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Comet 67P/Churyumov-Gerasimenko is the main target of ESA's Rosetta missionand will be encountered in May 2014. As the spacecraft shall be in orbit thecomet nucleus before and after release of the lander {\it Philae}, it isnecessary necessary to know the conditions in the coma. Study the dustenvironment, including the dust production rate and its variations along itspreperihelion orbit. The comet was observed during its approach to the Sun onfour epochs between early-June 2008 and mid-January 2009, over a large range ofheliocentric distances that will be covered by the mission in 2014. Ananomalous enhancement of the coma dust density was measured towards the cometnucleus. The scalelength of this enhancement increased with decreasingheliocentric distance of the comet. This is interpreted as a result of anunusually slow expansion of the dust coma. Assuming a spherical symmetric coma,the average amount of dust as well as its ejection velocity have been derived.The latter increases exponentially with decreasing heliocentric distance (\rh),ranging from about 1 m/s at 3 AU to about 25-35 m/s at 1.4 AU. Based on theseresults we describe the dust environment at those nucleocentric distances atwhich the spacecraft will presumably be in orbit.  Astronomy and Astrophysics, in press

Evolution of the Dust Coma in Comet 67P/Churyumov-Gerasimenko Before 2009 Perihelion