The Stereo Imaging Channel of SIMBIOSYS for the BepiColombo ESA mission

BepiColombo is the fifth Cornerstone mission of the European Space Agency (ESA) foreseen to be launched in August 2014 with the aim of studying in great detail Mercury, the innermost planet of the Solar System. Mercury is very important from the point of view of testing and constraining the dynamical and compositional theories of planetary system formation. In fact, being in close proximity to the Sun, it has been subjected to the most extreme environmental conditions, such as high temperature and large diurnal variation, rotational state changes due to Sun induced tidal deformation, surface alteration during the cooling phase, and chemical surface composition modification by bombardment in early history. Mercury has been studied by the Mariner 10 spacecraft in 1974-75 [1], when less than half of the planetary surface has been imaged at low resolution (scale factor from few hundreds of meters to 1-2 km/px) and its magnetic field and exosphere have been discovered. Since then, the only other satellite reaching Mercury is the NASA MESSENGER, that has very recently realized three flybys with the planet; MESSENGER will be inserted in orbit around Mercury in March 2011. The BepiColombo payload will consist of two modules: the Mercury Planet Orbiter (MPO), realized in Europe, carrying remote sensing and radio science experiments, and the Mercury Magnetospheric Orbiter (MMO), realized by JAXA in Japan, carrying field and particle science instrumentation. These two complementary packages will allow to map the entire surface of the planet, to study the geological evolution of the body and its inner structure, i.e. the main MPO tasks, and to study the magnetosphere and its relation with the surface, the exosphere and the interplanetary medium, i.e. MMO targets. The imaging and spectroscopic capability of the MPO modulus will be exploited by the Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIOSYS), an integrated system for imaging and spectroscopic investigation of the Mercury surface [2]. SIMBIOSYS incorporates capabilities to perform 50-110 m spatial resolution global mapping in both stereo mode and color imaging, high spatial resolution imaging (5 m/px scale factor at periherm) in panchromatic and broad-band filters, and imaging spectroscopy in the 400 - 2200 nm spectral range. This global performance is reached using three channels: the STereoscopic imaging Channel, STC [3]; the High Resolution Imaging Channel, HRIC [4]; and the Visible and near-Infrared Hyperspectral Imager, VIHI. STC main scientific objective is the global stereo mapping of the entire surface of Mercury that will permit the generation of a Digital Terrain Model (DTM) of Mercury's surface, improving the interpretation of morphological features at different scales and clarifying the stratigraphic relationships between different geological units.