Failed probe’s crash landing reveals the softer side to comet

‘This not only informs us about the gaps in Philae’s journey, but about the nature of the comet’

AS LANDINGS go, it was a graceless entry into another world. In November 2014, the little space probe Philae hit comet “67P/ Churyumov- Gerasimenko”, bounced a mile into the air, then tumbled across the surface, finally coming to rest at the bottom of a cliff.

Now scientists at the European Space Agency have pieced together Philae’s final path, and found that as the probe skipped across the comet’s surface boulders it sliced away rock and dust to reveal the strange, ancient ice beneath.

Unexpectedly, the ice was incredibly soft, a discovery that should help scientists improve future landing attempts.

“That the comet has such a fluffy interior is really valuable information in terms of how to design the landing mechanisms, and also for the mechanical processes that might be needed to retrieve samples,” said Matt Taylor, ESA’S Rosetta project scientist. This not only fills in the gaps in the story of Philae’s bouncy journey, but also informs us about the nature of the comet.”

Philae was part of the ESA’S Rosetta mission, which aimed to make the first soft landing on a comet. It launched in 2004, eventually arriving at “67P” in 2014, when it was travelling between Mars and Jupiter. The probe was released from the Rosetta spacecraft on Nov 12, equipped with a thruster and two harpoons to anchor it to the touchdown site, called Agilkia.

However, the thruster failed to fire and the anchors did not deploy correctly, leaving the probe to bounce away from the surface and embark on a two-hour flight, during which it collided with a cliff edge and hurtled towards its second touchdown location.

Philae eventually came to a halt in a sheltered spot that was only identified in Rosetta imagery 22 months later.

Laurence O’rourke, a scientist at the ESA, who played the leading role in finding Philae, was also keen to discover a second touchdown site. “It was important to find the touchdown site because sensors on Philae indicated that it had dug into the surface, most likely exposing the primitive ice hidden

‘This mixture is fluffier than froth on a cappuccino’

underneath, which would give us invaluable access to billions- of-years- old ice,” he said.

A reanalysis of the touchdown data found that Philae had spent nearly two full minutes at the second touchdown site, making at least four distinct surface contacts as it ploughed across it.

One particularly notable imprint revealed in the images was created as

Philae’s roof sank 10in into the ice on the side of a crevice. “The simple action of Philae stamping into the side of the crevice allowed us to work out that this ancient, billions-of-years-old, icy-dust mixture is extraordinarily soft – fluffier than froth on a cappuccino, or the foam found in a bubble bath,” said Mr O’rourke. The research was published in the journal Nature.