enceladus , while much small and perhaps much younger , lam into distance throughgeysers at the south pole , providing an chance to sample it directly , as well as suggesting it might not be too hard to get asufficiently flexiblerobot down there .

Europa ’s surface is thesmoothest in the Solar System , thanks to the apparent movement of its trash , but it nevertheless bear some tincture of retiring impacts from outer space . A team led by MIT ’s Dr Shigeru Wakita realized two of these , known asTyre and Callanish , could be central to determining crustal heaviness .

Tyre and Callanish are both multiring basin . Wakita and co - authors model what would bechance with asteroid of appropriate sizing hitting crust of take issue heaviness and concluded only ice at least 20 kilometers stocky would ensue in something like what we see . The digit is a minimum ; Europa ’s crust may be a great deal thicker . If the crust is 15 kilometers ( 9 miles ) thick , multiring Crater of this size would be much deeper .

Europa ’s freshness may not be the same heaviness everywhere . Just as Enceladus ’s ocean is suppose to be much cheeseparing to the surface near the south pole than elsewhere , Europa may have regions of slender ice . The authors consider it unlikely the variation is large , and the similarity of the result they get at two locations does n’t favor the estimate we ’d just require to land a drilling rig in the right spot .

The generator also find that Europa ’s ice rink is composed of layers with different thermal properties . The outermost part , 6 - 8 km ( 3.7 - 5 mile ) buddy-buddy , is conductive , while below this lies comparatively warm convecting frappe .

late observations of the fundamental peaks within some of Europa ’s volcanic crater have been used as grounds the heat of the impacts did not melt all the way through to the ocean below . Using these craters ’ size , planetary scientists could calculate the heat energy generated , and therefore the crust must be at least 3 - 4 klick ( 1.8 - 2.4 miles ) heavyset , but this represented a minimum only . comparing of the conformation of small and orotund craters hint that the rigid frappe of the surface only gallop down around 7 kilometers ( 4.3 mile ) , without revealing whether it rests on soft ice , or directly on urine .

Mulitring craters are produced by a complex process in which an impacting object grow a shockwave and a serial publication of impermanent formations that collapse in turn , leaving behind a broad washbasin with surrounding rings . The extra chance created by this multistage process allow ice models to harness out various pre - existing conditions , including ice less than 20 km recondite .

Jovian moons Ganymede and Callisto are also thought topossibly moderate inner oceansbut with much thicker casing than Europa . The authors suggest thatpast estimatesof 80 - 105 km ( 50 - 60 miles ) may be considerably underestimating these moons ’ crustal heaviness .

The study is loose access inScience Advances .