We misplaced a robot on a comet and found it again two years later

  • September 07, 2016

Do you remember the Rosetta mission we covered back in 2014?

Here's a quick recap: The European Space Agency (ESA) launched a spacecraft in 2004 that was designed to chase down a comet and study it. Rosetta spent nearly 10 years just reaching the comet, named 67P/Churyumov-Gerasimenko. After years of hibernation, Rosetta "woke up" and started doing science in orbit around 67P in 2014.

But the mission went one step further. Hitching a ride with Rosetta was a small landing probe called Philae, and after a nail-biting manoeuvre that had never been tried before, it reached the surface of 67P on 12 Novermber 2014.

However, when one of Philae's harpoons failed to fire, the probe bounced off the surface of the almost gravityless comet and back into space, perhaps up to a kilometre.

After a few more bounces, scientists finally received a signal from Philae to say that it had touched down – humanity's first-ever comet landing was a success.

But there were more challenges. Nobody knew where Philae had eventually ended up, although the signal indicated that it wasn't getting enough sunlight on its solar panels, and was losing power fast.

This drastically reduced the time left to conduct experiments, and suddenly the race was on to complete as many tasks as possible while Philae could still send a signal.

Communication was lost on 15 November, but not before the Philae mission was considered a success:

"Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence ... This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered," German Aerospace Center's lander manager Stephan Ulamec was quoted as saying.

Through an engaging and innovative social media campaign, "little Philae" won over the hearts and minds of the public who followed the pioneering mission, and the robot's eventual demise was an emotional moment for the Earthlings back home whose dreams of discovery it represented.

Where's Wall-E?

We heard from Philae again briefly last year as the comet got closer to the sun and charged the lander's batteries, enough for it to briefly spark back into life and send a few final signals. But the team was never able to spot exactly where it had landed. They suspected it was in a rocky crevice, in a shadow, but the orbiting Rosetta probe wasn't able to spot it in any images.

That is, until this week:

Rosetta had to get right up close to comet 67P – less than three kilometres away – to get a glimpse of Philae's final resting place. With less than a month left of the mission, a final glimpse of the little lander is a fitting farewell to a mission that has helped humans understand more about the basic building blocks of the solar system.

Philae found! An image from Rosetta with the approximate location of Philae on the small lobe of comet Churyumov-Gerasimenko marked (Image: ESA/Rosetta/MPS for OSIRIS Team)

“This remarkable discovery comes at the end of a long, painstaking search,” said Patrick Martin, ESA’s Rosetta Mission manager. “We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour.”

“It’s a huge psychological bonus to finally know where it is,” agreed Rosetta project scientist Matt Taylor.

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