An analysis of new data from the final descent of the EU’s Philae comet lander suggests that the craft grazed the edge of a crater after its initial bounce on the comet’s surface, losing orientation and beginning to tumble before somewhat miraculously landing upright.

EU's Philae Comet Lander Grazed Crater During Landing

New data indicates unknown impact during Philae’s landing

It was reported on Tuesday that magnetic field data acquired by the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP) instrument suggests that it is likely that one of the lander’s legs scraped against something on the comet (perhaps a crater rim) following its initial bounce on the comet surface. This slight contact in the near-weightless environment on the comet both slowed down Philae’s descent spin rate and sent it tumbling as it bounced away from its original landing site

Background on the Philae comet lander mission

The Philae comet lander arrived at comet 67P/C-G after riding piggyback aboard the EU’s Rosetta spacecraft through for over ten and a half years. The more than 100 kg Philae craft was deployed from the orbiting Rosetta on November 12th, taking almost seven hours to reach the surface of the comet. Although the landing appeared to be successful based on initial telemetry, mission control soon discovered that the lander did not come to a smooth landing and secure itself to the comet as planned, but instead bounced a number of times past the planned landing zone and ended up in an unknown shadowy location.

Even though Philae is currently in hibernation mode due to its shadowed location, it’s quite possible that it will get sufficient sunlight to recharge its batteries and come back to life as the comet gets closer to the sun during the first half of 2015. In an interesting twist of fate, its current shaded position means the lander will avoid overheating during perihelion, very likely extending Philae’s overall operating lifetime.

Statement from EU mission control

“It was not a touchdown like the first one, because there was no signature of a vertical deceleration due to a slight dipping of our magnetometer boom as measured during the first and also the final touchdown,” explained  ROMAP co-principal investigator Hans-Ulrich Auster in a recent interview. “We think that Philae probably touched a surface with one leg only — perhaps grazing a crater rim — and after that the lander was tumbling. We did not see a simple rotation about the lander’s z-axis anymore, it was a much more complex motion with a strong signal in the magnetic field measurement.”

“It was really an exciting and almost unbelievable excursion,” Auster noted.