Ancient ice beneath the surface of comet 67P is softer than candyfloss

 When the EU 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 placement 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 fell upon the comet in 2014. When Philae was dropped to the surface, the harpoons designed to carry it in situ didn’t fire, therefore the lander bounced. the situation of the primary bounce and therefore the lander’s final resting place were both found, but we didn’t know where the second bounce materialized until now.

“I think it’s one in all the foremost positive things that happened on the mission, that it bounced because we managed to induce 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 analyzing pictures from Rosetta taken before and after Philae’s landing.

They found a bright streak across a pair of boulders during a region that O’Rourke nicknamed “skull-top ridge” due to its resemblance to a skull in a number of the pictures. “It was sort of a chainsaw sliced through the ice,” he says. Philae appears to own bounced between the boulders, producing four slashes that exposed the primitive ice beneath the comet’s surface layer of dust.

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