Just as the Rio Olympics finish, the European Space Agency find their long-lost celestial triple jump champion, the Philae space probe. The washing-machine-sized Philae captured the world’s attention on 12 November 2014, when it landed on comet Churyumov-Gerasimenko.
No one – myself included – who was at the European Space Operations Centre (ESOC) in Darmstadt, Germany, for the landing could forget the sweep of emotions that this little robotic envoy generated. Partly because not everything went according to plan. But the hiccups only endeared the lander to the general public at large.
Although it touched down exactly where it was supposed to at exactly the right time, butter fingers Philae failed to anchor itself to the icy comet and so bounced across the surface for the next two hours before coming to rest in an unknown location.
The next day, Philae took some selfies that showed it was in a dark spot, wedged on its side in some kind of crevice with one leg sticking up into the sky. No one knew where this was but one thing was clear – there was not going to be much power falling on its solar panels. Once its primary battery drained, Philae would go silent.
For the next three days, as the power ebbed away from its electronic body, Philae worked hard and communicated with the Rosetta mothership, relaying data from its instruments. Meanwhile, back on Earth, engineers tried to figure out where the lander had come to rest.
Cartoons of the mission released by ESA transformed the spacecraft into a cute animation and prepared the world for the impending loss of power by showing Philae unrolling a sleeping bag to take a nap. Some first-person tweeting from the official Philae twitter account, @Philae2014, also provided a sense of personal connection to the plucky little robot.
The mission came to an end at 00:36 GMT on Saturday 15 November. Operators tweeted on behalf of the spacecraft, “I’m feeling a bit tired, did you get all my data? I might take a nap …”
The answer was yes, but although the data had flowed in and most of the mission’s objectives were met despite the strange angle of the lander, there were some analyses that proved impossible to complete without a knowledge of the lander’s location.
One of these was the CONSERT experiment, which beamed radar through the comet’s interior between Philae and Rosetta. This data could reveal the comet’s interior structure and composition but without knowing Philae’s location, the analysis could not be completed because the radar’s path through the comet was unknown. Now the final piece of this puzzle is in place and scientists can work towards understanding what lies inside the comet.
Comets are incredibly important in understanding how life began on Earth. They are deep-frozen time capsules from the formation of our planet 4.6 billion years ago, and preserve a record of the organic molecules that populated the early Earth and gave rise to life here. This was a major part of Philae’s mission: to build an inventory of these molecules.
It was said at the time that Philae was Europe’s “Apollo moment”. Sure it was a robot on a comet rather than humans on the Moon, but the sentiment was accurate. It was a stunning achievement that required the cooperation of thousands of people from many different countries, and woke the world up to the fact that great space achievements are no longer the sole preserve of the US and Russia. The only tiny blot on this achievement was failing to find Philae. Now, we have.
The identification of Philae is a resounding triumph for the European Space Agency. It means that every ounce of science can be wrung from those three days of data.
The confirming image was taken on 2 September. After months and years of looking at false alarms, Rosetta flew over Philae’s powerless shell at an altitude of 2.7km.
Characteristically for a mission that has been high on drama, the identification has been made just weeks before the mission is due to end by landing the Rosetta spacecraft itself on the comet – something it was never designed to do. But then, that’s what this mission has always been about.
During the celebration on the night of the landing in 2014, I was talking to Roger Bonnet, the former director of science at ESA who greenlit the Rosetta mission back in the 1980s. I had been at a press briefing all that time ago and heard Bonnet say with tongue in cheek that NASA had so much money that they did every mission possible. He quipped that this meant the only missions left for ESA to do were the impossible ones. That night in November 2014, I told him I now believed that he hadn’t been joking after all.
Stuart Clark is the author of The Search for Earth’s Twin (Quercus), and co-host of the podcast The Stuniverse (Bingo Productions).