It’s getting colder by the day on the nucleus of comet 67P/Churyumov-Gerasimenko, currently some 300 million km from the Sun. Very soon now, the temperature and level of solar energy will be too low for Philae to function, that is if it’s still in an operable condition. The lander has not contacted the orbiter since 9 July last year. Something seemed to have stirred on 21 December, but unfortunately it proved only a false alarm. “We have no way of knowing whether Philae is receiving our commands and if it’s executing them but can’t transmit, or whether it has simply died,” explains Philippe Gaudon, Rosetta project leader at CNES.
No way of establishing Philae’s status
On 10 January, mission managers decided to ‘go for broke’ and send a command to spin the reaction wheel that was used to stabilize Philae during its descent to the comet on 12 November 2014 and shut down automatically once it touched the surface. Their idea was that spinning the wheel might move Philae or at least shake off the dust and other materials that have likely settled on it over time. Contact has not been restored since this manoeuvre, so it’s impossible to establish Philae’s status. There could be many reasons for this.
“Philae may no longer be able to receive our commands. It may not be generating enough power from its solar panels or its electronic circuitry or receivers may be inoperable.”
“Philae might also have received our commands and moved, but is incapable of telling us because its transmitters may no longer be working or there’s not enough power, as transmission requires 10 W more power than reception. Lastly, as any movement generated by spinning the reaction wheel was uncontrollable,
the lander could have ended up in an even worse position than before!
Philae’s status therefore remains shrouded in mystery and the chances of restoring contact with it are fading by the day. The orbiter is currently about 80 km from the comet’s nucleus and will be closing in over the months ahead. “According to the end-of-mission schedule, we expect the orbiter to come within less than 10 km of the nucleus in August,” says Philippe Gaudon. “At that point we hope to get a close look at Philae and its immediate environment (at a resolution of 10 cm). With hindsight, we will then be able to much better understand what happened and what it’s been doing, since everything we’ve assumed for months now—shadows from the relief around the lander, its attitude, the orientation of its antennas and so on—is based on calculations involving a certain margin of error.”
Philae is thought to be lying on its side on the surface of comet 67P. Credits: CNES/D. Ducros.
This picture of the surface of comet 67P was taken by the Rosetta orbiter on Christmas Day, 25 December 2015. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.