Philae Gathers Data Despite Rough Landing

Europe’s Philae robotic probe touched down on the dusty surface of Comet 67P/Churyumov–Gerasimenko on Nov. 12, marking a historic achievement in planetary exploration.

After a decade-long journey through space to rendezvous with 67P, the Rosetta mission has already racked up a slate of firsts in the fields of flight dynamics and cometary science. Led by the European Space Agency (ESA), the landing of a 100-kg (220-lb.) probe marks the crowning achievement in an already stunning exploration campaign.

But after a hardware malfunction left Philae without an active descent system, the lander's harpoon anchors failed to deploy and secure it to the comet's surface, and it appears to have bounced twice as it alighted.

As a result, Philae is likely stuck in an unstable position on uneven terrain in an area poorly illuminated and about 1 km from its original landing site, according to French space agency CNES.

"This is a new site, one we would not have analyzed as a possibility,” Marc Pircher, head of CNES Toulouse Space Center, said during a Nov. 13 news briefing.

CNES said in its current position, Philae is receiving only 90 minutes of sun exposure every 12 hours.

However, the probe is "alive and functioning," its antennas are pointed toward Rosetta, and it is relaying so-called "housekeeping" and science data from eight of its 10 instruments via the Rosetta orbiter.

The remaining two instruments -- APXS (Alpha X-ray Spectrometer) and part of MUPUS (Multi-Purpose Sensors for Surface and Subsurface Science) -- have not been activated in order to save power and avoid the possibility of causing further lander movement.

Yesterday, during pre-deployment checks, Philae mission managers said a hardware malfunction discovered hours before the lander's separation from Rosetta left the probe without an active descent system as it touched down on the comet.

As the probe reached the surface, its landing gear was to have absorbed the force of the touchdown while drills in the lander's feet bore into the comet’s surface and two harpoons locked the lander to the ashy terrain. At the same time, a thruster atop the lander was supposed to push it down, counteracting the impulse of the harpoons and drills in the opposite direction.

Less than an hour after touchdown, however, DLR confirmed that the cold-gas thruster designed to counter the lander’s impact failed to ignite.

CNES said its possible the harpoons deployed but were unable to anchor themselves into the comet's terrain without the impulse from Philae's cold-gas thruster system. While mission managers are considering firing the harpoons to secure Philae in its current location, the lander's pyrotechnics are now 10 years old, and it is uncertain how effective they would be in affixing Philae to its new landing site.