After months of searching, the Euopean Space Agency (ESA) has given up the hunt for the lost Philae comet lander. Despite having narrowed the final resting place of the unmanned probe to a "landing strip" measuring 350 x 30 m (1,150 x 100 ft) on comet 67P/Churyumov-Gerasimenko, the space agency has been unable to locate it and has commanded the Rosetta spacecraft to move into a higher orbit as it continues its science mission.

The Philae lander was the first manmade object to attempt a soft landing on a comet. On November 12, 2014, the lander made contact with the surface of 67P, but due to a malfunction in its landing systems it was unable to anchor itself. As a result, it rebounded four times before finally coming to rest at an unlocated site called Abydos.

Unfortunately, the spacecraft landed on its side next to a crater or cliff wall, where not enough sunlight could reach its solar panels and provide power. After 60 hours, the batteries went dead and Philae went into hibernation.

Since then, ESA has been trying to locate Philae from images taken during the descent, and by sending Rosetta over the suspected landing area at an altitude of 18 to 28 km (11 to 17 mi). Each pass was timed to coincide with the 1.3 hours per comet revolution that the lander was illuminated. However, the timing was also when the area was marked by long shadows and though Rosetta's instruments did narrow down the search area, the exact final resting place of Philae remains a mystery.

Rosetta has now moved into a new orbit as it continues its mission. This is farther out and provides fewer opportunities for looking for Philae. At its current distance, the resolution is so low that the lander would appear as three dots – and on a surface strewn with craters and boulders that's very easy to lose in the background. Also, the mission schedule means that future searches will be opportunistic.

Lander search area (Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)

“Rosetta’s busy science schedule is planned several months in advance, so a dedicated Philae search campaign was not built into the plan for the close flyby,” says ESA’s Rosetta project scientist Matt Taylor. “We’ll be focusing on “co-riding” observations from now on, that is, we won’t be changing the trajectory of Rosetta to specifically fly over the predicted landing zone in a dedicated search, but we can modify the spacecraft pointing and/or command images to be taken of the region if we’re flying close to the region and the science operations timeline allows.”

ESA's main hope is that as 67P draws closer to the Sun enough light will reach Philae to generate enough power to send back a signal. However, this depends on exactly how much light the probe receives during each comet "day," the effects of the gas and dust jetting out of the comet as the Sun heats it, and the effect of the cold on the spacecraft's electronics during hibernation. The space agency points out it won't be until late March that the environment is warm enough to allow a reboot and it may be as late as June before the Sun is strong enough to generate the 17 Watts needed. However, engineers remain optimistic that if Philae can recover, it could be capable of resuming experiments as the comet approaches perihelion.

Source: ESA

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