Engineers at the European Space Agency fear that they won't be able to communicate with the Philae lander after Friday. Here, lander manager Stefan Ulamec (left, in foreground) watches as data confirming the comet landing arrived Wednesday. European Space Agency hide caption

itoggle caption European Space Agency

The Philae lander beamed back images showing one of its three feet on the surface of Comet 67P/Churyumov-Gerasimenko . This photo is compiled from two images; a wider version will be released later Thursday. ESA/Rosetta/Philae/CIVA hide caption

itoggle caption ESA/Rosetta/Philae/CIVA

Closeup of Philae's primary landing Site J, which is located on the "head" of Comet 67P/Churyumov–Gerasimenko. The image was taken by Rosetta's OSIRIS narrow-angle camera on Aug. 20. ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA hide caption

itoggle caption ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

An illustration of what the Philae lander will look like at work on Comet 67P/Churyumov-Gerasimenko. AOES Medialab/ESA hide caption

itoggle caption AOES Medialab/ESA