Search for Traces of Chemically Bound Water in the Martian Surface Layer Based on HEND Measurements onboard the 2001 Mars Odyssey Spacecraft

Abstract

Analysis of the distribution of the epithermal and fast neutron fluxes from the Martian surface within the ±60° latitude zone measured by the High-Energy Neutron Detector (HEND) from mid-February through mid-June 2002 has revealed regional neutron-flux variations outside the zones of climatic effects, which appear to be attributable to the presence of chemically bound water. With the exception of the epithermal neutron fluxes in Arabia and southwest of Olympus Mons (Medusae Fossae), these variations show no correlation with the geologic structure of the terrain at the level of global geologic maps. The lack of such a correlation probably implies that to the formation depth of the epithermal neutron flux (1–2 m), let alone the fast neutron flux (20–30 cm), much of Mars is covered by a surface material that bears little relation in composition to local bedrocks. Clearly, this is an aeolian cover whose fine-grain component was mixed by dust storms in the geologic time on the scale of large regions. The decrease in the flux of epithermal neutrons in Arabia and southwest of Olympus Mons (Medusae Fossae) appears to be attributable to an enhanced concentration of materials containing chemically bound water (clay minerals, palagonite, hydroxides, and hydrosalts) in the surface layers of these regions.