P058-03
Thermomechanical Properties of the Shallow Martian Regolith
Monday, 14 December 2020: 08:38
Virtual
Kenneth J Hurst1, Li Lin2, Rudolf Widmer-Schnidrig3, Matt Golombek4, Simon C Staehler5, John-Robert Scholz6, Martin van Driel7, Anna Mittelholz8, Catherine Johnson9, Mark T Lemmon10, Ralph D Lorenz11, Philippe Henri Lognonné12, Nils Tobias Mueller13, Laurent Pou14, Aymeric Spiga15, Donald J Banfield16, Savas Ceylan5, Constantinos Charalambous17, John F. Clinton18, Domenico Giardini19, Francis Nimmo20, Mark P Panning21, Walter E Zuern3 and William Bruce Banerdt4, (1)Jet Propulsion Lab / Caltech, Pasadena, CA, United States, (2)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, United States, (3)Black Forest Observatory, Wolfach, Germany, (4)JPL/NASA/Caltech, Pasadena, CA, United States, (5)ETH Zurich, Zurich, Switzerland, (6)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (7)ETH Zurich, Department of Earth Sciences, Institute of Geophysics, Zurich, Switzerland, (8)University of British Columbia, Department of Earth, Ocean and Atmospheric Science, Vancouver, BC, Canada, (9)University of British Columbia, Vancouver, BC, Canada, (10)Space Science Institute Boulder, Boulder, TX, United States, (11)JHU / APL, Laurel, MD, United States, (12)Université de Paris, Institut de physique du globe de Paris, CNRS, Paris, France, (13)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (14)University of California Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States, (15)LMD/IPSL, Sorbonne Université, Paris, France - Institut Universitaire de France, France, Palaiseau Cedex, France, (16)Cornell University, Center for Radiophysics and Space Research, Ithaca, NY, United States, (17)Imperial College London, London, SW7, United Kingdom, (18)ETH Swiss Federal Institute of Technology Zurich, Swiss Seismological Service, Zurich, Switzerland, (19)Swiss Federal Institute of Technology (ETH), Zurich, Switzerland, (20)University of California-Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States, (21)Univ of FL-Geological Sciences, Gainesville, FL, United States
Abstract:
The seismometer placed on the surface of Mars by the InSight mission recorded signals associated with partial solar eclipses by Phobos. These signals are consistent with tilts of the seismometer. Efforts to model these tilts as a thermoelastic response to a thin (0.5-1.0 mm) layer cooling during the eclipse have shown that one way to achieve the observed tilts is to have a near-surface layer of enhanced rigidity. Another way is to have a local inhomogeneity (perhaps a buried rock) that couples the local strain field into tilts. Observations of the vertical walls of pits formed by the descent rocket blast, and around the Heat-flow and Physical Properties Probe, indicate a near-surface layer that has high cohesion that is at least several cm thick. Geologically, these steep walls with high cohesion are interpreted as duricrust which forms in sediments where small amounts of water from the atmosphere create Sulphur and Chlorine salts, depositing them at grain boundaries, weakly cementing the grains together. If we interpret the tilts during the eclipse as a response to the duricrust, we can place constraints on the relative contrast in the rigidity between the duricrust layer and the sediments below, or the thickness of the duricrust. We present an exploration of this parameter space.
