Radiative Transfer in the Martian Environment: In-Situ Results from the MSL Curiosity Rover and Laboratory Experimentation on Martian Regolith and Crystalline Rock Analogs

Global circulation models predicted a suppressed planetary boundary layer within Gale Crater prior to the landing of the Mars Science Laboratory. Images from Mars allow the amount of suspended dust near the crater floor to be estimated numerically. The atmosphere within the crater is shown to be relatively dust free compared to the amount of dust inferred in the atmospheric column, suggesting little mixing between the upper and lower layers. The dust within the crater appears to be well mixed horizontally, implying that dust events (such as dust devils or lateral dust transport) in the northern plains of Gale Crater are rare, even during the most convective time of day. This supports the notion of a suppressed planetary boundary layer within Gale Crater.

Radiative transfer modeling of the martian atmosphere benefits from this quantification of low-lying dust. This dissertation aims to expand our knowledge of the radiation environment of Mars into its surface and subsurface.

The scattering of radiation through analog martian materials is an area with little research. A mini-goniometer is built to collect transmission spectra as a function of scattering angle for martian analog regoliths and crystalline rock samples. Materials show strong forward or isotropic scattering profiles through the samples. The transmission through the materials is assessed at ultraviolet and visible wavelengths. Kieserite and the majority of the rock samples exhibit an isotropic scattering profile and attenuate ultraviolet radiation significantly.

Ultraviolet shielding materials are potential ecological niches for biosignatures, and this dissertation aims to guide the search for these environments on present day Mars.

Studies into the habitability of martian surface analogs typically assess the amount of radiation transmitting perpendicular into a surface. This does not fully characterize the multiple surface scattering that exists within these materials. The depths at which radioresistant microorganisms can exist on present day Mars are estimated by modeling the isotropic transmission scattering profiles for kieserite and crystalline rocks under martian insolation. A depth between 2 and 10 mm into the martian subsurface is enough to attenuate ultraviolet radiation to levels suitable to terrestrial radioresistant microorganisms.