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Race to gather comet data before Philae's power dies

Paul Sutherland, Feature writer
Nov 14, 2014, 0:40 UTC, Updated Nov 14, 2014, 2:13 UTC

Sen—Mission Control, Darmstadt, Germany—European space scientists admitted today that they may have only a short time to gather data from their Rosetta probe Philae after it landed awkwardly on the surface of Comet 67P/Churyumov-Gerasimenko.

Philae’s harpoons failed to fire to secure it to the comet. So after touching down on the intended, flattish site called Agilkia, it bounced back into space for two hours before bouncing again to rest against a cliff.

The European Space Agency’s Rosetta orbiter is scouring the comet to see exactly where its companion craft is. But it is thought it could be lodged by a crater wall that is blocking sunlight from charging its batteries.

Philae appears to be leaning at a slight angle with just two of its three feet firmly on the surface, an afternoon press conference at ESA’s operations centre in Darmstadt, Germany heard today. And its solar panels are only getting one and a half hours of sunlight every 12 hours instead of the six or seven hours that was hoped for.

Philae’s lead scientist Professor Jean-Pierre Bibring said: “There is a huge cliff ahead of us and we are in the shadow of the cliff. That is part of the problem.” 

Earlier fears that the probe suffered damage when it bounced twice to a final stop were unfounded, and had been a “wild guess”, lander manager Dr Stephan Ulamec said. 

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An image taken by Philae's ROLIS imager when it was about 40 metres above the surface of Comet 67P/Churyumov-Gerasimenko. The dust-covered rock to upper right is about five metres wide. Image credit: ESA/Rosetta/Philae/ROLIS/DLR

The probe was communicating and engineers decided the solar panels were in good order and simply not getting the sunlight. He said they might try to change their orientation to see if this could be improved.

Dr Ulamec admitted: “We’re still not sure where we are. We know that the first jump lasted for two hours and the craft lifted up to one kilometre off the ground and probably a similar distance across the surface. Then there was another smaller jump that lasted for seven minutes.”

He said it was a mystery why the probe’s harpoons failed to fire to anchor itself safely to the comet, because the probe acknowledged that the command had been received.

Philae’s landing gear was designed to allow it to hop on the comet’s surface if it had to. Dr Ulamec said: “We need another jump. But in the position it is in now, we would not dare to operate that until we knew what it would mean.”

The lander part of the Rosetta mission had enough power on board to operate for around two and a half days. After that is must rely on a second battery that has to be charged by sunlight.

The unexpected landing means that the scientists have decided, for the moment, not to operate the lander's Sample and Distribution Device—a drill that was meant to cut more than 20cm (8in) deep into the comet’s surface.

They want to analyse the interior because it contains pristine material that is virtually unchanged from the birth of the Solar System 4.6 billion years ago.

Professor Bibring said they might be able to use the drill tomorrow night when they have done as much other science as they can before power is lost.

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A newly released and enhanced image of Philae pictured by Rosetta as it headed towards a landing on the comet. Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Another experiment to extend a little arm to taste the surface, called the Multi-Purpose Sensor for Surface and Subsurface Science (Mupus), has also been put on hold in case it destabilises Philae. But engineers say it could later be used to push the probe upright depending how they find it is oriented.

Another ray of hope is that when Philae’s power dies, it will go into hibernation mode and so might be woken again later if its landing site begins to receive more sunlight in the weeks or months ahead.

Despite the snags, the exhausted mission team are thrilled with what has already been achieved. The other eight of Philae’s ten experiments are all working well and returning data. And the Rosetta mothership will continue to orbit and study the comet until late 2015 at least.

Professor Bibring said the mission was a story of success rather than failure. He said: “It is gorgeous where we are.”