“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.”
Dr Taylor believes that even if the harpoons have fired, they may not have been able to embed in the fluffy surface
“You would compress things with the harpoon, but this may not be enough to form a good anchor point,” he said.
“For a future lander, I believe a low indecent velocity will be the main requirement, so try for an even softer landing. That, and paint the lander a weird colour that isn’t the same as the surface of the comet in case it goes for a little jaunt again.”
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 November 12 that year, 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 at Abydos, 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.
“Philae had left us with one final mystery waiting to be solved. 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 underneath, which would give us invaluable access to billions-of-years’-old ice.”
With a team of mission scientists and engineers, he pulled together data from the instrument on board both the Rosetta orbiter and Philae to find out the location of the missing touchdown site.
A bright patch of sliced ice was spotted by a camera on the orbiter, and the site was confirmed by measurements made by the boom arm on Philae when it struck the surface.
A re-analysis 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 10 inches into the ice on the side of a crevice, leaving identifiable marks of its drill tower and sides.
Pictures and imaging taken from the Rosetta spacecraft showed shining bright spots where the lander had sliced away the surface, revealing water-ice covering an area of about 37 square feet (3.5 square metres.)
“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, or on top of waves at the seashore,” added Mr O’Rourke.
The team believes the site represents the overall state of the comet’s interior when it formed some 4.5 billion years ago. The new research was published in the journal Nature.