Rosetta finds the lost Philae lander as its own mission clock winds down

Just over two years ago, the Rosetta space probe successfully entered orbit around comet 67P/Churyumov–Gerasimenko (hereafter abbreviated as 67P). Rosetta’s mission has been a tremendous success — it’s the first probe to orbit a cometary nucleus and the first to accompany a comet as it traveled towards the sun. One notable failure early in the mission limited the information we could gather from 67P, however. The Philae lander, which launched on November 12 2014, failed to land in its target location. Now, with the Rosetta mission drawing to a close, the satellite “mothership” finally spied its errant daughter lodged in a crevice.

Philae’s problems began before it deployed, when administrators noticed a problem with its cold-gas thruster. That thruster was meant to reduce Philae’s bounce when it struck the surface of the comet, but it never fired. Instead, Philae struck the comet and bounced at least twice. The first bounce is believed to have moved it at roughly 15 inches per second — and while this sounds like a downright leisurely pace, an escape velocity of 17 inches per second would have been sufficient to launch Philae off into space, never to be seen again. (A video of the recreated landing can be seen here.)

Philae’s solar panels were unable to provide sufficient power for the craft to recharge, which left it dependent on batteries. Intermittent contact was established from June 13 – July 9 2015, and the lander managed to transmit some measurements it took with its CONSERT (COmet Nucleus Sounding Experiment by Radiowave Transmission) test device. After further communication proved impossible, the radio equipment Rosetta used to communicate with Philae was disabled to save power.

Now, with its own mission expected to end in a month, Rosetta has finally imaged Philae’s final resting place, as shown below:

Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The probe, as theorized, is resting on its side in a crevice, trapped in a shadowy niche that never gave it enough sunlight to perform its work. With available power dimming as 67P moves away from the sun, Rosetta is only expected to remain online for another month. Rosetta is currently set to descend and crash into 67P on September 30, using its last energy reserves to perform close-in analysis and detailed studies of the surface of the comet.

Annoted lander close-up. Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Rosetta’s time around 67P taught us that the comet had smaller-than-expected reserves of surface water ice and that the ratio of heavy water (deuterium-enriched) to normal water is significantly different than that of Earth. It also captured the outburst process, including confirming the presence of molecular oxygen. The mission also informed our understanding of early solar system formation — the lack of a magnetic field around 67P could mean earlier theories about how planets formed were incorrect or at least incomplete.