An Examination of Soil Crusts on the Floor of Jezero Crater, Mars

Martian soils are critically important for understanding the history of Mars, past potentially habitable environments, returned samples, and future human exploration. This study examines soil crusts on the floor of Jezero crater encountered during initial phases of the Mars 2020 mission. Soil surface crusts have been observed on Mars at other locations, starting with the two Viking Lander missions. Rover observations show that soil crusts are also common across the floor of Jezero crater, revealed in 45 of 101 locations where rover wheels disturbed the soil surface, two out of seven helicopter flights that crossed the wheel tracks, and four of eight abrasion/drilling sites. Most soils measured by the SuperCam laser-induced breakdown spectroscopy (LIBS) instrument show high hydrogen content at the surface, and fine-grained soils also show a visible/near infrared (VISIR) 1.9 mu m H2O absorption feature. The Planetary Instrument for X-ray Lithochemistry (PIXL) and SuperCam observations suggest the presence of salts at the surface of rocks and soils. The correlation of S and Cl contents with H contents in SuperCam LIBS measurements suggests that the salts present are likely hydrated. On the "Naltsos" target, magnesium and sulfur are correlated in PIXL measurements, and Mg is tightly correlated with H at the SuperCam points, suggesting hydrated Mg-sulfates. Mars Environmental Dynamics Analyzer (MEDA) observations indicate possible frost events and potential changes in the hydration of Mg-sulfate salts. Jezero crater soil crusts may therefore form by salts that are hydrated by changes in relative humidity and frost events, cementing the soil surface together. Plain Language Summary Martian soils are important for understanding the history of Mars as well as future sample return and human exploration. Soil crusts in Jezero crater, which are also broadly found across Mars, can be observed when they are disturbed, such as by rover wheels or coring/abrasion activities. Jezero crater soil crusts are examined using images from the Perseverance and Ingenuity cameras, as well as using data from the SuperCam, PIXL, Mastcam-Z, and MEDA instruments. Soil crusts are common in Jezero crater and show characteristics including hydration at the surface and the presence of salts that might contain water. MEDA instrument measurements indicate that changes in the hydration state of salts may result during conditions measured at Jezero crater. Jezero crater soil crusts may therefore form by salts that are present on the surface that can add or lose water during changes in relative atmospheric humidity and frost events. These changes in the amount of water present in the salts may result in soil surfaces that are cemented together, forming the crusts observed at Jezero crater. A better understanding of Mars soil crusts will help in the understanding of samples returned to Earth from Mars, as well as future human exploration.