Europe may have much more shallow running water than scientists thought

The frozen surface of Europe is covered with characteristic pairs of reefs that stretch through ice beds. These double ridges are the most common features of the Jovian Moon. But scientists do not yet have a clear idea of ​​how the oddities arise.

Now, an analysis of images of a similar series of reefs on Greenland ‘s ice sheet suggests that relatively shallow water within Europe’ s thick ice sheet may be behind their formation, scientists report. Communications in nature. If so, it could mean that Europe has much more shallow running water than scientists thought.

Europe’s double-reef systems, which can stretch for hundreds of kilometers, include some of the oldest features on the moon, says Riley Culberg, a geophysicist at Stanford University. Some researchers have suggested that bending the moon’s ice sheet due to tides in the ocean with liquid plays a role in reef formation (SN: 6.8.20). Others suggest that water erupted from the depths of the ice moon – a process known as cryovolcanism – to create reefs. Without a better view, however, it was difficult to find a firmer explanation.

But Culberg and his colleagues seem to have taken a break. Data collected by NASA’s ICESat-2 satellite in March 2016 showed an 800-meter-long double reef system in northwest Greenland. Therefore, the team looked at other images to see when the reef system first appeared and to assess how it grew. Researchers have found that the reefs appeared in images taken back in July 2013 and are still there today.

When the ridges – which lie on either side of the riverbed, like those in Europe – reached full size, they were on average only 2.1 meters high. It is much smaller than the reefs in Europe, which can rise 300 meters or more than the lunar surface. But surface gravity is much lower in Europe, so the reefs there can become much larger, Culberg says. When he and his colleagues considered the difference between Earth’s and European gravity in their calculations, they found that the proportions of the two reef systems were consistent.

Double ridge systems are common in Europe. The largest pair seen in this composite image of NASA’s Galileo spacecraft in the 1990s is about 2.6 kilometers wide and 300 meters high.JPL-Caltech / NASA, ASU

Scientists will never get a perfect analogue of Europe on Earth, but the reefs in Greenland “look just like European reefs,” says Laurent Montési, a geophysicist at the University of Maryland at College Park who was not involved in the study.

Data from radar installed in the aircraft collected in March 2016 show that a layer of snow filled with water about 10 to 15 meters below the surface lies below the Greenlandic reefs, say Culberg and his team. This water comes from surface melted water that sinks and then collects in the buried snow, which in turn sits on top of an impermeable layer of ice.

Repeated cycles of freezing and thawing water in that layer of snow would push water toward the surface, the researchers suggest. In the first phase of re-freezing, a solid plug of ice is formed. Then, as more water freezes, it expands and pushes toward the surface on either side of that plug, pushing the material upward and creating double ridges on the surface.

In Europe, the process works the same way, researchers suggest. But since there is no known dissolved water or precipitation on the Moon’s surface, water near the surface would probably have to come from an ocean thought to be trapped beneath the moon’s ice sheet (5/14/18). Once that water rises toward the surface through cracks, it could gather into thick layers of ice shattered by tidal bending or meteorite blows.

“There is a general consensus that these reefs grow out of cracks in the ice,” says William McKinnon, a planetary scientist at the University of Washington at St. Louis who was not involved in the study. “But how Whether they do that is a question. “

The answer to that question may not wait long, McKinnon says. NASA’s Europa Clipper mission is scheduled to launch in late 2024. If all goes well, the orbiter will arrive on Jupiter in April 2030. “If something similar happens in Greenland happening in Europe, we’ll be able to see it,” he says.

Researchers will also be interested to see if the mission can determine what kind of material could be brought to the surface of Europe from the ocean deep below, as the Moon is considered one of the best places in the solar system to search for extraterrestrial life (SN: 8.4.20).

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