Europa’s frozen surface is covered with distinctive pairs of ridges that straddle ice channels. These double ridges are the most common features on the Jovian moon. But scientists still don’t have a clear idea of how oddities are created.
Now, an analysis of images of a similar set of ridges on the Greenland ice sheet suggests that relatively shallow water within Europa’s thick icy shell may be behind its formation, scientists report April 19 in nature communications. If so, that could mean that Europa has a lot more shallow liquid water than scientists thought.
Europa’s double-ridge systems, which can stretch hundreds of kilometers, include some of the oldest features on the moon, says Riley Culberg, a geophysicist at Stanford University. Some researchers have proposed that the flexing of the moon’s icy shell due to tides in an ocean of underlying liquid water plays a role in the formation of the cristae (Serial number: 8/6/20). However, others have suggested that water welled up from deep within the icy moon, a process known as cryovolcanism, to create the ridges. However, without a closer look, it has been difficult to nail down a more robust explanation.
But Culberg and his colleagues appear to have taken a breather. Data collected by NASA’s ICESat-2 satellite in March 2016 showed a 800-meter-long double-ridge system in northwestern Greenland. So the team looked back at other images to see when the ridge system first appeared and to assess how it grew. The researchers found that the ridges appeared in images taken from July 2013 and are still there today.
When the ridges, found on either side of a channel like those in Europe, reached full size, they averaged just 2.1 meters in height. That’s much smaller than the ridges of Europa, which can rise 300 meters or more from the moon’s surface. But surface gravity is much lower on Europa, so the ridges can grow much larger there, Culberg says. When he and his colleagues factored in the difference between Earth’s and Europa’s gravity in their calculations, they found that the ratios of the two ridge systems are consistent.
Scientists will never get a perfect analog of Europa on Earth, but the Greenland ridges “look like the ridges of Europa,” says Laurent Montési, a geophysicist at the University of Maryland in College Park who was not involved in the study.
Data from aircraft-mounted radar collected in March 2016 show that a water-filled snow cover about 10 to 15 meters below the surface underlies Greenland’s ridges, Culberg and his team say. That water comes from surface meltwater that sinks and is then collected in buried snow, which in turn sits on top of an impermeable layer of ice.
The repeated cycles of freezing and thawing of the water in that snow cover would push the water up to the surface, the researchers propose. In the first stage of refreezing, a solid plug of ice forms. Then, as more water freezes, it expands and is forced to the surface on either side of that plug, pushing the material up and producing the double ridges on the surface.
In Europe, the process works the same way, the researchers suggest. But because there is no known meltwater or precipitation on the moon’s surface, the near-surface water would probably have to come from the ocean believed to be trapped under the icy shell of the moon (05/14/18). Once the water rose to the surface through the cracks, it could accumulate in thick ice sheets broken up by tidal flexing or meteorite impacts.
“There is a general consensus that these ridges grow from cracks in the ice,” says William McKinnon, a planetary scientist at Washington University in Saint Louis, who was not involved in the study. “But as if they do is the question”.
The answer to that question may not be long in coming, says McKinnon. NASA’s Europa Clipper mission is scheduled to launch in late 2024. If all goes well, the orbiter will reach Jupiter in April 2030. “If something like what happened in Greenland is happening in Europa, we will be able to see it. ,” he says.
The researchers will also be interested in seeing if the mission can determine what kinds of materials might have been brought to Europa’s surface from the deep ocean, because the moon is considered one of the best places in the solar system. to search for extraterrestrial life (Serial number: 4/8/20).