Telemicroscopy and close-up imaging for the Rosetta Landers

Abstract

Microscopic imaging allows to study the fine-scale texture and morphology of the cometary surface. The analysis supplements the surface mapping by the orbital Narrow Angle Camera at the landing site of the Rosetta lander systems. The microstructure of the cometary surface is almost unknown and of high interest. The texture influences several physical properties of the comet like surface temperature, heat and gas flow through the surface, density of the surface layer, thermal diffusion and activity behavior. From theoretical models about the origin of comets and from GIOTTO measurements one can expect dust grains containing organic components in the micron to millimeter range. These particles can becemented and form a coherent crust. Although it will be less likely to see exposed ice deposits at the non-active surface, the presence of ice grains cannot be excluded. Also, low density dust deposits coud be present. For this reason, monitoring of the texture and small scale features with a spatial resolution better than 100 m is recommended. In addition to microscopic study, wide-field imaging of areas in the vicinity of the lander is necessary both for giving context to the close-up measurements and for supporting other experiments. For this reason a certain panorama imaging capability is also recommended. We propose for the Rosetta lander systems a camera concept which allows to obtain images of the surface with high spatil resolution (better than 50 m/pix) and a moderate field of view at infinity. Spectral capabilities can be achieved by means of spectral filters in the VIS-NIR range. As possible alternatives, a stand-alone telemicroscope and a stand-alone panorama camera will be discussed.