The Thermal InfraRed Sensor (TIRS) on the Perseverance rover has provided nearly two full Mars years of systematic monitoring of the total aerosol optical depth above Jezero Crater. These observations span a wide range of timescales, capturing seasonal patterns, diurnal variations, and minute-to-minute fluctuations in aerosol loading. By combining TIRS retrievals with orbital observations, the relative contributions of dust and water ice aerosols can be estimated, revealing their different seasonal and diurnal behaviors. The TIRS record shows distinct periods of dust storm activity, including strong regional storms during the perihelion season as well as short-lived but intense dust events outside the typical dust storm season. Water ice clouds exhibit pronounced seasonal and diurnal variability, with peak activity occurring during the aphelion season but with a presence throughout the year. The diurnal variation of clouds differs significantly between the aphelion and perihelion seasons, with clouds persisting throughout the night during the aphelion season, while largely absent outside of specific periods after sunrise and sunset during the perihelion season. These results provide new insights into the complex behavior of aerosols at Jezero Crater and their connections to atmospheric dynamics and the Martian dust and water cycles.

Retrieving the optical depth of the Martian clouds (tau(cld)) is a powerful way to monitor their spatial and temporal evolution. However, such retrievals from nadir imagery rely on several assumptions, including the vertical structure of the clouds in the atmosphere. Here we compare the results of cloud optical depth retrievals at 320 nm from the Emirates eXploration Imager (EXI) onboard the Emirates Mars Mission (EMM) "Hope" orbiter performed using a basic uniform cloud profile used in previous studies and using derived cloud profiles obtained from near-simultaneous Solar Occultation observations in the 3.1-3.4 mu m spectral range from the Middle-Infrared channel of the Atmospheric Chemistry Suite (ACS) instrument onboard the ESA Trace Gas Orbiter (TGO). We show that the latitudinal dependence of the cloud vertical profiles can have a strong impact on the nadir retrievals; neglecting it can lead to a significant underestimation of tau(cld) in the polar regions (up to 25 % to 50 %, depending on the vertical distribution of the dust in the atmosphere) and to a lesser extent, to an overestimation of tau(cld) around the equator. We also discuss the impact of a vertically-dependent particle size profile, as previous studies have shown the presence of very small water ice particles at the top of the clouds. From this analysis, we provide recommendations for the improvement of water ice cloud parameterization in radiative transfer algorithms in nadir atmospheric retrievals.

OMEGA-Py is a Python 3 module dedicated to the scientific use of data provided by the Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument onboard the ESA Mars Express (MEx) orbiter (Bibring et al., 2004).It has been developed as an alternative to the IDL routines (OMEGA Team, 2004) of the OMEGA legacy software provided by the instrument team for the past 20 years.

Introduction: The OMEGA experiment onboard the ESA Mars Express orbiter [1] had observed the Martian surface in the 0.38 – 5.1 µm spectral range from 2004 to 2010. Additional observations with a limited spectral coverage are still ongoing. The dataset contains thousands of hyperspectral cubes covering most of the Martian surface with a typical spatial sampling of 1 km. Repeated observations of the same region have been frequently obtained over the mission, in particular in the high latitudes where time sampling can be about 10° of Ls over most of the year [2]. This spectral range covers water-related spectral signatures of the surface, the most prominent being located at 1.9 and 3 µm [3-6]. Previous studies of the water content derived from the 3 µm band have shown an overall increase of water hydration in the polar regions, with a modeled weight% increased by a factor greater than two in the northern polar latitudes, which presents the highest hydration state levels [5, 6]. The origin of this latitudinal trend is not yet fully understood, although two main hypotheses have been previously suggested and discussed: adsorption of water molecules at the surface (e.g. [5]) and chemical alteration from water molecules deeply bound into minerals or amorphous materials at the surface [6, 7]. We e.g. know that northern polar regions harbor salts, either in the form of large localized deposits of sulfates [8] or at low level in soils [9], as revealed in particular by the in-situ detection of low amount of perchlorates and carbonates from Phoenix [10, 11] not yet identified with orbital observations [12]. In addition, the presence of a significant amount of sub-pixels water ice patches in the polar regions may also result in an average increase of the 3 µm feature when observed at OMEGA resolution. Indeed, recent studies have shown that erosion can create scarps that expose the perennial near-surface water ice contained in the permafrost at latitudes about 55°N [13]. Permafrost depth decreases to a few centimeters at high latitudes while exposed ice stability increases [14], so such subpixels outcrops may be more frequent and could participate to the apparent increase of the 3 µm band depth with latitude. Results: We have conducted a study of the joint variations of the 1.9 and 3 µm bands in the northern polar regions. Figure 1 shows the latitudinal variations of near-IR “albedo” (reflectance factor at 2.5 µm), 1.9 and 3 µm band depths from an OMEGA orbit during the northern summer. To minimize the impact of the well-established dependence of the 3 µm feature on albedo [3, 5, 15], we first focus on a limited albedo range ≥ 0.3. In agreement with previous studies [3,5,6], we observe that the 3 µm band depth continuously increases from 45% to 55% between 50°N and 70°N. We also observe a similar trend for the 1.9 µm band depth that goes from 2% to 4%. Thus, there seems to be a correlation between the latitude dependence of these two bands at global scale. This co-evolution is notably expected in the case of adsorbed water [4]. It may also results from an increase in the amount of trace minerals in soils, like hydrated sulfates that contains a 1.9 µm band, that may be also widespread at polar latitudes [9]. Investigations are ongoing to favor one of these two possible explanations.On the other hand, we can also observe some regional differences of the co-evolution of these two bands, for areas at the same latitude and that presents similar albedo values like in the northern latitudes of Acidalia Planita. Indeed, we can see on figure 2 that at ~ 75°N, there is a darker region between 290°E and 350°E (a). This region is associated with high and stable values of the 1.9 µm band (d). On the other hand, the 3 µm band changes significantly with longitude over the region (c), from 46% at 300°E to 52% at 340°E. The blue and red spectra on figure 2(b) show averaged spectra from two spots in this darker region, and the black spectrum is the ratio between the red (high 3 µm) and the blue (low 3 µm) spectra. We observe with this ratio that there is actually no 1.9 µm band variations between this two spots, whereas variations are notable for the 3 µm band.Conclusion: These first investigations have highlighted the multiplicity of evolution behavior of the 1.9 µm and 3 µm band for different scales. Further work will be dedicated to deeper investigations of the co-evolution of the two bands at a regional scale, and their possible link with other spectral signatures. Our objective is to extend the amount of observational constraints related to the polar increase of the surface hydration observed in the 3 µm spectral range, to bring new constraints about the plausibility of the main two considered hypotheses: adsorbed water versus chemical alteration.Acknowledgments: The OMEGA/MEx data are freely available on the ESA PSA at https://archives.esac.esa.int/psa/#!Table%20View/OMEGA=instrument .References: [1] Bibring et al. (2004) ESA Publication Division, 1240, 37-49. [2] Langevin et al. (2007) JGR, 112, E08S12. [3] Milliken and Mustards (2005) JGR, 110, E12001. [4] Pommerol et al. (2009) Icarus, 204, 114-136. [5] Jouglet et al. (2007) JGR, 112, E08S06. [6] Audourd et al. (2014) JGR Planets, 119, 1969-1989. [7] Beck et al. (2015) EPSL, 427, 104-111. [8] Langevin et al. (2005) Science, 307, 1584-1586. [9] Massé et al. (2012) EPSL, 317-318, 44-55. [10] Boynton et al. (2009) Science, 325, 61-64. [11] Hecht et al. (2009) Science, 325, 64-67. [12] Poulet et al. (2010) Icarus, 205, 712-715. [13] Dundas et al. (2018) Science, 359, 199-201. [14] Smith et al. (2009) Science, 325, 58-61. [15] Pommerol and Schmitt (2008), JGR, 113, E10009.

European Space Agency’s Mars Express (MEX) has been orbiting Mars for 20 years and its instruments have provided a plethora of observations of atmospheric dust and clouds. These observations have been analysed to produce many unique views of the processes leading to dust lifting and cloud formation, and a full picture of the climatologies of dust and clouds has emerged. Moreover, the orbit of MEX enables viewing the planet at many local times, giving a unique access to the diurnal variations of the atmosphere. This article provides an overview of the observations of dust and clouds on Mars by MEX, complemented by the Trace Gas Orbiter that has been accompanying MEX on orbit for some years.

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.

Introduction. Visible and near-infrared observations of Mars have revealed a wide range of primary and secondary alteration minerals. Hydrated minerals were first identified from orbit with the Observatoire pour la Minéralogie, l’Eau, les Glaces, et l’Activité (OMEGA) instrument. OMEGA data were used to produce global maps of aqueous minerals [1], including the polar regions [5], in particular the northern one [2]. Recently, the Mars Orbital Catalog of Aqueous Alteration Signatures project [3] including OMEGA observations and data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) produced a set of the more accurate and resolved maps of aqueous minerals at latitudes ranging from 70°S to 70°N. However, no recent systematic study of the distribution and nature of the aqueous composition has been carried out in the south polar regions. OMEGA observations highlighted spectral variability of the Martian high latitude surfaces [5, 4]. In particular, the 1.9 µm and 3 µm band depths increase from 60° latitudes towards the poles [1, 5], which suggests that hydrated minerals may participate in this spectral variability. [4] indeed reported the detection of a deep and relatively narrow absorption band at 3 µm coupled with a shallow but significantly wider 4 µm feature in the northern high latitudes of Mars. This feature may be related to sulfates and has no significant counterpart in the south for now. Moreover, the 1.9 µm band is significantly broader and shifts to slightly longer wavelengths in the south polar region which seems to indicate a specific mineralogy, and/or a different hydration state from that of the north [5]. Here we present a spectral analysis and the detection of hydrated minerals in the south polar region.Method. OMEGA has been observing the Martian surface since 2004 between 0.35 and 5.1 µm. Here, we selected observations acquired during southern spring and summer as high latitudes are covered by seasonal ice during winter. OMEGA data have been processed using the OMEGA-Py Python module [8]. Our analyses focus on the detection and characterization of hydrated minerals using several spectral criteria previously defined: the band depths (BD) at 1.9 µm [4], 2.1 µm [6] and 2.4 µm [4]; the narrow and wide 3 µm band depths [4] and the SINDEX [6]. We have developed a new estimator adapted to the broader and shifted 1.9 band observed in the southern high latitudes, called here the “wide 2 µm band depth (WBD)”. This criterion estimates the band depth centered at 2 µm using the average continuum from 1.75 to 1.85 µm and 2.20 to 2.30 µm. Since the 3 µm band is very sensitive to the presence of water ice at the surface or in the atmosphere [7], we remove pixels with a water ice absorption at 1.5 µm>1%. In order to prevent possible effects related to viewing geometry, we removed pixels with emergence and incidence angles respectively higher than 10° and 75°. We then isolate detections of sulfate-bearing units thanks to a combination of four of these spectral criteria: the BD at 1.9, 2.1 and 2.4 µm and the SINDEX.Results. The spatial distribution of all the spectral criteria over the whole OMEGA dataset in the south polar region have been investigated. All the criteria exhibit a strong variability in this region. The narrow 3 μm BD identified for the first time by [4] in the north polar region shows a different behavior in the south polar region. This spectral parameter varies mainly from 0 to 10% in the southern polar region while it increases to more than 30% in the northern polar region. The WBD at 2 µm is present at all longitudes between 50°S and 90°S and varies from 1% to 6% (Fig 1). The wide 3 μm BD is almost always higher than 35% and increases over 65% in this region. The WBD at 2 µm and the WBD at 3 µm increase with latitude toward the south pole (Fig 1). In addition to latitudinal variations, the WBD at 2 µm exhibits seasonal variations and decreases over the summer. The map of hydrated minerals detections in the south polar region (Fig 2) shows a high concentration of sulfate-bearing units around the polar cap. High-resolution CRISM observations obtained over this unit confirm that the spectral signatures can be confidently attributed to sulfates.Perspectives. The spectral signatures between the sulfate detections presented here and the sulfates in Meridiani Planum are different especially around 3 μm which may indicate different sulfates compositions and/or different mixings with other minerals. Such differences may provide clues about the specific sulfates formation and transformation pathways expected at high latitudes. The ring-like structure of the south polar sulfates suggest a formation associated with seasonal frost and/or polar ice cap. The absence of the narrow 3 μm band depth around the south pole differentiate the two Martian poles in term of spectral variations. Further study of the spectral signatures and comparison with geological maps is in progress, and will help constrain the scenario for the formation of these hydrated minerals in the South Polar region.References[1] Poulet et al., (2007). JGR: Planets, 112(E8). [2] Langevin et al., (2005). Science, 307, 5715. [3] Carter et al., (2023). Icarus, 389, 115164. [4] Stcherbinine et al., Icarus, 369, 114627 (2021). [5] Poulet et al., GRL, 35(20) (2008). [6] Viviano-Beck et al., JGR:Planets, 119(6), 1403-1431(2014). [7] Jouglet et al., JGR:Planets 112.E8 (2007). [8] Stcherbinine (2023). Zenodo, doi:10.5281/zenodo.10035061 Figure 1: Composite maps of 833 OMEGA observations in the south polar region of Mars. Solar longitude of the observations ranges from 260° to 340°, corresponding to late southern spring and southern summer. Color codes shows the spectral variations of the wide 2 µm band depth (left) and the wide 3 µm band depth (right).Figure 2: Map of hydrated mineral detections in the south polar region of Mars (50°S-90°S). Pixels in blue represents monohydrated sulfates detection, in green polyhydrated sulfates detection and pixels in red are phyllosilicates detection. Based map is the wide 3 µm band depth.

Clouds play a crucial role in the past and current climate of Mars. Cloud particles impact the planet's energy balance and atmospheric dynamics, as well as influence the vertical distribution of dust particles through dust scavenging. This process of dust scavenging by clouds has significant consequences for the planet's water cycle. For example, regions in the atmosphere with insufficient quantities of dust particles, or condensation nuclei, can inhibit the formation of H2O clouds, leading to the presence of water vapor in excess of saturation [1]. Recent observations made by the MEDA Radiation and Dust Sensor (RDS) [2,3] have shown a marked decline in mesospheric cloud activity (above 35-40 km) when Mars is near its aphelion (within the Aphelion Cloud Belt-ACB season), notably occurring during solar longitudes (Ls) between Ls 70° and 80° [4] (see Figure 1).In order to investigate the possible factors leading to this decrease in water ice abundance, we used a one-dimensional cloud microphysical model [5,6], which includes the processes of nucleation, condensation, coagulation, evaporation, precipitation, and coalescence, and where the vertical mixing is parameterized using an eddy diffusion profile (Keddy). Combining cloud microphysics modeling with ground-based (Mars 2020 and InSight) and orbital observations (TGO and MRO) of clouds, water vapor, and temperature, we will discuss in this presentation the main factors controlling the water abundance in the Martian mesosphere during the ACB season.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, V., et al. “Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover”. Sensor 22.8 (2022): 2907. [3] Rodriguez-Manfredi, Jose Antonio, et al. “The Mars Enviromental Dynamics Analyzer, MEDA. Asuite of enviromental 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. [5] Montmessin, F., Rannou, P., Cabane, M.: New insights into martian dust distribution and water-ice cloud microphysics. Journal of Geophysical Research: Planets 107(E6), 41 (2002). [6] Rannou, P., Montmessin, F., Hourdin, F., Lebonnois, S.: The latitudinal distribution of clouds on titan. science 311(5758), 201205 (2006).

MIRS (MMX InfraRed Spectrometer) is the imaging spectrometer (0.9-3.6 µm) [1] of the JAXA MMX (Martian Moon eXploration) mission [2]. The mission will be launched in the autumn 2026 to the Martian system, with an arrival around Mars planned in autumn 2027. The main objective of the mission is to study the two Martian moons, Phobos and Deimos, to collect samples of Phobos and bring them back to Earth in 2031. Another major objective of the mission [3] and the MIRS instrument [1] is to answer key science questions regarding the transport processes of dust and water in the Martian atmosphere [3], such as: how do local and regional dust storms form, grow and evolve? What is the diurnal behaviour of water ice clouds (formation, transport, dynamics)? The MMX probe will be injected into a quasi-circular equatorial orbit around Mars at an altitude of about 6000 km from the surface. From this particular orbit, three different observation modes of MIRS are expected for Mars observations (see Figure 1) in addition to the limb mode: the so-called nominal mode whose purpose is to monitor up to low-medium latitudes, global mapping mode that covers most of the lighted Martian disk up to high latitudes (± 60°), and region of interest mode that provides temporal resolution (down to 15 minutes) above a chosen area. Each mode will be used to study the spatial and temporal variations of the aerosols (atmospheric dust, water and CO2 ice), and their fine diurnal variations. Indeed, the particular orbit of MMX (the second probe after Hope from EMM [4] to be in equatorial orbit) will allow MIRS to provide high-resolution spectral images in near-infrared and at very different local times, which will certainly contribute to answer to the questions addressed above. Figure 1: Illustration of the three expected observation modes of MIRS in addition to the limb mode: [A] nominal mode, [B] global mapping mode and [C] region of interest mode. Credits: CNES. The retrieval pipeline for the MIRS observations is being prepared in coordination between the instrument team and the Mars Sub Science Team of the MMX mission. The two retrieval modules for trace gas and aerosols with nadir and limb observations are currently under development and will be validated by testing them on existing OMEGA/Mars Express data (e.g., [5], [6], [7]). In this study, focused on the aerosol retrievals, we use the DISORT (DIScrete-Ordinate-method Radiative Transfer) code [8, 9] through the pyRT_DISORT Python module [10] to simulate the expected radiance of the Martian atmosphere that MIRS will measure. First, we will present the parameter space exploration (estimated at up to 10 dimensions) of the radiative transfer model done to quantify the impact of each physical parameter (e.g., observation angles, surface albedo) on the generated spectra. Then, we will discuss the look-up table created by using different algorithms to explore the parameter space and their sampling in order to optimise the size of the look-up table (estimated at almost 75 million spectra), the computation time to create it, and to search in it. This table will be used to retrieve the aerosol properties in the flight data, which allows a faster retrieval than spectrum-to-spectrum inversion (given the large quantity of data that will be returned by MIRS). Finally, we will present MIRS images simulated with DISORT in real conditions during Phase 0 (orbit insertion and phasing), corresponding to the arrival of the MMX probe around Mars in 2027, for the different MIRS observation modes. These simulated data will be used to test the retrievals with the look-up table for future observations of Mars, get an understanding of the reachable performances, and help in defining the Phase 0 Mars set of observations.Acknowledgments:We thank the MMX JAXA teams for their efforts and CNES for the financial support and collaboration to build the MIRS instrument.References:[1] Barucci M. A. et al. (2021) Earth, Plan. and Space, 73, 211. [2] Kuramoto K. et al. (2022) Earth, Plan. and Space, 74, 12. [3] Ogohara K. et al. (2021) Earth, Plan. and Space, 74, 1. [4] Amiri H. E. S. et al. (2022) Space Sciences Reviews, 218:4. [5] Nakagawa H. et al. (2022) Seventh International Workshop on the Mars Atmosphere: Modelling and Observations, id3562. [6] Aoki S. et al. (2024), Japan Geoscience Union Meeting 2024. [7] Kazama A. et al. (2024), The Tenth International Conference on Mars. [8] Connour K. & Wolff M. (2023) GitHub repository, pyRT_DISORT. [9] Stammes K. et al. (1988) Applied Optics, 27, 2502-2509. [10] Stammes K. et al. (2017) Astrophys. Source Code Library, 1708.006.

Montabone et al., 2015 and 2020, [1, 2] have developed an iterative, weighted, running mean methodology to grid the available retrievals of atmospheric column dust optical depth (CDOD) from multi-annual and multi-instrument spacecraft observations at Mars. The application of this methodology has produced daily gridded maps of CDOD from Martian Year (MY) 24 through 35, using Mars Global Surveyor/Thermal Emission Spectrometer and Mars Odyssey/Thermal Emission Imaging System nadir observations, as well as the estimates of this quantity from Mars Reconnaissance Orbiter/Mars Climate sounder (MRO/MCS) limb observations. Given the lack of dust observations at certain times and locations, the daily gridded maps have missing values at some grid points. Kriging spatial interpolation has been used to produce regular maps that are useful as multiannual dust scenarios for model simulations, and for the Mars Climate Database (MCD) statistics [3].We have now adapted this methodology to include CDOD retrievals from Emirates Mars Mission/Emirates Mars Infrared Spectrometer (EMM/EMIRS) nadir observations in MY 36 [4]. The specificity of EMIRS spatial and temporal coverage as well as the extended nature of its footprint are taken into account when carrying out the gridding. We will present a cross-comparison of maps obtained using only EMIRS retrievals and maps obtained using only MCS retrievals, in the attempt to understand what is the best approach to produce a MY 36 dust scenario that makes the best use of both instruments. We will particularly focus on the evolution of large-scale dust storms in MY 36.References: [1] Montabone, L., et al. (2015) Icarus 251, pp. 65-95, doi: 10.1016/j.icarus.2014.12.034 ; [2] Montabone, L., et al. (2020) J. Geophys. Res. - Planets, doi: 10.1029/2019JE006111 ; [3] http://www-mars.lmd.jussieu.fr (Publicly available dust gridded maps can be currently found up to MY 35 by clicking on the “climatologies of Martian atmospheric dust” link under “Martian dust Climatology”) ; [4] Smith, M.D., et al. (2022) Geophys. Res. Lett. 49, Issue 15, doi: 10.1029/2022GL09963

Condensation and sublimation of ices at the surface of the planet is a key part of both the Martian H2O and CO2 cycles, either from a seasonal or diurnal aspect. While most of the ice is located within the polar caps, surface frost is known to be formed during nighttime down to equatorial latitudes. Here, we use data from the Emirates Mars Infrared Spectrometer onboard the Emirates Mars Mission to monitor the diurnal and seasonal evolution of the ices at the surface of Mars over almost one Martian year. The unique local time coverage provided by the instrument allows us to observe the apparition of equatorial CO2 frost in the second half of the Martian night around the equinoxes, to its sublimation at sunrise.

<p>Observations of clouds in planetary atmospheres can provide insight about atmospheric characteristics such as vertical temperature structure and dynamics. Clouds observed at the limb of a planet (from the perspective of the telescope or spacecraft observing them) can be particularly useful tools, in part because their height above the surface can be measured directly.</p> <p>The Emirates Mars Mission (EMM) has been recording visible light images of the Martian disk since early 2021, using the Emirates eXploration Imager (EXI). We present an analysis of limb clouds evident in EXI images taken using its red filter (centered on 635 nm) over the course of a Martian year. We present statistics on their height, thickness, spatial extent, and geographic and local time distribution – as well as correlations between these parameters. We place our results in context with previous work, and explore reasons for observed trends.</p>

Introduction Observations from OMEGA, the visible-near infrared hyperspectral imager onboard the Mars Express orbiter, highlighted spectral variability of the Martian high latitude surfaces [1]. In particular, the 1.9 µm and 3 µm band depths increase from 60° latitudes towards the poles [1, 2, 3], which suggests that hydrated minerals may participate in this spectral variability. [3] reported the detection of a deep and relatively narrow absorption band at 3 µm coupled with a shallow but significantly wider 4 µm feature in the northern high latitudes of Mars, with no significant counterpart in the south for now. Comparison with laboratory spectra suggest that these features may be associated with the presence of salts such as sulfates and/or perchlorates [3]. In the south polar region, several absorption features related to water-bearing minerals (e.g., sulfates, phyllosilicates) have been identified in the 1 – 2.6 µm spectral range [1, 4]. As a result, sulfate salts were mapped over large areas there, but their precise mineralogy and distribution is not constrained [4]. Moreover, the 1.9 µm band is significantly broader and shifts to slightly longer wavelengths in the south which seems to indicate a specific mineralogy, and/or a different hydration state from that of the north [1]. Here we present the preliminary results of a study about the combined evolution of the spectral features identified in the southern high latitudes. Method The OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces, et l’Activité) instrument has been observing the surface of Mars since 2004 between 0.35 and 5.1 µm. Here, we selected observations acquired during southern spring and summer as high latitudes are covered by seasonal ice during winter. Our analyses focus on the detection and characterization of hydrated minerals, in particular sulfates, using several spectral criteria previously defined: the band depths at 1.9 µm [5], 2.1 µm [6] and 2.4 µm [3]; the narrow [3] and wide 3 µm band depths [2]. We have also developed a new estimator for the wide band depth observed around 2 µm in the south polar region [1]: where is the average reflectance from the n spectels corresponding to wavelengths (µm). Since the 3 µm band is very sensitive to the presence of water ice at the surface or in the atmosphere [7], we remove pixels with a water ice absorption at 1.5 µm>1%. In order to prevent possible effects related to viewing geometry, we removed pixels with emergence and incidence angles respectively higher than 10° and 75°. Preliminary results The parameters exhibit a strong variability in the south polar region (Figure 1 and 3) which suggest possible variations of the hydration state and/or mineralogical composition of the surface. As already demonstrated, the 1.9 µm and the wide 3 µm band depths increase towards the pole (Figure 2 and 3). The intensity of the “narrow 3 µm band” criteria such as defined by [3] is significantly (two times) lower than in the north polar region. The wide band depth around 2 µm is higher than 3% in the whole area and increases up to 5% at 75°S. Beside this regional spectral variability, we can also notice localized area which may have a specific spectral pattern, e.g., near 58°S where the 3 µm band shape is modified in such a way that the wide band depth criteria is reduced while the narrow one increases; at the same time the 2.4 µm band is reduced while the wide 2 µm criteria increases (Figure 2 and 3). Although not following as clear a latitudinal trend, we find large areas of hydrated sulfate salt signatures through a combination of the 1.9 µm band and 2.4-2.5 µm spectral shoulder. These occur preferentially at high southern latitudes. Perspectives Preliminary results show a large range of diversity in the near-infrared between 1.4 and 2.6 µm but also around 3 µm (Figure 1). The band depths at 1.9 and 3 µm are strong indicators of the surface hydratation [2] and bands in the 1.9 - 2.1 and 2.4 µm ranges may be associated with sulfates [4, 8]. By using these band depths and additional spectral criteria, we plan to estimate the coverage and properties of hydrated minerals, in particular sulfates, in the south polar region, following previous studies by [1] and [4]. We also plan independent validation and further characterization of the mineralogy of some of these areas using CRISM high-resolution observations. This reappraisal of available spectral constraints compared with the geomorphological context will improve our understanding of the formation scenarios of the hydrated minerals, in particular sulfates, in the south polar region of Mars. Figure 1: NIR-1 µm Albedo map [9] of the region where the OMEGA cube ORB2209_3 is located (latitude ranges between -53°N to -78°N and longitude between 131°E to 145°E). Figure 2: Latitudinal variations of the spectral parameters in the OMEGA cube ORB2209_3 (Figure 1). Figure 3: Variability of the spectral parameters in the OMEGA cube ORB2209_3 between -53°N to -65°N, from left to right: band depth at 1.9 µm, narrow and wide band depth at 3 µm and 2 µm. Data availability The OMEGA/MEx data are freely available on the ESA PSA at https://archives.esac.esa.int/psa/#!Table%20View/OMEGA=instrument. This work uses the OMEGA-Py Python module, freely available on GitHub at https://github.com/AStcherbinine/omegapy. References [1] Poulet et al., GRL, 35(20) (2008). [2] Jouglet et al., JGR:Planets 112.E8 (2007). [3] Stcherbinine et al., Icarus, 369, 114627 (2021). [4] Carter et al., Sixth International Conference on Mars Polar Science and Exploration (Vol. 1926, p. 6063) (2016). [5] Langevin et al., Science, 307, 5715 (2005). [6] Viviano-Beck et al., JGR:Planets, 119(6), 1403-1431(2014). [7] Vincendon et al., JGR:Planets 116.E11 (2011). [8] Gendrin et al., Science, 307, 5715, 1587-1591 (2005). [9] Ody et al., JGR:Planets, 117(E11), (2012)

The middle infrared (MIR) channel of the atmospheric chemistry suite (ACS) instrument onboard the ExoMars Trace Gas Orbiter ESA‐Roscosmos mission has performed Solar occultation measurements of the Martian atmosphere in the 2.3–4.2 μm spectral range since March 2018, which now covers two Martian years (MY). We use the methodology previously developed for the study of the MY 34 global dust storm (GDS) (Stcherbinine et al., 2020, https://doi.org/10.1029/2019je006300) to monitor the properties (effective radii, extinction, and altitude) of the Martian water ice clouds over the first two Martian years covered by ACS‐MIR. The observations encompass the period Ls = 163° in MY 34 to Ls = 181° in MY 36. We determine that the typical altitude of the clouds varies by 20–40 km between the summer and winter, with a maximum extension up to 80 km during summer in the midlatitudes. Similarly, we also note that for a limited temporal range, the altitude of the clouds also varies by 20–40 km between the polar regions and the midlatitudes. We also compare observations acquired during the MY 34 GDS to observations from the same period in MY 35, using the latter as a reference to characterize the effects of this GDS on the clouds' properties. In addition, we compare our retrievals with the predictions of the Mars planetary climate model, which shows a reasonable agreement overall for the altitude of the clouds, although the model usually predicts lower altitudes for the top of the clouds.

The Atmospheric Chemistry Suite (ACS) MIR channel onboard the ESA-Roscosmos Trace Gas Orbiter (TGO) (Korablev et al., 2018, 2019) probes the Martian atmosphere in the 2.3 – 4.2 µm spectral range using the Solar Occultation technique. ACS-MIR has now provided infrared observations of the Martian atmosphere over more than one and a half regular Martian Year since the end of the 2018/MY34 Global Dust Storm (GDS).We analyzed this ACS-MIR dataset to detect the presence of water ice particles in the Martian atmosphere and retrieve their size from the 3 μm atmospheric absorption signature. Each observation results in a vertical profile of ice particle size within the cloud layer, with a vertical resolution of a few kilometers. The temporal and spatial sampling provided by the 2-hour period of TGO’s orbit allows us to observe the seasonal and latitudinal trends of the water ice clouds, with variations of about 20 to 40 km of the cloud’s altitude.The method was first applied solely to the 2018/MY34 GDS year (Stcherbinine et al., 2020). This first study notably revealed the presence of small-grained clouds at very high altitudes (above 100 km) at the onset of the MY34 GDS, along with the presence of large water ice particles (reff > 1.5 µm) up to 65 km during the storm.Data acquired during MY35, where no GDS occurred, provides a reference to be compared with the observations obtained during the MY34 GDS. We observe that the maximum altitude of the water ice clouds increases by about 10 km during the GDS compared to a nominal year, which suggests that the GDS significantly impacts water ice cloud distribution.

Mars northern polar latitudes are known to harbor an enhanced 3 μm spectral signature when observed from orbit. This may indicate a greater amount of surface adsorbed or bound water, although it has not yet been possible to easily reconcile orbital observations with ground measurements by Phoenix. Here we reprocessed OMEGA/Mars Express observations acquired during the Northern summer to further characterize this 3 μm absorption band increase. We identify the presence of a new specific spectral signature composed of an additional narrow absorption feature centered at 3.03 μm coupled with an absorption at ≥ 3.8 μm. This signature is homogeneously distributed over a bright albedo open ring surrounding the circumpolar low-albedo terrains between ∼ 68◦N and 76◦N and ∼ 0◦E and 270◦E. This location includes the Phoenix landing site. This feature shows no time variability and can be confidently attributed to a seasonally stable surface component. All together, the stability, spectral shape and absence of significant correlation with other signatures in the 1 – 2.5 μm range discard interpretations relying onwater ice or easily exchangeable adsorbedwater. The exact full spectral shape cannot be easily reproduced by pure minerals samples, although sulfates, notably lowly hydrated Ca-sulfates, provide interesting comparisons. A modification of the chemical or physical properties of the soil, potentially involving additional sulfates contaminants, or modification of the hydration state of sulfates, and/or modification of their grains size, seems a plausible explanation to this observation, which may then indicate geologically recent water alteration at high northern latitudes.

Introduction: Dust is omnipresent within Mars’s atmosphere [1] and at its surface [2]. These small, micrometer-sized particles are one of the major features of Mars modern climate [3] and may also represent a key factor controlling some current surface properties such as composition [4] and activity [5]. Multiple orbital and surface observations have already revealed the main features of the dust seasonal cycle (e.g. [1, 3]). However, some characteristics are still imperfectly known, such as the different lifting mechanisms, the preferential locations where dust settles down, and the driving forces of Global Dust Storms (GDS). Recently, it has been suggested that Recurring Slope Lineae (RSL) [6] may be primarily connected to the dust cycle [5, 7]. Our work aims at better understanding where, when and how dust moves on Mars. This may help understanding how the different spatial scales, from global dust storm to local phenomena such as RSL, are connected. We start with the development of a new method to identify local dust storms in Mars Express observations. Data and method: We use the 1 to 2.5 μm “Cchannel” (and “L-channel”: 2.55-5.1 μm for spectral criteria) of OMEGA [8], an imaging spectrometer that has observed the surface with a typical spatial sampling of 1 km over three Martian years (2004-2010). We have developed a new method to detect the presence of dust in the atmosphere in this dataset. This method is based on the 2 μm carbon dioxide (CO2) absorption band. When the atmosphere is “clear” (without dust or cloud), photons travel a given distance in the atmosphere. This distance through CO2 is reduced if an aerosols layer is present. If we are able to predict the expected CO2 path without atmospheric dust, then it should be possible to detect anomalously weak CO2 path length resulting from the presence of dust or clouds in the atmosphere. We first developed a basic physical model to link the CO2 optical depth without dust to pressure, surface albedo and solar incidence angle. Pressure is the main parameter: it characterises the amount of CO2 in the atmosphere as a function of geographical position and season. It is extracted from a climate model [9]. Solar incidence angle controls the geometry of photons’ path as viewing geometry is nadir. Surface albedo modifies the proportion of photons measured by the instrument after surface contact. This model has been calibrated using observations without dust. Observations have been selected inside typical clear atmospheric periods/locations according to previous TES observations [10]. We paid a particular attention on filtering water ice both as clouds and at the surface, using spectral criteria at 1.5 microns and 3.5 microns [11, 12]. Indeed, water ice is a potential aerosols contributor and it has also a large absorption band around 2 μm.

WATER BAND OBSERVED BY OMEGA. A. Stcherbinine, M. Vincendon, F. Montmessin and P. Beck Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, Orsay, France, LATMOS, UVSQ, Université Paris-Saclay, CNRS, Sorbonne Université, Guyancourt, France, Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble Alpes, CNRS, Saint-Martin d’Heres, France. (aurelien.stcherbinine@ias.u-psud.fr)