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Philae somewhere on comet - ESA

Paris - Robot probe Philae bounced twice after its historic comet landing, probably ending up with one leg dangling in space, in the shadow of a cliff that could prevent it fully charging its battery, ground control said on Thursday.

In the 24 hours since its pioneering deep-space contact, the lab has sent home a slew of data and photographs from the surface of comet 67P/Churyumov-Gerasimenko - though from a mystery location thought to be hundreds of metres off target.

Harpoons were meant to anchor Philae to the low-gravity comet 510 million kilometres (320 million miles) from Earth and zipping towards the Sun at 18 kilometres per second (11 miles per second).

The harpoons failed to deploy, but this has not prevented Philae sending information to Earth via its orbiting mothership, Rosetta.

"We have a better understanding of how we got there, but we still do not really know where," lander manager Stephan Ulamec said in a press conference webcast live from European Space Agency (ESA) ground control in Darmstadt, Germany.

"We could be somewhere in the rim of this crater," he added, pointing to a surface shot on which deep crevices lie in permanent, pitch-black shadows.

"We are not standing parallel to the surface," said Ulamec - an evaluation gleaned from the angle of photographs Philae has sent to Rosetta to be relayed to Earth.

Eight of the washing machine-sized Philae's 10 onboard science instruments and cameras have kicked into action as planned - a highlight achievement in the ESA's flagship €1.3bn ($1.6bn) project.

The data from some of these revealed that the first bounce, "a huge leap" according to Ulamec, lasted about two hours and moved the probe a kilometre (0.6 miles) from its target site, followed by a second, smaller rebound.

There are fears that Philae may not be able to use the drill with which it was equipped to take sub-surface comet samples for chemical testing.

"We are almost vertical - one foot probably in open space" and two on the comet surface, said mission scientist Jean-Pierre Bibring.

And Philippe Gaudon of France's CNES space agency earlier said the probe was "likely on a steep slope".

Trying to activate the drill, or even the harpoons, without knowing the lander's location and orientation could be dangerous.

"We may just tip over our lander," said Ulamec, adding Philae may not have enough power for "a dedicated jump out of the hole in which we may be."

The probe's battery will only last about 60 hours, and given its awkward position, Philae was not getting enough sunlight for a full recharge - receiving only 1.5 hours per day instead of the six or seven required.

Success

Wednesday's elation at the landing signal from Philae after a seven-hour descent, soon turned to worry as fluctuations in the radio signal indicated the 100-kilogramme lander may have lifted off again.

This was followed by a long silence until Thursday's briefing, where ESA experts underlined the mission's successes - including the first-ever pictures taken from the surface of a comet.

"Many of the... instruments have already acquired what they wanted to," said Bibring.

"What is really impressive is not the degree of failure, but the degree of success."

The Rosetta mission aims to unlock the secrets that comets, primordial clusters of ice and dust, are thought to hold about how the Solar System was formed about 4.6 billion years ago.

Some scientists theorise that comets may even have "seeded" Earth with some of the ingredients for life.

Rosetta, carrying Philae, was hoisted into space in 2004, and reached its target in August this year, having used the gravitational pull of Earth and Mars as slingshots to build up speed.

The pair covered 6.5 billion kilometres (four billion miles) together before Wednesday's separation and Philae's 20-kilometre descent.

Philae was designed to touch down at a gentle 3.5 km per hour, then fire two harpoons into a surface engineers hoped would provide sufficient grip to allow the robot to do its experiments.

The lander complements 11 instruments aboard orbiting Rosetta, a three-tonne orbiter responsible for four-fifths of the mission's expected science haul.

Whatever happens to Philae, Rosetta will continue to escort the comet as it loops around the Sun.

On August 13, 2015, they will come within 186 million kilometres of our star, before heading off to the outer Solar System.

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