by A ridge carved into the Greenland ice sheet provides an unexpected clue that many pockets of water could be trapped just below the surface of Europa, the ice-covered moon of Jupiter, one of the most likely candidates to host the microbial life of the solar system.
The area of Europeone of Jupiter, is covered in a 15-mile-thick (20-kilometer) crust of ice, under which scientists believe an ocean rocks. But there could be scientific promise much closer to the surface of the frozen moon, according to a new study that has found similarities between the processes shaping the surface of the distant moon and Earthis the very own icy Greenland.
Europe’s ice crust is lattice-like with so-called double ridges, pairs of long parallel raised lines with a valley in between, up to hundreds of miles or kilometers long. Every sector of the moon’s surface is marked by a criss-crossing network of these double ridges, but scientists have never been entirely sure of their formation.
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But a recent analysis of satellite images has revealed that a strikingly similar ridge formed in the ice sheet covering Greenland around 10 years ago.
“This is the first time we’ve seen a double ridge like this on Earth,” Riley Culberg, a graduate student at Stanford University and lead author of the new study, told Space.com.
Studying what lies beneath this double ridge in Greenland, Culberg and his colleagues hypothesize that the double ridges – both on Earth and on Europa – are formed by groundwater rising through fissures in the surface ice, then refreezing. If the explanation is correct, it’s a hint that Europa might have more than just a hidden deep ocean; the Jovian moon could also contain water in pockets just below the surface of the ice.
Culberg, a geophysicist who primarily studies the impacts of climate change on the Greenland ice sheet, saw images of the double ridges of Europa and instantly recalled a feature he had seen in the images of the polar island of the earth. Indeed, when scientists adjust their measurements to account for the different gravity, the shape of Greenland’s double ridge is strikingly similar to that of Europe.
This is useful because scientists can do something in Greenland that they cannot yet do in Europe: break through the ice sheet using radar. And in Greenland, radar scans showed water that had gushed out from under the double ridge.
Scientists believe that upwelling is the key to the formation of double ridges. When a pool of water forms in the ice, it can begin to create pressure against the surface ice above. With enough pressure, the ice can crack and water can begin to flow into the space. This water rapidly refreezes, but the pressures of this whole process are carving double ridges into the surface.
It’s hard to overstate how Europe is covered in double ridges. If the proposed explanation is correct, it would mean that pockets of water below the surface have been a feature of Europa for much of the moon’s history. If so, something has to replenish the water pockets.
This is where Greenland is not such a good comparison, since its double ridge has formed over the past decade. Culberg and his colleagues believe an unusually hot summer in 2012 melted enough water to collect in an underground pocket below the ridge.
But there is little meltwater on the surface of Europa, so Culberg and his colleagues have argued that this new water is coming from even deeper under the ice: tens of miles or miles deep there. where scientists expect to find a global ocean.
“That at least tells us that there may be a lot of cycling between the subsurface ocean and the near surface,” Culberg told Space.com.
Finding these shallow pockets of water could be a quest for future probes to Jupiter’s moon, like NASA’s European Clipper mission, set to launch in 2024. And exciting for scientists like Culberg, Europa Clipper will carry an ice-penetrating radar, just like the type researchers used to peer under Greenland.
Culberg and his colleagues published their work in the journal Nature Communications on April 19.
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