Old ice beneath the surface of Comet 67P is softer than cotton candy

By Leah Crane

An illustration of the Philae lander on Comet 67P

ESA / ATG Medialab

When the European Space Agency's Philae lander landed on Comet 67P / Churyumov-Gerasimenko – also known as Comet 67P – it ricocheted off twice before reaching its final resting place. Now researchers have found the location of the second jump that exposed the strange ice beneath the comet's surface.

The Philae lander was brought to 67P aboard the Rosetta orbiter, which launched in 2004 and arrived at the comet in 2014. When Philae fell to the surface, the harpoons that were supposed to hold him in place didn't fire, causing the lander to ricochet. The location of the first jump and the lander's final resting place were both found, but we didn't know where the second jump took place until now.

"I think one of the most positive things that happened on the mission is that it ricocheted off because we managed to get science from three places on the comet," said Laurence O'Rourke, a member of the Rosetta team the ESA. O’Rourke and his colleagues found the second jump point by analyzing images of Rosetta taken before and after Philae landed.

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They found a bright streak over two boulders in a region that O’Rourke called the "skull crest" in some pictures because of its resemblance to a skull. "It was like a chainsaw cut through the ice," he says. Philae appears to have jumped between the boulders, creating four slashes that revealed the primitive ice beneath the comet's dusty layer.

By analyzing these cuts, the researchers were able to calculate the strength of the ice, which is weaker than cotton candy. "This 4.5 billion year old ice cream is as soft as the foam on your cappuccino, it is as soft as sea foam on the beach, it is softer than the softest snow after a blizzard," says O & # 39; Rourke.

Knowing that part of the comet's ice is so soft could help future countries find a safer place to touch down on 67P or other comets like this one, he says. Understanding how the earth can be protected should a comet ever come our way may also be important. "You can't just hit it with an object and expect it to move or disintegrate," says O’Rourke. "It would be like hitting a cloud."

Journal reference: Nature, DOI: 10.1038 / s41586-020-2834-3

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