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When the European Space Agency’s Philae lander arrived on the comet 67P/Churyumov-Gerasimenko – also called comet 67P – it bounced twice before reaching its final resting place. Now researchers have found the location of the second bounce, which exposed the strange ice beneath the comet’s surface.

The Philae lander was carried to 67P aboard the Rosetta orbiter, which launched in 2004 and arrived at the comet in 2014. When Philae was dropped to the surface, the harpoons designed to hold it in place didn’t fire, so the lander bounced. The location of the first bounce and the lander’s final resting place were both found, but we didn’t know where the second bounce took place until now.

“I think it’s one of the most positive things that happened on the mission, that it bounced, because we managed to get science from three locations on the comet,” says Laurence O’Rourke, a member of ESA’s Rosetta team. O’Rourke and his colleagues found the second bounce site by analysing pictures from Rosetta taken before and after Philae’s landing.

They found a bright streak across a pair of boulders in a region that O’Rourke nicknamed “skull-top ridge” because of its resemblance to a skull in some of the images. “It was like a chainsaw sliced through the ice,” he says. Philae appears to have bounced between the boulders, producing four slashes that revealed the primitive ice beneath the comet’s surface layer of dust.

Analysing those gashes allowed the researchers to calculate the strength of the ice, which they found is weaker than candyfloss. “This ice that’s 4.5 billion years old is as soft as the foam that’s on top of your cappuccino, it’s as soft as sea foam on the beach, it’s softer than the softest snow after a snowstorm,” says O’Rourke.

Knowing that some of the comet’s ice is so soft could help future landers find a safer place to touch down on 67P or other comets like it, he says. It could also be important for understanding how to protect Earth should a comet ever head our way. “You cannot just hit it with an object and expect it to move or disintegrate,” says O’Rourke. “It would be like punching a cloud.”

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