How to catch a comet [Space Comet Tracking]

IMAGINE THE excitement of sampling cosmic wanderers dating from before the birth of the Sun. Imagine, too, that these ancient relics are made not from rock or iron but from light volatile aggregates of ice and dust that, despite their delicacy, have survived for billions of years. On 6 July 2014, the European Space Agency´s (ESA) Rosetta probe entered orbit around just such a remarkable specimen, Comet 67P/Churyumov-Gerasimenko, a chunk of dust and ice shaped like an unshelled peanut 4km long.