Optical Detection and Characterization of Cometary Grains Collected for Analysis by the COSIMA Mass Spectrometer on-board ROSETTA.

Abstract:

The COSIMA time of flight mass spectrometer on board the ROSETTA spacecraft (Kissel et al., 2007, 2009) will provide the first in-situ high resolution spectra of cometary grains. The first results on mass spectra will be presented in companion abstracts (e.g. Hilchenbach et al.). The grains are collected by three 10 mm x 10 mm targets exposed simultaneously in front of a funnel. The first exposed targets are covered by a very smooth “metal black” layer (gold and silver). Given the relatively low dust flux expected during the first stages of the RV phase and the non-renewable supply of Indium in the ion source, identifying the best candidate collected grains is a critical issue. For this purpose, COSIMA images the targets by presenting them before and after exposure in front of a camera (“COSISCOPE”), with grazing incidence illumination from opposite directions by two LED’s. The images will also provide information on the scattering properties of the collected grains. The resolution of the camera is 14 µm / pixel, which makes it possible to identify features filling up a significant fraction of the analyzed spot (50 µm FWHM).

 

The images of the first targets before and after exposure are downloaded without compression and with sub-pixel sampling for providing maximum resolution. Several algorithms have been developed so as to provide a priority ranking of features to be analyzed by SIMS. The results of this process will be presented, as well as the relationship between the optical signatures of high priority features and the outcome of the SIMS analyses.

 

References:

Kissel J. et al. (2007) Space Science Reviews, 128, p. 823-867

Kissel J. et al. (2009) in ROSETTA : ESA's Mission to the Origin of the Solar System, edited by R. Schultz and et al., pp. 201-242, Springer Science.

Hilchenbach M. et al. (2014) AGU fall meeting, 2014