The Thermophysical Variability of the Vera Rubin Ridge as Explored by the Mars Science Laboratory

The thermophysical properties of planetary surfaces have the potential to help illuminate key characteristics that cannot be addressed otherwise. Specifically, by detailed analysis of the thermal inertia (TI) both from orbit and landed assets a robust understanding of the particle sizes, degree of induration, and surface physical properties can be derived. These parameters can be used to place important constraints on present and past environments including key environmental transitions. As the Mars Science Laboratory (MSL) Curiosity rover has continued its traverse up Aeolis Mons, it has explored a variety of past aqueous environments and a significant range of TI values (e.g. 150-550+ J m^-2 K^-1 s^-1/2). More specifically, as Curiosity transitioned upslope through the Murray formation to the Vera Rubin Ridge (VRR) member, significant differences in TI, but not necessarily particle size (mostly below the resolution limits of the Mars Hand Lens Imager (MAHLI)) have been noted. The VRR has the highest orbitally-derived TI from the Thermal Emission Imaging System (THEMIS) encountered by MSL to date; however, the cause of elevated TI, especially when considering the fine-grained rocks, lack of obvious sedimentological and geochemical changes between units, remains unknown.

In this effort, we present a continuing thermophysical record derived by the MSL REMS Ground Temperature Sensor (GTS) following well-established methods. We compare these results to the thermophysical properties and particle sizes derived from THEMIS, and link these measurements to ground truth particle size upper limits determined from MAHLI images. We consider a variety of thermophysical scenarios, including subsurface layering/fracturing, lateral heterogeneity, and pore filling cements that would increase the TI beyond what is expected for loose particulates. We compare these scenarios with the context provided by other rover observations (e.g. presence of concretions, veins, scarps, changes in texture, morphology, or composition, etc.). Importantly, given the lack of an obvious grain size transition from the Murray formation to the Vera Rubin Ridge, we will provide estimates on the fraction of extra cements to account for the increased thermal inertia over the mudstone underlying the Vera Rubin Ridge.