IIt’s hard not to like Europa. It is by far the most promising of Jupiter’s 79 moons, covered in a layer of water ice about 30 km (18 mi) thick. Beneath the ice is a salty ocean enclosing the globe which astronomers believe could be up to 150 km (93 mi) deep. As its larger sister moons – Io, Ganymede, and Callisto – pass through their orbits, their gravity bends Europa slightly, generating an interior heat that keeps the water from freezing. Give a warm, salty, amniotic ocean like that a few billion years, and it’s unclear what kind of life it might create.
The problem has always been that even if NASA could land a probe on Europa, it would have to drill through that 30km ice crust to sample what lies beneath. However, a study published Tuesday in Nature Communication suggests that liquid water could exist in lakes and pools much closer to the surface of Europa, where a spacecraft could more easily reach it. These tantalizing findings come not from studying Europa itself, but from a much more familiar – and decidedly more accessible – place: Greenland.
Of all the features that mark the surface of Europa, none is so common as its network of double ridges. Essentially a series of criss-crossing indentations in the moon’s surface, each several hundred kilometers long, they take the form of twin ice berms with ridges up to 304 m (1,000 ft) high, separated by valleys of about 0.8 km (0.5 mi). large.
NASA currently has no spacecraft monitoring Europe, but it regularly flies over Greenland by plane, taking photos and radar surveys of the ice to study the effects of climate change. During one such pass, the cameras captured a double ridge nearly identical, though smaller, to those found on Europa. Radar data showed that the gouge in the ice was formed by water seeping in from below, collecting in cavities within the ice and refreezing. The water expands when it freezes, which has caused both the ice to crack and the berms to rise.
This simple piece of hydrology has big implications for Europa, the paper’s authors conclude. If its double ridges are formed in the same way, it means that water from the subterranean ocean is also forced to the surface there, not accumulating 30 km down, but only a kilometer or two into the ice cap. Additionally, when the ice would initially crack, the water would be exposed to chemistry on the surface, which includes sulfur and oxygen from volcanoes on nearby moon Io, as well as methane, carbon, nitrogen and hydrogen carried by meteorites that may have collided with the surface. This prebiotic material could be a recipe for life in underground pools.
“Water penetrating to the surface would be a way for chemicals to seep in,” Riley Culberg, a Stanford University doctoral student and the paper’s lead author, said in an email to TIME.
If near-surface pools exist on Europa, we should know soon. In 2024, NASA sends the Europa Clipper to the Jovian system to closely study the icy moon; powerful ice-penetrating radar will look for pockets of water. The next step – although NASA doesn’t have a specific date yet – is a proposed Europa lander that would study the surface ice and drill at least halfway through it, sampling its chemistry.
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