Surface Energy Budget, Albedo, and Thermal Inertia at Jezero Crater, Mars, as Observed From the Mars 2020 MEDA Instrument

Abstract

The Mars Environmental Dynamics Analyzer (MEDA) on board Perseverance includes first-of-its-kind sensors measuring the incident and reflected solar flux, the downwelling atmospheric IR flux, and the upwelling IR flux emitted by the surface. We use these measurements for the first 350 sols of the Mars 2020 mission (L s ∼ 6°-174° in Martian Year 36) to determine the surface radiative budget on Mars and to calculate the broadband albedo (0.3-3 μm) as a function of the illumination and viewing geometry. Together with MEDA measurements of ground temperature, we calculate the thermal inertia for homogeneous terrains without the need for numerical thermal models. We found that (a) the observed downwelling atmospheric IR flux is significantly lower than the model predictions. This is likely caused by the strong diurnal variation in aerosol opacity measured by MEDA, which is not accounted for by numerical models. (b) The albedo presents a marked non-Lambertian behavior, with lowest values near noon and highest values corresponding to low phase angles (i.e., Sun behind the observer). (c) Thermal inertia values ranged between 180 (sand dune) and 605 (bedrock-dominated material) SI units. (d) Averages of albedo and thermal inertia (spatial resolution of ∼3-4 m 2 ) along Perseverance's traverse are in very good agreement with collocated retrievals of thermal inertia from Thermal Emission Imaging System (spatial resolution of 100 m per pixel) and of bolometric albedo in the 0.25-2.9 μm range from (spatial resolution of ∼300 km 2 ). The results presented here are important to validate model predictions and provide ground-truth to orbital measurements. Plain Language SummaryWe analyzed first-of-its-kind measurements from the weather station on board NASA's Perseverance rover. These include the incident solar radiation and the amount that is reflected by the surface, as well as the thermal atmospheric forcing (greenhouse effect) and the thermal heat released by the surface. These measurements comprise the radiant energy budget, which is fundamental to understanding Mars' weather through its impact on temperatures. From the solar measurements, we obtained the surface reflectance for a variety of illuminating and viewing geometries. We found that the thermal atmospheric forcing is weaker than expected from models, likely because of the strong diurnal variation in atmospheric aerosols observed by the rover, which is not accounted for by models. We also found that the surface reflectance is not uniform from all directions, but that it decreases when the Sun is highest in the sky (near noon) and increases when the Sun is directly behind the observer (sunset and sunrise), and thus the shadows cast by their roughness elements (e.g., pores and pits) are minimized. Because models neither consider diurnal variations in atmospheric aerosols nor in the surface reflectance, the results presented here are important to validate model predictions for future human exploration. MARTÍNEZ ET AL.

Dust Lifting Through Surface Albedo Changes at Jezero Crater, Mars

“…In the case of the dust devils, the relationship between the decreases in solar radiation and surface temperature is not straightforward. The weak correlation could be partly explained by the different thermophysical properties of the terrain across the rover traverse (Martínez et al., 2023). The solar energy deficit and the temperature decrease of the second dust devil on sol 57 were similar to the values during the Phobos eclipses, suggesting that in this case the temperature change could be explained mostly by the radiative imbalance.…”

“…We use the ratio between TIRS IR3 and RDS TOP7 measurements as a proxy for surface albedo (note that the values do not correspond to the actual albedo because TIRS and RDS measure in different spectral bands, but it is valid for our purpose of analyzing relative temporal variations; actual albedo values accounting for the difference in bands are shown in Martínez et al., 2023). We have applied two different methods to detect albedo changes.…”

Near Surface Atmospheric Temperatures at Jezero From Mars 2020 MEDA Measurements

“…Panel b shows the corresponding analysis for the nighttime, in which no correlation between temperature fluctuations and the atmospheric stability is apparent. This is a consequence of the nighttime temperature fluctuations not being driven by the sensible heat flux, which is negligible at night compared with the radiative fluxes (Martínez et al., 2023).…”

“…Figure 7c shows thermal inertia and albedo values of the different terrains explored by Perseverance as a function of time. These values come from MEDA retrievals in Martínez et al (2023), who uses a combination of TIRS and Radiation and Dust Sensor measurements. TIRS measurements characterize an area of 3 m 2 , which is the FoV of its downward looking channel.…”

Diurnal and Seasonal Variations of Aerosol Optical Depth Observed by MEDA/TIRS at Jezero Crater, Mars

“…A. Rodriguez‐Manfredi et al., 2021). A set of MEDA sensors, collectively called the Thermal Infrared Sensor (TIRS), has the goal of measuring the upward and downward radiation fields and energy budget at the surface (Martínez et al., 2023; Pérez‐Izquierdo et al., 2018; Sebastián et al., 2020, 2021).…”