Speaker
Description
Studying the Martian subsurface water-equivalent hydrogen (WEH) content is crucial for understanding the environmental conditions that prevailed on early Mars, addressing the question of whether life ever existed or still exists, and identifying potentially habitable environments for future colonization. The standard method for determining the water content involves measurements of neutron albedo or γ-rays generated by interactions of Galactic Cosmic Rays (GCRs) with the Martian soil. However, these interactions also produce albedo protons, which likewise depend on the subsurface composition. The higher the WEH content in the soil, the lower the albedo proton flux, and vice versa. Assessing albedo protons could potentially open an entirely new window for inferring subsurface WEH content on Mars.
The Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) is the only instrument on the Martian surface capable of resolving the directionality of 100–200 MeV protons. Using a branching integration technique, we extract an uncontaminated albedo proton signal. This signal is subsequently corrected for solar modulation effects to obtain a pure albedo proton flux that presumably depends solely on the Martian subsurface composition. Investigations in the Marker Band Valley and in the Greenheugh Pediment - regions along the MSL path expected to be wetter and drier than usual, respectively - suggest that MSL/RAD could be sensitive to subsurface WEH content changes even up to 10%. Comparison with measurements from the Dynamic Albedo of Neutrons (DAN) instrument onboard MSL, as well as supporting GEANT4 simulations, will show whether this result is a coincidence or a true dependence.
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