A Halloween Message from Philae

A Halloween Message from Philae

29/10/2020Written by Malika Andress

Philae’s second touchdown site discovered at ‘skull-top’ ridge

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Image Credit: ESA

Four years ago the Rosetta mission came crashing to an end with a controlled impact on comet 67P/Churyumov–Gerasimenko.

Ever since Rosetta’s initial arrival at the comet back in 2014 (surprise, it’s duck shaped!), this European Space Agency mission has been full of the unexpected.

Mission highlights include Philae’s bouncy landing (and subsequent sleep, reawakening, and recent rediscovery), the presence of organic molecules on the surface of comet 67P/C-G that could help explain how Earth got the essential building blocks of life, the surprising abundance of oxygen in the comet’s atmosphere, and the fact that we all got really excited about comets again.

Images: Touchdown 1: ESA/Rosetta/Philae/ROLIS/DLR; all other images: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Analysis: O’Rourke et al (2020)

The mission may have physically ended, but on 27 October 2020 the official Philae lander Twitter account tweeted:

There is something I would like to tell you…
tomorrow at 17:00 CET.

After years of detective work, the second touchdown site of Rosetta’s Philae lander has been located on Comet 67P/Churyumov-Gerasimenko in a site that resembles the shape of a skull. Philae left its imprint in billions-of-years-old ice, revealing that the comet’s icy interior is softer than cappuccino froth.

“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,” said 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.

Image Credit: ESA

Image Credit: ESA

Image Credit: ESA

Image Credit: ESA

On 12 November 2014, Philae touched down on the comet, but it bounced when its anchoring harpoons failed to deploy and a thruster designed to hold the probe to the surface did not fire. After bouncing off the surface twice, Philae achieved the first-ever “soft” (non-destructive) landing on a comet nucleus, although the lander’s final, uncontrolled touchdown left it in a non-optimal location and orientation.

Philae was designed to support Rosetta’s study of the comet. It was equipped with sensors that could measure the composition of the gases being ejected close to the comets surface. The landers drill discovered that sections of the comet were solid ice, this supported the theory that water on the Earth could have been brought here by comets during the formation of the solar system. Working in conjunction with Rosetta signals were beamed through the comet in an attempt to calculate the density of the comet, this would offer more insights into what it is made of.

On 15 November 2014 Philae entered safe mode, or hibernation, after its batteries ran down due to reduced sunlight and an off-nominal spacecraft orientation at the crash site.

On 13 June 2015, ground controllers received an 85-second transmission from Philae, forwarded by Rosetta, indicating that the lander was in good health and had sufficiently recharged its batteries to come out of safe mode. Philae sent historical data indicating that although it had been operating earlier than 13 June 2015, it had been unable to contact Rosetta before that date.