Two harpoons were meant to anchor Philae to the frozen surface but both failed to fire, ESA said. Ice screws on its legs may also have failed to work.
The shade of the cliff face means that the solar panels, which should be recharging the lander's secondary batteries, are receiving only about 1.5 hours of sunlight compared with the scheduled six or seven hours of recharging time.
The primary batteries are expected to run out of power within the next two to three days as Philae had enough on-board battery power to last about 64 hours from the time of landing. Ground engineers are analysing whether it might be possible to adjust its solar panels, which are wrapped around the lander's body, to extend Philae's working life.
Almost all of Philae's instruments are working well and ESA scientists said that the Rosetta mission has already accumulated more data on a single comet than any previous space mission, despite the less-than-perfect landing.
"Philae is stable, sitting on the [comet's] nucleus and is producing data. The lander is very healthy," said Gerhard Schwehm, a scientist on the Rosetta mission.
However, the precarious landing means that a plan to drill into the comet may have to be postponed indefinitely because of the risk of destabilising the lander.
Rosetta is the first mission to orbit a comet and the first to land a robotic probe on its icy surface. It took 10 years since its launch in 2004 for Rosetta to travel to comet 67/P, which currently 510m km (311m miles) from Earth in the direction of the constellation Sagittarius.
"Do not have the impression this is a failure. What is really amazing is not the degree of failure but the degree of success. It's gorgeous where we are," said Professor Jean-Pierre Bibring, the lead landing scientist on Rosetta.
"We are just in the shadow of a cliff. We are in a shadow permanently, and that is part of the problem," Professor Bibring said from ESA's mission control in Darmstadt, Germany.
"We're almost vertical. One foot probably is in open space and two feet are on the surface. It could be that we are somewhere in the rim of this crater, which could explain this bizarre orientation," he said pointing to an image of the landing crater on the comet's smaller lobe.
"[Still] many of the other instruments have already acquired what they wanted to. A lot of science is getting covered now. We might try to better orientate the solar panels," he added.
If the solar panels were working at full throttle, the Philae lander could still be collecting and transmitting data through to next March, when the surface temperatures are expected to become too high for its instruments to function.
It may still be possible to perform some manoeuvres that could bounce the lander back into the sunlight, but ESA is unlikely to take this risk unless there is nothing to lose in terms of gathering further data.
It is also possible that as the comet moves closer to the Sun, and angle of sunlight might change, bringing Philae out of the shadow. If this happens, the batteries, which are designed to go into "hibernation", might start to recharge themselves and so trigger a second contact with the Rosetta mothership overhead.
But even if the Philae lander runs out of power within the next few days, the Rosetta spacecraft will continue to orbit the comet as it makes its closest approach to the Sun, sending back images and data for another 12 months, ESA said.
- The Independent
