PARIS (AFP) - Robot lab Philae drilled into its host comet on Friday with just hours of battery left, but may lose power before it can transmit results of a much-anticipated attempt to probe below the surface, mission scientists said.
Charged with 60 hours of onboard power, the lander bounced twice after initial touchdown Wednesday, settling at an angle in a crevice in an unknown location, shadowed from sunlight that could potentially have extended its battery life.
With its energy supply fast winding down, lander manager Stephan Ulamec said the drill was "started" on Friday, but contact between Philae and its orbiting mothership Rosetta was lost soon thereafter.
There are two communications windows per day - the next is due to open 2100 GMT (5am Singapore time) - by when Philae may have entered hibernation.
"Maybe the battery will be empty before we get contact again" to upload the data, which Philae transmits to Earth via Rosetta, said Ulamec, who urged onlookers to "cross your fingers".
"If we don't receive any data it's probably because the battery is flat."
It was not certain the drill had actually pierced the surface of comet 67P/Churyumov-Gerasimenko, which is racing towards the Sun at 18km per second.
Samples from its drill, one of 10 onboard experiments, had been among the most highly anticipated results from Philae's mission, with scientists hoping for clues to the formation of the Solar System and even the appearance of life on Earth.
But mission controllers underlined the exploration has already been a massive success, saying Philae's rough start has not stopped it from experimenting more or less as planned and relaying valuable data to Earth.
Washing machine-sized Philae landed on the comet after a nail-biting seven-hour, 20km descent from its orbiting mothership Rosetta, which had travelled more than a decade and 6.5 billion kilometres to get there.
The touchdown on the low-gravity comet did not go entirely according to plan, when Philae's duo of anchoring harpoons failed to deploy and it lifted off again... twice.
Ground controllers had by Friday not yet pinpointed Philae's position on the comet currently 510 million kilometres from Earth.
Besides 60 hours of power on its main battery, Philae was also designed with solar panels to recharge and extend the mission duration by as much as possible.
But in the lander's dark location, evident from photos and data it sent home, one solar panel was only receiving about 80 minutes of sunlight per 12.4-hour comet day and two others 20 or 30 minutes - much less than the six or seven hours engineers had bargained on.
When it eventually does fall into slumber, there is always the off chance that Philae may be jolted back to life months in the future as comet "67P" draws closer to the Sun, they added, and may then pass on outstanding data.
But, "we would have to be extremely lucky," said mission scientist Valentina Lommatsch.
So far, the 100kg laboratory has sent back the first-ever photos taken from a comet surface, and has probed the ancient Solar System traveller's surface density, temperature and composition.
Even without drilling, "we should harvest at least 70 to 80 per cent of the scientific data we had expected from Philae's first (60-hour) phase," astrophysicist Philippe Gaudon, who heads the Rosetta mission at French space agency CNES, told AFP.
The €1.3 billion (S$2.1 billion) 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 around 4.6 billion years ago.
Some scientists theorise that they may even have "seeded" Earth with some of the ingredients for life.
Rosetta, with Philae riding piggyback, 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.
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.