The Mars Exploration Rovers (MER), Spirit and Opportunity, landed on Mars in 2004 just weeks apart. Using spectra from the Miniature Thermal Emission Spectrometer (Mini-TES), both rovers were able to sample the lowest 2 km of the vertical temperature profile of the atmosphere. During a single observation for Mini-TES, spectra were taken every two seconds with observations lasting up to 42 minutes. While results up to this point have averaged the spectra together to retrieve information on dust, water vapor and temperature, individual temperature retrievals are possible every two seconds and contain information on short timescale atmospheric fluctuations. These fluctuations are indicative of boundary layer behavior at each site. We have retrieved the vertical temperature profile from individual spectra and have used these profiles to assess boundary layer conditions at each rover location. We will present temperature profiles from individual retrievals and identify and characterize fluctuations within these profiles. We will also show the seasonal variation of these fluctuations over the first 1200 sols (nearly 2 Mars Years) for both Spirit and Opportunity rovers.

IntroductionThe Emirates Mars InfraRed Spectrometer (EMIRS) instrument onboard the Emirates Mars Mission (EMM) “Hope” probe is a Fourier Transform Infrared spectrometer that has been observing the Martian surface and atmosphere between 6 and 100 μm since February 2021 [1, 2]. The unique orbit of EMM allows EMIRS to observe the entire Martian disk at each observation, covering all the surface of the planet in ~4 orbits, which corresponds to ~5° of Ls, or 10 Earth days.[3] used the surface temperature retrievals from EMIRS to detect and monitor the presence of H2O and CO2 ice on the surface of the planet, including the temporal and local time evolution of the CO2 frost that can appear at Martian equatorial latitudes. This frost has been observed in the second half of the night around the equinoxes. Small crystals and optically thin layers are expected from the work of [4] using THEMIS data. However, as EMIRS provides fully resolved spectra whereas THEMIS is a multi-band instrument, we will be able to strengthen the constraints on the physical properties of these deposits. And monitor for the first time the evolution of the ice properties during its condensation phase from 12 a.m. to 6 a.m. thanks to the unique temporal coverage of EMM instruments.Data & MethodsBased on the first identification of the EMIRS pixels mostly covered by CO2 ice presented in [3], we use here the full spectroscopic power of the instrument to characterize and constrain the physical properties of these icy deposits (crystal size, thickness) and their temporal evolution. First, we identify areas where CO2 surface frost has been detected at different local times over a few degrees of Ls(to have a sufficient spatial and temporal coverage), then we bin the data over temporal bins of 1-hr and compare the averaged spectra for each bin. The spatial extent of the EMIRS pixel footprints is computed using the SPiP Python module [5].ResultsFirst, we observe that CO2 ice spectral signatures are observed in the EMIRS spectra when predicted by the temperature criterion, between midnight and 6 a.m., but mostly from 3 a.m. Comparison of spectra presented in Figure 1a with models from [4] may suggest optically thin layers of CO2 ice, with a thickness of ~ 100 μm, when models can predict condensation of up to a few tens of microns of ice just before sunrise.As the surface temperature remains below the freezing point of CO2 during the second half of the night, and CO2 is always available at the surface from the atmosphere, condensation is expected to occur over the night hours. However, no significant temporal variations of the spectra have been observed over the night. The differences between spectra that can be seen in Figure 1 are mostly associated with spatial variability of the surface emissivity, as can be seen on panels c & d. This is not in favor of the scenario of an accumulation of ice over the night which would increase progressively the frost thickness and/or the size of the crystals. Thus, the lack of variability over the night may suggest that the condensation may occur within the surface regolith and/or the subsurface, as suggested by [6].Figure 1: EMIRS spectra from EMM orbits 171 to 180 where surface CO2 frost has been detected between 150°W and 90°W and between 0°N and 60°N (North of Tharsis), averaged over temporal bins of 1-hr (a) and footprints of the considered EMIRS pixels (b). The colors of the spectra and pixels indicate the local time range for the observations. (c & d) EMIRS average spectrum and pixel footprints over the same region for observations between 11 a.m. and 1 p.m. to provide a daytime emissivity reference to be compared with the nighttime spectra.Conclusion & PerspectivesIn this work, we present the first spectroscopic monitoring of surface nighttime CO2 frost under equatorial latitudes as a function of the local time. We do not observe significant variation of the spectra over the night but a spatial variability is present. This suggests that the frost condensation likely occurs within the regolith and/or close subsurface rather than a simple accumulation of ice at the surface overnight. Further spectral modeling of the emissivity will be needed to assess the physical properties of these deposits considering different scenarios including notably: “dirty” CO2 ice, subsurface CO2 ice, or slab of CO2 ice.AcknowledgmentsThis work was funded by the Emirates Mars Mission project under the Emirates Mars Infrared Spectrometer instrument via The United Arab Emirates Space Agency (UAESA) and the Mohammed Bin Rashid Space Centre (MBRSC).A. S. also acknowledges funding by CNES.References[1] Amiri, H. E. S. et al. (2022), SSR, 218, 4. [2] Edwards, C. S. et al. (2021), SSR, 217, 77. [3] Stcherbinine, A. et al. (2023), GRL, 50, e2023GL103629. [4] Piqueux, S. et al. (2016), JGR: Planets, 121, 1174-1189. [5] Stcherbinine, A. (2023), Zenodo, doi:10.5281/zenodo.7714204. [6] Lange, L. et al. (2022), JGR: Planets, 127, e2021JE006988.

<p>The Mars Global Surveyor (MGS) mission carried a spectrometer and bolometer as part of the Thermal Emission Spectrometer (TES) instrument package. While the spectrometer ceased operations in early Mars Year (MY) 37 due to aging of the required neon lamp, the bolometers continued to operate for nearly a full Mars year. This time-period covered the MY 27 dust storm season and most of the MY 28 aphelion cloud belt season. TES consisted of a spectrometer with two additional broadband bolometers in the visible (0.3-3.0 µm) and infrared (5-100 µm). Observations were taken with both the spectrometer and bolometer simultaneously for nearly three Mars years prior to degradation of the neon lamp. The observational cadence during the bolometer-only extended mission alternated between one orbit of nadir observations and one orbit of limb observations. We will present results for the vertical distribution of atmospheric aerosol optical depth retrieved from the TES bolometer limb observations prior to the extended mission when spectrometer data (and previous retrievals) are available to inform the results. In addition, we will provide examples of retrieved vertical distribution of aerosol optical depth for observations taken in the bolometer-only extended mission for comparison.</p>

<p>The Thermal Infrared Sensor (TIRS; Sebastián et al., 2021; Martínez et al., 2023) is one of the six sensor packages of the Mars Environmental Dynamics Analyzer (MEDA; Rodríguez-Manfredi et al., 2021), which in turn is one of the seven science instruments on board Perseverance. Here we show a summary of TIRS scientific highlights during the first Martian year of operations. In particular, TIRS is providing the first in situ determination of the surface radiative budget, direct determination of broadband albedo and thermal inertia (Martínez et al., 2023; Savijärvi et al., 2022), and around-the-clock determination of aerosol opacities (Smith et al., 2023). In addition, TIRS is providing ground-truth to orbital retrievals of thermal inertia and albedo, as well as geophysical characterization of the uppermost surface of the regolith during Phobos and Deimos eclipses. In synergy with other instruments, TIRS is being used to determine vertical profiles of temperature (Munguira et al., 2023), to detect dust lifting from sudden changes in albedo (Vicente-Retortillo et al., 2023), and to assess changes in the water content of the Martian soil (Hausrath et al., 2023), including the potential formation of frost.</p> <p>TIRS observations are critical to achieve MEDA’s first programmatic objective (validate global atmospheric models by measuring the radiative surface budget in preparation for future human exploration). Also, TIRS observations are important in support of flights of Ingenuity and therefore for the design and operations of future drones. </p> <p><strong>References</strong>:</p> <p>Hausrath, E. M. et al. (2023), The SuperCam team and the Regolith working group, An Examination of Soil Crusts on the Floor of Jezero crater, Mars, Journal of Geophysical Research: Planets (accepted).</p> <p>Martínez, G. M. et al. (2023), Surface Energy Budget, Albedo and Thermal Inertia at Jezero Crater, Mars, as Observed from the Mars 2020 MEDA Instrument, <em>Journal of Geophysical Research: Planets</em> (accepted).</p> <p>Munguira, A. et al. (2023), Near Surface Atmospheric Temperatures at Jezero from Mars 2020 MEDA measurements, Journal of Geophysical Research: Planets (under review).</p> <p>Rodriguez-Manfredi, J.A. et al. (2021), The Mars Environmental Dynamics Analyzer, MEDA. A suite of environmental sensors for the Mars 2020 mission, <em>Spa. Sci. Rev.</em>, 217(3), 1-86.</p> <p>Savijärvi, H. I. et al. (2022), Surface energy fluxes and temperatures at Jezero crater, Mars, Journal of Geophysical Research: Planets: e2022JE007438.</p> <p>Sebastián, E. et al. (2021), Thermal calibration of the MEDA-TIRS radiometer onboard NASA's Perseverance rover, <em>Acta Astronautica</em>, 182,144-159.</p> <p>Smith, M. D. et al. (2023), Diurnal and Seasonal Variations of Aerosol Optical Depth Observed by MEDA/TIRS at Jezero Crater, Mars, Journal of Geophysical Research: Planets (accepted).</p> <p>Vicente-Retortillo, A. et al. (2023), Dust Lifting Through Changes in Albedo at Jezero Crater, Mars, Journal of Geophysical Research: Planets (under review).</p>

The Emirates Mars Mission (EMM) Emirates Mars Infrared Spectrometer (EMIRS) currently around Mars is acquiring remote measurements of the martian surface (temperature and composition) and lower atmosphere. EMIRS is a FTIR spectrometer covering the range from 6.0-100 µm (1666-100 cm‑1) with a spectral sampling as high as 5 cm-1 with a 5.4-mrad IFOV. The EMIRS optical path includes a flat 45˚ pointing mirror to enable one degree of freedom while the spacecraft provides the other to build up a 2-dimensional array of observations. The primary goals of EMIRS are to characterize the geographic and diurnal variability of key atmospheric constituents (water ice, water vapor, and dust) along with temperature profiles and surface temperature on sub-seasonal timescales EMIRS acquires data of the full martian disk and thus provides an integrated view of the martian surface and atmosphere in every spectrum. These observations include complete diurnal, seasonal, and geographic coverage of atmospheric properties, surface temperature, and also surface composition/mineralogy at wavelengths not regularly acquired of the martian surface. Due to the unique nature of the EMM orbit, EMIRS also collects data that spans the full local solar time range (all solar incidence angles), at multiple emission angles. These unique observations permit the interrogation of diurnal surface ices/frost, thermophysics (including sub-surface layering from both a seasonal and diurnal skin depth), surface roughness, and rock abundance in addition to the primary science goals. In this presentation, we provide an overview of the first surface observations, atmospheric retrieval algorithm, and first atmospheric science results from the aphelion-season observations taken by EMIRS over the first several months of EMM Science Phase operations.

Clouds on Mars are primary elements for understanding the past and present climate of the planet. Cloud particles can affect the energy balance of the planet, and so the atmospheric dynamic, as well as influence the vertical distribution of dust particles through dust scavenging. The dust scavenging by clouds has critical consequences in the water cycle of the planet; e.g. regions in the atmosphere with insufficient quantity of dust particles (or condensation nuclei) can inhibit the formation of H2O clouds and thus lead to the presence of water vapor in excess of saturation [1]. The study of these interactions requires observations whose analysis allows us to infer simultaneously the properties of both the clouds and dust. To address these observations, the Radiation and Dust Sensor (RDS) [2] is part of the Mars Environmental Dynamics Analyzer (MEDA) [3] payload onboard of the Mars 2020 rover Perseverance. RDS instrument compromises two sets of 8 photodiodes (RDS-DP) and a camera (RDS-SkyCam). One set of photodiodes is pointed upward (TOP sensors), with each one covering a different wavelength range between 190-1200 nm. The other set is pointed sideways (LAT sensors), 20 degrees above the horizon, and they are spaced 45 degrees apart in azimuth to sample all directions at a single wavelength. In this work we will present the radiative transfer analysis of the RDS TOP sensors observations at twilight for the first 365 sols. The twilight period was selected to: i) better constrain the vertical distribution of dust particles for the cloud-free days; ii) detect aerosol layers with very low opacities (lower than 0.1); iii) estimate the cloud altitude [4]. We will discuss the implication of our observations and analyses for Mars aerosol structure and timescales. For example, we find a period of a few days with a notable increase in the presence of clouds during twilight, and for which we derived cloud altitudes higher than 40 km and settling timescales of a few hours (involving a rapid vertical transport of dust particles). References: [1] Maltagliati, Luca, et al. "Evidence of water vapor in excess of saturation in the atmosphere of Mars." science 333.6051 (2011): 1868-1871. [2] Apestigue, Victor, et al. "Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover." Sensors 22.8 (2022): 2907. [3] Rodriguez-Manfredi, José Antonio, et al. "The Mars Environmental Dynamics Analyzer, MEDA. A suite of environmental sensors for the Mars 2020 mission." Space science reviews 217.3 (2021): 1-86. [4] Toledo, D., et al. "Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)." Atmospheric Measurement Techniques 9.2 (2016): 455-467.

Thermal infrared observations made from the surface of Mars by the Perseverance rover and from orbit by the Emirates Mars mission enable the retrieval of dust aerosol optical depth at all local times, both day and night. Observations from the rover are useful for characterizing the localized, short timescale changes in dust optical depth, particularly during dust storms, while observations from the orbiter and useful for identifying global trends and temporal variations on longer timescales, from diurnal to seasonal. Together, these two vantage points provide complementary information that helps to understand the variations of dust over different temporal and spatial scales. 1. Introduction 1.1 Perseverance TIRS data: The Thermal InfraRed Sensor (TIRS) package on the Perseverance rover consists of five sensors used to characterize the upward and downward fluxes of visible and infrared radiation at the rover site (Rodriguez-Manfredi et al., 2021). Of interest here are the sensors TIRS IR1, which covers a broad portion of the thermal-infrared spectrum over the range 6–35 µm and TIRS IR2, which covers the CO2 band between 14.5 and 15.5 µm. Both sensors view upward at an elevation angle centered at 35° above the rover deck. As part of the MEDA suite of atmospheric sensors, TIRS observations are taken systematically throughout the sol at a frequency of 1 Hz. Observations in one-hour blocks are generally taken so that odd-numbered hours are covered on odd-numbered sols, while even-numbered hours are covered on even-numbered sols. In that way the entire 24-hour diurnal cycle is fully covered over a span of 2 sols. These observations are a part of the background baseline set for MEDA that runs essentially every day providing excellent diurnal and seasonal coverage. We use a radiative transfer model to compute the expected TIRS IR1 and IR2 signal for a given aerosol optical depth and temperature profile. We can then perform the retrieval by varying the atmospheric temperatures and aerosol optical depth to match the values observed by TIRS. The radiative transfer model includes aerosol scattering using a 2-stream approximation (e.g., Smith et al., 2006) and treats absorption by CO2 gas using the correlated-k approximation (Lacis & Oinas, 1991). 1.2 Emirates Mars Mission EMIRS data: EMIRS is a thermal infrared spectrometer that observes Mars at wavelengths between ~100 and 1600 cm-1 (~100 and 6 µm) at a spectral resolution of 5 or 10 cm-1 (Edwards et al., 2021). From its 55-hour period orbit that varies between 20,000 and 43,000 km altitude, EMIRS raster scans the disk of Mars ~20 times during each orbit to provide a global, synoptic view of Mars that samples all local times, both day and night (Amiri et al., 2021). Over the course of approximately 4 orbits (or 10 days), sufficient observations are taken to provide a broad sampling of all local times at nearly all latitudes and longitudes. The typical footprint size is ~100–300 km, which is consistent with modern global circulation models and is sufficient to provide a detailed global view of the current climate state. We follow the constrained linear inversion algorithm of Conrath et al. (2000) and Smith et al. (2006) to retrieve atmospheric state parameters that best match the observed spectra of Mars from EMIRS. The radiative transfer model includes a discrete ordinates treatment of multiple scattering (e.g., Goody & Yung, 1989; Thomas & Stamnes, 1999) to accurately model dust and water ice cloud aerosols, and it accounts for the absorptions from CO2 and water vapor gases using the HITRAN database (Gordon et al., 2022) and the correlated-k approximation (Lacis & Oinas, 1991). Given that the spectral signatures of gases and aerosols are relatively well separated in the spectral range observed by EMIRS, the retrieval is performed sequentially for the atmospheric temperature profile, the column optical depths of dust and water ice aerosol, and the column abundance of water vapor. This sequence can be iterated to obtain a self-consistent solution. 2. Results Figure 1 shows an example of Perseverance/TIRS retrieval of the complex time history of dust optical depth during a regional dust storm that occurred during January 2022. Here, the sol numbers label midnight LTST. During the active period of this dust event between sols 313 and 317 (5–9 January 2022, Ls=153°–156°) there were numerous spikes in aerosol optical depth with several exceeding unity (at 9 µm). These spikes in aerosol (dust) optical depth occurred preferentially during the day but appear equally in both the morning and the afternoon. Retrievals of dust optical depth outside the dust storm period showed a combination of variations on many timescales from very short (minutes), to diurnal, to the overall seasonal trend. Figure 1. The detailed time history of dust optical depth retrieved from Perseverance TIRS observations during the January 2022 regional dust storm. Local variations on short timescales are apparent. The January 2022 regional dust storm was also observed by the Emirates Mars Mission/EMIRS instrument. Figure 2 shows a global-scale view of the initiation, growth, and decay of the storm as observed from orbit. Over the course of several days localized dust activity intensified and spread equatorward becoming a regional storm. New dust lifting quickly diminished and the dust was carried by the general circulation to all longitudes before slowly settling out of the atmosphere. These dust retrievals provide global context to those from the rover. Figure 2. The time history of the global aerosol dust optical depth retrieved from EMIRS observations during the January 2022 regional dust storm. A global view of the evolution of dust is possible from orbit. References Amiri, H.E. S. et al., 2021. Space Sci. Reviews, 218:4, doi:10.1007/s11214-021-00868-x. Conrath, B.J. et al, 2000. J. Geophys. Res., 105, E4, 9509–9519. Edwards, C.S. et al., 2021. Space Sci. Reviews, 217:77, doi:10.1007/s11214-021-00848-1. Goody, R.M. & Yung, Y.L., 1989. Atmospheric Radiation: Theoretical Basis. Oxford Univ. Press. Gordon, I.E., et al., 2022. JQSRT, 277, doi:10.1016/j.jqsrt.2021.107949. Lacis, A.A. & Oinas, V., 1991. J. Geophys. Res., 96, 9027–9063. Rodriguez-Manfredi, J.A. et al., 2021. Space Sci. Reviews, 217:48, doi:10.1007/s11214-021-00816-9. Smith, M.D., et al., 2006. J. Geophys. Res., 111, E12S13, doi:10.1029/2006JE002770. Thomas, G.E. & Stamnes, K., 1999. Radiative Transfer in the Atmosphere and Ocean, Cambridge Univ. Press.

Significance The radiant energy budget is a fundamental metric for planets. Based on the observations from multiple missions, we provide a global picture of Mars’ emitted power. Furthermore, we estimate the radiant energy budget of Mars, which suggests that there are energy imbalances at the time scale of Mars’ seasons. Such energy imbalances provide a new perspective to understanding the generating mechanism of dust storms. Mars’ radiant energy budget is assumed to be balanced at all time scales in current models and theories, but our analyses show that the energy budget is not balanced, at least at the time scale of Mars’ seasons. Therefore, current theories and models should be revisited with the newly revealed energy characteristics.