Dust Lifting Through Surface Albedo Changes at Jezero Crater, Mars

Abstract We have identified temporal variations in surface albedo at Jezero Crater using first-of-their-kind high-cadence in-situ measurements of reflected shortwave radiation during the first 350 sols (Martian days) of the Mars 2020 mission. Simultaneous MEDA measurements of pressure, radiative fluxes, winds and sky brightness indicate that these albedo changes are caused by encounters with dust devils (dusty convective vortices) under typical conditions and by a dust storm that affected Jezero (sols 313-318). Albedo changes caused by dust devils are more frequent, but their magnitude is smaller compared to that caused by the storm. Spectral reflectance measurements from Mastcam-Z images indicate that the decrease in albedo is mainly caused by dust removal. The intensity, size and trajectory of the convective vortex, as well as the availability and mobility of small particles at the surface, play a role in the ability of detecting albedo changes from MEDA measurements. These results show synergies between multiple instruments (MEDA, Mastcam-Z, Navcam and Supercam microphone) to improve our understanding of aeolian processes on Mars. 1. Introduction The Martian atmosphere interacts with the surface, redistributing dust and sand particles (Kahre et al., 2017). Dust particles are lifted by convective vortices and by strong wind gusts, and are subsequently transported before settling again (Newman et al., 2002a; Newman et al., 2002b; Basu et al., 2004; Kahre et al., 2006; Vicente-Retortillo et al., 2018). The redistribution of small particles modifies the surface albedo (Wells et al., 1984; Szwast et al., 2006; Reiss et al., 2010). Since February 2021, the environmental conditions at Jezero Crater have been monitored by the Mars Environmental Dynamics Analyzer (MEDA), the suite of meteorological sensors onboard the Mars 2020 Perseverance rover (Rodriguez-Manfredi et al., 2021; Farley et al., 2020). Simultaneous measurements from the Thermal and Infrared Sensor (TIRS), the Radiation and Dust Sensor (RDS), the Pressure Sensor and the Wind Sensor allow studying dust lifting at the Martian surface by analyzing an unprecedented set of magnitudes, including high frequency measurements (1 – 2 Hz) of surface broadband albedo and temperature, wind speed and direction, downwelling radiation, sky radiance and pressure. In addition, Mastcam-Z (Bell et al., 2021) and Navcam (Maki et al., 2020) images allow quantitative estimations of the spectral reflectance of the surface and provide additional visual context of the rover surroundings. Finally, recordings of the Supercam microphone (Maurice et al., 2021) provide additional information on winds during some periods for which MEDA measurements are not available. Surface albedo changes have been typically analyzed using satellite measurements (Cantor et al., 2006; Whelley and Greeley, 2008; Greeley et al., 2010; Reiss et al., 2016; Geissler et al., 2016; Wellington and Bell, 2020). These studies provide relevant information about the temporal and spatial variability of dust lifting processes. However, satellite observations generally lack of contemporaneous near-surface environmental measurements and have a low temporal coverage at a given location. Albedo has also been studied using images acquired by landed missions (Greeley et al., 2005; Bell III et al., 2008; Rice et al., 2018). Images provide a good context of the terrain, but due to their nature, they require more energy and storage availability than a single albedo value. Due to their limited temporal coverage and to the rover motion, these studies are typically focused on spatial variations in albedo. Here we use MEDA measurements to analyze for the first time environmental variables coincident (temporally and spatially) with the dust lifting event that leads to a change in surface albedo, providing insights into dust lifting mechanisms and effects on the surface, as well as ground-truth for orbital observations. Jezero Crater was affected by a dust storm between sols 313 and 318 of the mission (Ls ~155º), which caused a significant change in environmental conditions. The rover remained at the same location between sols 287 and 328, providing a unique opportunity to study the surface albedo and temperature before, during and after the storm. Section 2 describes the Mars 2020 instruments that provided the measurements for this work and the methodology to analyze the albedo changes. Sections 3 and 4 are dovoted to the surface albedo changes under typical conditions and during a dust storm, respectively. In Section 5, we provide an overall discussion of the variables involved in surface albedo changes. Finally, we highlight the main results of this work in Section 6.