The evidence for unusually high hydrogen abundances in the central part of Valles Marineris on Mars

Studies of hydrogen deposition in the shallow Martian subsurface have been conducted by two neutron and one gamma-ray detectors in the past and provided global hydrogen maps (Boynton et al., 2002; Feldman et al., 2002; Mitrofanov et al., 2002). It is known from these maps that hydrogen is most abundant in the polar permafrost areas compared to the equatorial band where frozen water is not stable on the surface. However, the spatial resolution of hundreds of kilometres typical for these maps does not allow for detection of local hydrogen-rich features that can be associated with geological structures. The FREND neutron telescope (Mitrofanov et al., 2018) onboard ExoMars TGO (Vago et al., 2015) is capable of a much better spatial resolution for mapping neutron emission of Mars. In this Report we present an analysis of the most intriguing local area of highly suppressed neutron emission in the vicinity of the Martian equator, which coincides with Candor Chaos in the central area of Valles Marineris, thought to be promising for testing water ice (Gourronc et al., 2014). Provided such suppression would be interpreted as the evidence for very high content of hydrogen in the soil, the mean water equivalent hydrogen value in the local suppression area should be as large as 40.3 wt%. This finding is thought to be uncommon for equatorial regions, but is probably associated with particular geomorphological conditions inside Valles Marineris.