Search

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 μm 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. Key Points: Soil crusts are prevalent across the Jezero crater floorSoil surfaces are largely hydratedSoil crusts likely contain salts and may form during changes in atmospheric relative humidity at the surface [ABSTRACT FROM AUTHOR]

Mars 2020 Mars Environmental Dynamics Analyzer (MEDA) instrument data acquired during half of a Martian year (Ls 13°–180°), and modeling efforts with the Mars Regional Atmospheric Modeling System (MRAMS) and the Mars Climate Database (MCD) enable the study of the seasonal evolution and variability of nocturnal atmospheric turbulence at Jezero crater. Nighttime conditions in Mars's Planetary Boundary Layer are highly stable because of strong radiative cooling that efficiently inhibits convection. However, MEDA nighttime observations of simultaneous rapid fluctuations in horizontal wind speed and air temperatures suggest the development of nighttime turbulence in Jezero crater. Mesoscale modeling with MRAMS also shows a similar pattern and enables us to investigate the origins of this turbulence and the mechanisms at play. As opposed to Gale crater, less evidence of turbulence from breaking mountain wave activity was found in Jezero during the period studied with MRAMS. On the contrary, the model suggests that nighttime turbulence at Jezero crater is explained by increasingly strong wind shear produced by the development of an atmospheric bore‐like disturbance at the nocturnal inversion interface. These atmospheric bores are produced by downslope winds from the west rim undercutting a strong low‐level jet aloft from ∼19:00 to 01:00 LTST and from ∼01:00 LTST to dawn when undercutting weak winds aloft. The enhanced wind shear leads to a reduction in the Richardson number and an onset of mechanical turbulence. Once the critical Richardson Number is reached (Ri ∼ <0.25), shear instabilities can mix warmer air aloft down to the surface. Plain Language Summary: Mars is highly susceptible to atmospheric turbulence, which refers to the chaotic and instantaneous variation in the thermodynamic magnitudes of the atmosphere. While the Martian nighttime conditions near the surface are typically stable due to strong radiative cooling that efficiently inhibits convection, turbulence can still occur due to wind shear. Wind shear is defined as a change in wind speed and/or direction over a relatively short distance in the atmosphere. This phenomenon can mechanically force turbulence as described in this study using both Mars 2020 rover observations at Jezero crater and numerical modeling efforts. Both observations and modeling show turbulence during the first part of the night and around midnight during most of the times of the year with a clear hiatus in turbulence centered prior to summer solstice. We provide evidence that points toward the wind shear turbulence being caused by atmospheric bore waves inside the crater. Key Points: Nocturnal turbulence at Jezero crater peaks at Ls ∼ 37, Ls ∼ 56, and Ls ∼ 123 with a clear hiatus lasting tens of sols centered at Ls ∼ 83Both observations and modeling show turbulence during the first part of the night and around midnightTurbulence is produced by wind shear originating from the passage of an atmospheric bore wave related to downslope winds from the west rim [ABSTRACT FROM AUTHOR]

We study the diurnal cycle of rapid thermal fluctuations observed by the Mars Environmental Dynamics Analyzer, onboard the Perseverance rover at Jezero Crater, as a function of local time and season. In this context, rapid refers to periods between 15 min and half a second. Some insight is also provided into wind fluctuations that are the base for most of the existing theories on turbulent flows. The results expand the observations from previous Mars missions, namely Viking, Mars Pathfinder, and Phoenix, and they add to our knowledge of near‐surface fluctuations on Mars. (a) Probability distribution functions of the fluctuations are determined and found to have exponential tails. This means that models that represent the interaction within the environment and with the surface as a stochastic forcing need to account for the sudden events responsible for the exponential tails. (b) Power density spectra are calculated and show several dynamical regimes with different slopes associated to forcing, an intermediate regime, and a higher frequency regime. All change with time of the day. The results imply that the fastest regime is not a universal scenario for the temperature fluctuations near the surface. (c) The scale dependence of the fluctuations confirms the existence of intermittent outbursts associated to the slower fluctuations, possibly associated to the larger scale structures, and explains why the spectral density slopes do not follow Kolmogorov's law. Understanding the role of larger scale structures would help refine scaling theories of the near‐surface Martian atmosphere and its interactions with the surface. Plain Language Summary: The Martian atmosphere is mostly driven by solar radiative forcing that also controls how it interacts with the surface. Atmospheric phenomena respond within seconds to years, but models can only resolve limited ranges of these time scales. This work explores how temperature fluctuates at time scales faster than what models typically resolve, and how this variability affects phenomena at the time scales that they resolve. The statistical properties of rapid environmental changes, or fluctuations, caused by solar forcing help us understand how the lowest atmosphere and surface evolve and interact. Theories that have been tested on Earth predicting how energy transfers or dissipates between the fast and slow dynamical regimes are explored here searching for rules that relate both regimes on another world. This work finds that fluctuations of air temperature and horizontal winds near the Martian surface do not follow probability distributions typical of normal random processes. The energy transfer rate is not consistent at scales faster than 10 s with a unique, or universal, rule relating fast to slow fluctuations. Finally, it suggests that this lack of universality is caused by intermittent disruptions through sudden large coherent structures, like convective vortices and waves, that influence how temperature dissipates. Key Points: Probability Distribution functions for temperature fluctuations at Jezero Crater on the time scale of seconds have exponential tailsPower density spectra of temperature fluctuations find at least two dynamical regimes that evolve differently with time of the daySudden outbursts, likely associated to coherent structures, disrupt intermittently the rate of temperature dissipation to the smaller scales [ABSTRACT FROM AUTHOR]

The Mars Environmental Dynamics Analyzer instrument on Mars 2020 has five Atmospheric Temperature Sensors at two altitudes (0.84 and 1.45 m) plus a Thermal InfraRed Sensor that measures temperatures on the surface and at ∼40 m. We analyze the measurements from these sensors to describe the evolution of temperatures in Jezero up to mission sol 400 (solar longitude LS = 13°–203°). The diurnal thermal cycle is characterized by a daytime convective period and a nocturnal stable atmosphere with a variable thermal inversion. We find a linear relationship between the daytime temperature fluctuations and the vertical thermal gradient with temperature fluctuations that peak at noon with typical values of 2.5 K at 1.45 m. In the late afternoon (∼17:00 Local True Solar Time), the atmosphere becomes vertically isothermal with vanishing fluctuations. We observe very small seasonal changes in air temperatures during the period analyzed. This is related to small changes in solar irradiation and dust opacity. However, we find significant changes in surface temperatures that are related to the variety of thermal inertias of the terrains explored along the traverse of Perseverance. These changes strongly influence the vertical thermal gradient, breaking the nighttime thermal inversion over terrains of high thermal inertia. We explore possible detections of atmospheric tides on near‐surface temperatures and we examine variations in temperatures over timescales of a few sols that could be indicative of atmospheric waves affecting near‐surface temperatures. We also discuss temperatures during a regional dust storm at LS = 153°–156° that simultaneously warmed the near surface atmosphere while cooling the surface. Plain Language Summary: The Mars Environmental Dynamics Analyzer instrument on the Mars 2020 Perseverance rover records temperatures in Jezero at four altitudes from the surface to 40 m. We describe the evolution of temperatures over the first 400 Martian days of the mission from northern spring to early autumn. Diurnal temperatures show an unstable convective regime during the daytime and a stable atmosphere at night. Daytime convection produces thermal fluctuations that peak at noon with typical values of 2.5 K at 1.45 m. These thermal fluctuations vanish in the late afternoon when an isothermal atmosphere is observed from the surface up to 40 m. We also find a linear relationship between the daytime temperature fluctuations and the thermal gradient between the surface and the atmosphere. We find very little seasonal change in air temperatures. However, the thermal inertia of the terrain affects surface temperatures, and the nighttime thermal inversion breaks over terrains with high thermal inertia. We investigate the possible detection in near surface temperatures of thermal tides and atmospheric waves. Finally, we show the thermal response of the surface and the atmosphere during the passage of a regional dust storm with a simultaneous cooling of the surface and warming of the near‐surface atmosphere. Key Points: Surface and atmospheric temperatures at Jezero show small seasonal variations from Spring to early Autumn that agree with modelsThe intensity of daytime convective fluctuations is correlated with vertical thermal gradients, which depend on the surface thermal inertiaA dust storm significantly heated the lower atmosphere while cooling the surface indicating strong radiative effects of low altitude dust [ABSTRACT FROM AUTHOR]