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Rosetta probe lander Philae on the surface of comet 67P/Churyumov-Gerasmineko, computer artwork. Gas and dust are evaporating from the comet's nucleus (core) to form the coma (thin atmosphere) and tail. The surface is depicted as rocky and solid but it may be a looser aggregation of ice and rock. The Rosetta mission of the European Space Agency (ESA) is scheduled to launch in February 2004, but will not rendezvous with the comet until 2018. It will be the first ever attempt at a cometary landing. The Philae lander will study the structure and chemical composition of the comet while the main spacecraft stays in orbit to relay communications back to Earth. (KEYSTONE/SCIENCE PHOTO LIBRARY/MARK GARLICK)