Mars Dust Micromechanics: Mer Marsdial and Laboratory Observations

Introduction: In future human exploration of Mars, many challenges face us. Mars is a dusty planet and dust and windblown particulates will present one of the most significant difficulties [1]. The dust and granular regolith will challenge materials, machines, and people. Our experience with dust-covered astronauts on the Moon and with landers and rovers on Mars suggests that significant efforts will be needed to sustain human exploration in this hostile environment. In 2002, the National Research Council examined precursor measurements required for the safe human exploration of Mars [2]. They recommended “NASA should determine the adhesive properties of Martian soil and airborne dust in order to evaluate the effects of dust adhesion on critical systems. This characterization must be conducted in situ by means of experiments to measure airborne dust adhesion.” Solar power, critical to long-term Martian exploration, is compromised by daily settling of dust on solar panel surfaces. The abrasive quality of the Martian soil, quantified during the Pathfinder Mission, is noted as another significant risk of exploration. Many physical health risks from Mars dust are also anticipated. Martian and Lunar dust simulants have shown pulmonary toxicity in laboratory tests of exposed mice [3]. Apollo astronauts experienced compromising effects of Lunar dust on their spacesuits and inside their lander, where dust irritated their eyes and lungs in the low gravity environment. Research has shown smaller particulates can have an angle of repose, θr , that is affected by electrostatic interactions as well as environmental conditions [4]. Charging of Mars airborne particulates is likely, due to triboelectric or photoelectric processes, and electrical ground conduction at the Mars surface will be small with only trace water. Frictional forces on Mars will be 37.8% of those on Earth due to gravity, and this force change can contribute to modifying granular dynamics and statics on Mars, especially for larger particles and granules. We previously observed repeating patterns of fine sand deposition on cylindrical and spherical surfaces and developed a novel approach to extract granular micromechanics data of Mars dust surrogates [5-6]; this data compares well with published results that use classical methods. Round surfaces have continuously increasing tangential angles for particle repose and can provide an approach for small particle, granular micromechanics study. Knowledge of the angle of repose of Martian dust and granular regolith, θr , will be useful in the design of exploration and support systems, and may provide a natural bulk dust removal technique for surfaces engineered beyond that angle. Increasing our knowledge of Martian granular dynamics is important considering the transport of surface materials for construction and harvesting of planetary minerals for sustainable exploration. A Mars dust angle of repose instrument was incorporated into the cancelled 2001 NASA Mars Surveyor Lander and the crash-landed 2003 ESA Beagle 2 Lander [7]. The overall goal of the research presented here is to test new approaches for understanding Mars dust dynamics and statics in laboratory simulations and for Mars lander configurations. We examine Mars Exploration Rover (MER) dust deposition images and laboratory data of regolith simulants to better understand Mars dust micromechanics. Materials and Methods: MER Pancam and calibration images were obtained from NASA. Image anlysis used image analysis software and the trigonometric model previously developed [5, 6]. Laboratory simulations used a Mars dust environmental chamber (MDEC) and methods previously described [8].