Saturn’s moon Enceladus is covered in dense snow. In some places the fluffy material is 700 meters high, new research suggests.
“It’s Buffalo, but worse,” says planetary scientist Emily Martin, referring to New York City’s famous snow. Snow depth suggests that Enceladus’ dramatic plume may have been more active in the past, Martin and colleagues report on Mar. 1. Icarus.
Scientists have been fascinated by the planet’s Enceladus geysers, made of water vapor and other materials, since the spacecraft spotted them in 2005.SN: 12/16/22). It probably comes under a smooth shell of salt spray.
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Some of that water goes to one of Saturn’s rings (SN: 5/2/06). But it mostly falls on the surface of the moon like snow, as Martinus says. Understanding the properties of that snow—its thickness and how thick and dense it is—could help reveal Enceladus’ history and lay the groundwork for future missions to this moon.
“If you call a robot out there, you have to understand what’s going to happen to the port,” said Martin, of the National Air and Space Museum in Washington, DC.
To find out how dense the snow on Enceladus is, Martin and his colleagues looked at Earth — specifically Iceland. The hosts of the island’s regions are characterized by geological features called chain pits, which are lines of pockmarks formed on the ground when loose debris, such as rocks, ice or snow, sinks into the crevice below (SN: 10/23/18). Similar features show up all over the solar system, including Enceladus.
Previous work suggested a method of using geometry and the angle at which the sun hits the surface to measure the depth of pits. That measurement can then reveal the depth of the material pits in the seat. A few weeks in the field in Iceland in 2017 and 2018 convinced Martino and his colleagues that they would do the same thing on Enceladus.
Using images from Cassini, Martin and colleagues found that the density of snow varies across the surface of Enceladus. It is hundreds of meters high in most places and 700 meters high at its thickest.
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It’s hard to imagine how all that snow got there, though, Martin says. If the precipitation was always what it is today, it would take 4.5 billion years — the entire age of the solar system — to deposit much snow on the surface. And then, too, the most fluffy snow.
Martins says that in the moment the moon was formed and never changed, it seems to have changed its features. If it had done so, the later layers of snow would have compressed the upper layers, making the whole layer compact and much less deep than it is today.
“I don’t think we’re going to do it for 4.5 billion years,” Martin said. But the feature could have been much more active in the past. “We don’t need to do it in a much shorter timeframe. You need to crank up the volume at the top.”
It’s a clever technique, says Shannon MacKenzie of Johns Hopkins University’s planetary science physics laboratory in Laurel, Md. Without pirates or astronauts on the ground, there is no way to scoop up the snow and see how far it has gone. The authors, however, cleverly using geology, as batillas, to be brooms.
MacKenzie was not involved in the new work, but was leading a mission concept study for an orbiter and lander that could one day visit Enceladus. One of the major problems in the study was where the lander could reach safely. “The key to the discussions was, what do we expect the surface to be?” says. A new paper could help identify “places that are too hairy to land on.”
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