The emission of large dust particles from comet 67P/Churyumov-Gerasimenko constrained by observation and modelling of its dust trail

The abundance and properties of dust particles larger than about 60 m emitted by comet 67P/Churyumov-Gerasimenko are constrained by evaluating astronomical images of its dust trail. Such particles carry the bulk of refractory mass released from comets to interplanetary space. In contrast to smaller particles, they remain on trajectories similar to that of the parent comet during many revolutions around the Sun. They are observable as a narrow structure along the projected comet orbit, the dust trail. The first observation evaluated in this thesis was carried out in April 2004 in visible light with the Wide Field Imager on the ESO/MPG 2.2m telescope on La Silla (Chile), when the comet was at a heliocentric distance of 4.7AU. Two observations were performed in August 2005 and April 2006 at mid-infrared wavelengths (24 m) with the MIPS instrument on board the Spitzer Space Telescope. In both instances, the comet was at 5.7AU from the Sun, having passed aphelion in November 2005. To interpret the data, simulated images of the cometary dust trail are generated. The adopted model of cometary dust emission has five free parameters: the exponent of the dust size distribution, the particle emission speeds, the radiation pressure efficiency, the dust albedo, and the dust production rates. For these parameters, values are derived that are most suitable to reproduce the observations. The results for the first four parameters are in agreement with expectations. But the derived production rates cannot be reconciled with the measured brightness of the coma in the inner solar system