The European Space Agency says it hasn’t received data from the lander since July 9.
Philae’s project manager, Stephan Ulamec, said the pattern of sunlight on the lander’s solar panels appears to have changed, possibly due to a slight shift in position triggered by gas coming out of the comet.
One of Philae’s two transmission units also appears to be faulty.
Scientists plan to send further commands to the lander and hope it responds again, as has happened before.
The mission will now focus on the spacecraft Rosetta, which is following comet 67P/Churyumov-Gerasimenko that Philae is on as it goes around the sun.