Contribution of Mars Odyssey GRS at Central Elysium Planitia

The neutron signals measured by the Neutron Spectrometer on board the Mars Odyssey satellite are analyzed at Central Elysium Planitia. The neutron currents have variations associated with the boundaries of geological units in all three energy ranges: thermal, epithermal and fast neutron. Geochemical constraints can be derived from the neutron data using macroscopic absorption cross sections. This variable measures the ability of a material to absorb neutrons, giving clues of its chemical composition. The neutron derived chemical constraints are compared with the elemental abundances measured by the Gamma Subsystem, also on board Mars Odyssey. Differences between the two datasets are interpreted to reflect heterogeneities of probed surfaces. The knowledge already derived from other observations and a detailed examination of the GRS datasets are used to determine a general overview of the geology of the region and possible mechanisms of emplacement. The particular role played by chlorine in this scheme is emphasized.