From the europeanspaceagency on Flickr:
Rosetta is en route to Comet 67P/Churyumov-Gerasimenko, where it will make the most detailed study of a comet ever attempted. It will follow the comet on its journey through the inner Solar System, measuring the increase in activity as the icy surface is warmed up by the Sun. The lander will focus on the composition and structure of the comet nucleus material. It will also drill more than 20cm into the subsurface to collect samples for inspection by the lander’s onboard laboratory.