Before they can say for certain if they'll be able to restore contact with Philae, scientists first need to find out where on the 4-kilometre-wide comet the washing machine-sized lander is, he added.
New pictures released Monday offer very good clues about where it has come to rest.
The high-resolution images taken from Philae's mother ship Rosetta show the lander descending to the comet and again after its first and second bounce. These were caused by the lander's failure to deploy its downward thrusters and harpoons.
Scientists at the German Aerospace Center, DLR, said Monday that an initial review of data the lander sent back 500 million kilometres to Earth showed the comet's surface is much tougher than previously assumed. There's also evidence of large amounts of ice beneath the lander.
Scientists are still waiting to find out whether Philae managed to drill into the comet and extract a sample for analysis.
Material beneath the surface of the comet has remained almost unchanged for 4.5 billion years, so the samples would be a cosmic time capsule that scientists are eager to study.
One of the things they are most excited about is the possibility that the mission might help confirm that comets brought the building blocks of life -- including water -- to Earth.
See more here: rosetta.esa.int
-AP