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The Colour and Stereo Surface Imaging System (CaSSIS) is the main imaging system onboard the European Space Agency’s ExoMars Trace Gas Orbiter (TGO) which was launched on 14 March 2016. CaSSIS is intended to acquire moderately high resolution (4.6 m/pixel) targeted images of Mars at a rate of 10–20 images per day from a roughly\ud circular orbit 400 km above the surface. Each image can be acquired in up to four colours and stereo capability is foreseen by the use of a novel rotation mechanism. A typical product from one image acquisition will be a 9.5 km×∼45 km swath in full colour and stereo in one over-flight of the target thereby reducing atmospheric influences inherent in stereo and colour products from previous high resolution imagers. This paper describes the instrument including several novel technical solutions required to achieve the scientific requirement

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[1] Iron core differentiation of terrestrial planetary bodies is thought to have occurred simultaneously with planetary accretion. The exact mechanisms of core formation, however, remain incompletely understood. One model proposes that cores are formed from numerous smaller iron cores from predifferentiated planetesimals. To further understand this mechanism for forming Mars-and Earth-sized bodies, we present here systematic numerical simulations. Our models include a non-Newtonian temperature-, pressure-and strain rate-dependent viscoplastic rheology. Four different core formation regimes are being observed in the study, as a function of activation volume, friction angle, Peierls stress, and the initial temperature state of the body. We derive scaling laws, which show the importance of shear heating localization and plastic yielding as mechanisms to drive planetary differentiation in planetary interiors, that are in good agreement with numerical simulations. Results indicate that the effective rheology of the planetary body has a major effect on the core formation mechanism: while bodies with a weak rheology generally show a diapiric mode of core formation, the interior of planetary bodies with a stiff rheology can be fractured or displaced toward the surface. On Earth-sized protoplanets, the water content seems also to have a significant influence on the mode of core formation. Results indicate a time scale of differentiation of a few million years, significantly shorter than expected from the Stokes sinking time in a Newtonian medium.