The Philae robot probe on comet 67P has sent another stream of data back to Earth before losing power.
Everything expected from the Philae lander was delivered, just before low battery power dropped it into standby mode.
The robot is shadowed by a cliff and cannot get enough light on to its solar panels to recharge its systems.
Engineers fear this contact may have been its last – certainly for a while.
A tweet from the official Philae lander account said: “I’ll tell you more about my new home, comet 67P soon… zzzzz.”
Philae descended to the comet’s surface on November 12 – the first time in history that a space mission has made a soft landing on a comet.
The next opportunity to talk to Philae will come at around 11:00 GMT on November 15, when the orbiting Rosetta satellite – which delivered it to the 4km-wide “ice mountain” – comes over the horizon.
With only 1.5 hours of sunshine falling on the robot during the comet’s 12-hour day, it seems doubtful the battery will have recovered enough performance to complete the radio link.
Engineers did manage to maximize the possibility of it happening, though, by sending a command to reorientate the lander.
This involved raising Philae by 4cm and rotating its main housing by 35%. This will ensure the largest solar panel catches the most light.
Even if the probe falls silent over the weekend, researchers say they are thrilled with the amount of data already acquired.
Stephan Ulamec, lander manager, said: “Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence.
“This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered.”
In the latest tranche of data are the results from the drilling attempt made earlier in the day.
This had been an eagerly anticipated activity. Getting into the surface layers and bringing up a sample to analyze onboard was seen as central to the core mission of Philae.
Controllers say Cosac, the Philae laboratory that was due to receive the sample, downlinked its data, but that its contents had yet to be assessed.
Among other returns, Philae took another picture of the surface with its downward-looking Rolis camera.
It also exercised its Consert instrument. This is an experiment that sees Philae and Rosetta send radiowaves through the comet to try to discern its internal structure.
It has the additional possibility of being used to help triangulate a precise position for Philae on the comet’s surface.
This is still unknown. Although the robot hit the centre of its intended landing zone on Wednesday, it then bounced twice before coming to a stop.
Knowledge of that final resting location would enable engineers better to understand its predicament and the prospects for future contact if lighting conditions somehow change on 67P.
This could happen as the comet moves through space on its journey around the Sun. It will have seasons, just as the Earth does, and this could play to Philae’s advantage by altering the angle, timing and intensity of the sunlight hitting the solar panels.
Philae was launched from Earth, piggybacked to the Rosetta satellite, in 2004.
The pair covered 6.4 billion km to reach Comet 67P out near the orbit of Jupiter.
Scientists hope the investigations at the rubber-duck-shaped ball of ice and dust can provide fresh insights on the origins of the Solar System.
Whatever happens to Philae, Rosetta will continue to make its remote observations of 67P.
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