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

TL;DR

This study analyzes the dust coma evolution of Comet 67P before perihelion, revealing a slow expansion and increased dust ejection velocity as the comet approaches the Sun, informing expectations for the Rosetta mission.

Contribution

It provides the first detailed measurements of dust production and ejection velocities of Comet 67P during its approach to the Sun, prior to the 2009 perihelion.

Findings

Dust ejection velocity increases exponentially with decreasing heliocentric distance.

Anomalous dust density enhancement observed near the nucleus.

Dust scalelengths grow as the comet approaches the Sun.

Abstract

Comet 67P/Churyumov-Gerasimenko is the main target of ESA's Rosetta mission and will be encountered in May 2014. As the spacecraft shall be in orbit the comet nucleus before and after release of the lander {\it Philae}, it is necessary necessary to know the conditions in the coma. Study the dust environment, including the dust production rate and its variations along its preperihelion orbit. The comet was observed during its approach to the Sun on four epochs between early-June 2008 and mid-January 2009, over a large range of heliocentric distances that will be covered by the mission in 2014. An anomalous enhancement of the coma dust density was measured towards the comet nucleus. The scalelength of this enhancement increased with decreasing heliocentric distance of the comet. This is interpreted as a result of an unusually 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 these results we describe the dust environment at those nucleocentric distances at which the spacecraft will presumably be in orbit. Astronomy and Astrophysics, in press