11/18/2014 10:47 EST | Updated 01/18/2015 05:59 EST

Philae lander drilling results reveal Comet 67P surface is hard ice

An experiment to drill into the surface of a comet for the first time has shown it is too hard to drill.

The Philae lander, the first spacecraft ever to land on a comet, used its MUPUS probe to hammer into the surface of Comet 67P/Churyumov-Gerasimenko "but was unable to make more than a few millimetres of progress even at the highest power level of the hammer motor," the European Space Agency (ESA) reported Tuesday on its blog for the Rosetta mission, of which Philae is a part.

Data from Philae suggest the comet’s surface is covered in a layer of dust 10 to 20 centimetres thick, on top of strong ice, or ice and dust mixtures, the Rosetta team says.

"If we compare the data with laboratory measurements, we think that the probe encountered a hard surface with strength comparable to that of solid ice," said Tilman Spohn, principal investigator for MUPUS, on the blog.

ESA said data from the Rosetta spacecraft that is orbiting the comet shows that overall the solid part of the comet – its nucleus – has a low density. That suggests the inside of the comet is more porous.

The MUPUS probe also contains instruments designed to measure temperature and acceleration. Some of the data could not be gathered because it was in Philae's harpoons, which didn't fire properly. But the probe did measure temperatures of -153 and 163 C after landing.

Philae made its historic landing on the comet on Nov. 12, and managed to send a load of data 500 million kilometres back to Earth before running out of battery power and shutting down for now. The lander is expected to wake up again in the spring of 2015, as the comet orbits closer to the sun, allowing more sunlight to hit Philae's solar panels. At that point, its instruments, including MUPUS, may be able to collect more data. 

In the meantime, the Rosetta spacecraft, which deployed Philae, continues to orbit the comet and collect data.