MicrOmega: An IR Hyperspectral Microscope for the Phobos Grunt Lander

Introduction: The coupling between imaging and spectrometry has proved to be one of the most promi sing way to study remotely planetary objects [1][2]. The next step is to use this concept for in situ analyses. MicrOmega IR has been developed within this scope in the framework of the Exomars mission (Pasteur paylaod). A demonstrator will be embarked on the Phobo s Grunt mission. It is an ultra miniaturized near-inf rared hyperspectral microscope dedicated to in situ analyses, with the goal to characterize the composition of Ph obos soil at almost its grain size scale, in a non destr uctive way. It will provide unique clues to trace back the history of Phobos, and will possibly contribute optimi zing the selection of the samples to return to Earth. Phobos origin: The origin of Phobos remains controversial. Its composition truly differs from that of Mars and appears like that of a primitive body [2]. This similarity led to the assumption that Phobos could be an asteroid captured by Mars. However, calculations seem to prove that this expectation is rather unlik ely [3]. Phobos could also result from an impact on Mar s, that could have led to the accretion of small marti an satellites, with Phobos and Deimos the latest remna nts, accreted close to the co-rotational orbit. The simi larity with primitive bodies would come from the lack of sufficient energy to enable a further differentiati on to take place. Other scenarios for Phobos formation an d evolution are still considered. MicrOmega should greaty contribute deciphering Phobos origin. Since surface samples should be repr esentative of the bulk of Phobos [4], the presence ( or not) of mafic minerals, altered products and carbon compounds in the samples will provide important clu es to answer these questions. Instrument concept: MicrOmega acquires reflectance spectra of 5 mm-sized samples with a spatial sampling of 20 μm. A monochromator, based on an AOTF (Acousto Optical Tuneable Filter), illuminates sequentially the sample in up to 500 contiguous wav elength channels (spectral sampling of ~ 20 cm ) covering the spectral range of interest (0.9 3.2 μm). For each channel, an image is acquired on a 2D detector , building a tridimensional (x,y, λ) image cube.