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On 21st April 2018, the ExoMars Trace Gas Orbiter began its nominal science phase [1]. Since then, for the last 6 and a half years, the NOMAD instrument has taken more than a 100 million spectra in the ultra-violet, visible and infrared.NOMAD, or "Nadir and Occultation for MArs Discovery", is a suite of three spectrometers: two operate in the infrared and one operates in the 200-650nm range. Of the two infrared spectrometers, "SO" is designed primarily for solar occultation observations; and "LNO" is primarily designed for nadir observations but can also operate in solar occultation and limb modes [2], and measure Phobos. The ultraviolet-visible spectrometer can do all the above: solar occultation, limb, nadir, and Phobos and Deimos observations [3].The very high resolving power of the infrared SO and LNO spectrometers (~17000 and ~10000 respectively [4]) mean that they are well suited for measuring atmospheric absorption lines, and are therefore able to measure clouds [5], dust [6], H2O [7], [8], CO [9], [10], CO2 (for temperature and pressure)[11], [12] and HCl [13] in solar occultation mode, plus their isotopes such as HDO [14] and H37CL [15]. SO spectra can also be used to put upper limits on trace gases that are not detected, such as CH4 [16] and HF. In nadir, LNO is primarily measuring H2O [17] and CO [18] in the atmosphere and the albedo/composition of the surface [19], [20]. Work is being done the constrain the potential 2.7µm hydration band in Phobos spectra.The ultraviolet-visible spectrometer, "UVIS", measures O3 and dust/aerosols in both solar occultation [21] and nadir modes [22], in addition to Phobos and Deimos [23]. Of particular note is the ongoing work to observe the limb of Mars during both the day and night, to measure the various airglow emission lines present in the limb spectra [24], [25], [26], [27].Also, calibration efforts are continually ongoing to improve detection limits and retrieval accuracies.In this presentation we will show the latest results from NOMAD, and describe how scientists outside the NOMAD team can also access all the latest data generated by the instrument. References[1] A. C. Vandaele et al., `Science objectives and performances of NOMAD', PSS, 2015, doi: 10.1016/j.pss.2015.10.003.[2] E. Neefs et al., `NOMAD spectrometer on the ExoMars trace gas orbiter mission: part 1—design, manufacturing and testing of the infrared channels', Appl. Opt., 2015, doi: 10.1364/AO.54.008494.[3] M. R. Patel et al., `NOMAD spectrometer on the ExoMars trace gas orbiter mission: part 2—design, manufacturing, and testing of the ultraviolet and visible channel', Appl. Opt., 2017, doi: 10.1364/AO.56.002771.[4] G. Liuzzi et al., `Methane on Mars: New insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration', Icarus, 2019, doi: 10.1016/j.icarus.2018.09.021.[5] G. Liuzzi et al., `First Detection and Thermal Characterization of Terminator CO 2 Ice Clouds With ExoMars/NOMAD', GRL, 2021, doi: 10.1029/2021GL095895.[6] A. Stolzenbach et al., `Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements', JGR Planets, 2023, doi: 10.1029/2022JE007276.[7] S. Aoki et al., `Global Vertical Distribution of Water Vapor on Mars: Results From 3.5 Years of ExoMars-TGO/NOMAD Science Operations', JGR Planets, 2022, doi: 10.1029/2022JE007231.[8] A. Brines et al., `Water Vapor Vertical Distribution on Mars During Perihelion Season of MY 34 and MY 35 With ExoMars-TGO/NOMAD Observations', JGR Planets, 2023, doi: 10.1029/2022JE007273.[9] N. Yoshida et al., `Variations in Vertical CO/CO 2 Profiles in the Martian Mesosphere and Lower Thermosphere Measured by the ExoMars TGO/NOMAD: Implications of Variations in Eddy Diffusion Coefficient', GRL, 2022, doi: 10.1029/2022GL098485.[10] A. Modak et al., `Retrieval of Martian Atmospheric CO Vertical Profiles From NOMAD Observations During the First Year of TGO Operations', JGR Planets, 2023, doi: 10.1029/2022JE007282.[11] M. A. López-Valverde et al., `Martian Atmospheric Temperature and Density Profiles During the First Year of NOMAD/TGO Solar Occultation Measurements', JGR Planets, 2023, doi: 10.1029/2022JE007278.[12] L. Trompet et al., `Carbon Dioxide Retrievals From NOMAD-SO on ESA's ExoMars Trace Gas Orbiter and Temperature Profile Retrievals With the Hydrostatic Equilibrium Equation', JGR Planets, 2023, doi: 10.1029/2022JE007279.[13] S. Aoki et al., `Annual Appearance of Hydrogen Chloride on Mars and a Striking Similarity With the Water Vapor Vertical Distribution Observed by TGO/NOMAD', GRL, 2021, doi: 10.1029/2021GL092506.[14] G. L. Villanueva et al., `The Deuterium Isotopic Ratio of Water Released From the Martian Caps as Measured With TGO/NOMAD', GRL, 2022, doi: 10.1029/2022GL098161.[15] G. Liuzzi et al., `Probing the Atmospheric Cl Isotopic Ratio on Mars: Implications for Planetary Evolution and Atmospheric Chemistry', GRL, 2021, doi: 10.1029/2021GL092650.[16] E. W. Knutsen et al., `Comprehensive investigation of Mars methane and organics with ExoMars/NOMAD', Icarus, 2021, doi: 10.1016/j.icarus.2020.114266.[17] M. M. J. Crismani et al., `A Global and Seasonal Perspective of Martian Water Vapor From ExoMars/NOMAD', JGR Planets, 2021, doi: 10.1029/2021JE006878.[18] M. D. Smith et al., `The climatology of carbon monoxide on Mars as observed by NOMAD nadir-geometry observations', Icarus, 2021, doi: 10.1016/j.icarus.2021.114404.[19] L. Ruiz Lozano et al., `Observation of the Southern Polar cap during MY34-36 with ExoMars-TGO NOMAD LNO', Icarus, 2024, doi: 10.1016/j.icarus.2023.115698.[20] F. Oliva et al., `Martian CO2 Ice Observation at High Spectral Resolution With ExoMars/TGO NOMAD', JGR Planets, 2022, doi: 10.1029/2021JE007083.[21] M. R. Patel et al., `ExoMars TGO/NOMAD-UVIS Vertical Profiles of Ozone: 1. Seasonal Variation and Comparison to Water', JGR Planets, 2021, doi: 10.1029/2021JE006837.[22] J. P. Mason et al., `Climatology and Diurnal Variation of Ozone Column Abundances for 2.5 Mars Years as Measured by the NOMAD-UVIS Spectrometer', JGR Planets, 2024, doi: 10.1029/2023JE008270.[23] J. P. Mason et al., `Ultraviolet and Visible Reflectance Spectra of Phobos and Deimos as Measured by the ExoMars-TGO/NOMAD-UVIS Spectrometer', JGR Planets, 2023, doi: 10.1029/2023JE008002.[24] J.-C. Gérard et al., `Detection of green line emission in the dayside atmosphere of Mars from NOMAD-TGO observations', Nat Astron, 2020, doi: 10.1038/s41550-020-1123-2.[25] J.-C. Gérard et al., `First Observation of the Oxygen 630 nm Emission in the Martian Dayglow', GRL, 2021, doi: 10.1029/2020GL092334.[26] J.-C. Gérard et al., `Observation of the Mars O2 visible nightglow by the NOMAD spectrometer onboard the Trace Gas Orbiter', Nat Astron, 2024, doi: 10.1038/s41550-023-02104-8.[27] L. Soret et al., `The Ultraviolet Martian Dayglow Observed With NOMAD/UVIS on ExoMars Trace Gas Orbiter', JGR Planets, 2023, doi: 10.1029/2023JE007762.

Aerosols are an important part of the Martian atmosphere. They are composed of dust, H2O ice, and CO2 ice. Dust is the main aerosol and has a significant contribution to the radiative transfer budget, as it absorbs solar radiation, leading to local heating of the atmosphere. Dust is confined to lower altitudes during the aphelion season and can reach higher altitudes during the perihelion, especially during dust storms that frequently arise on Mars during this period. The seasonal behavior of the dust will lead to temperature variations in the atmosphere that are important, especially for modelers. Ice clouds are more present during the aphelion when the temperature is colder and follow a seasonal pattern. Different types of clouds can be found throughout the year and contrary to dust, they reflect sunlight and locally cool the atmosphere.The thermal and dynamical structure of the atmosphere, as well as the distribution of chemical species are sensitive to the aerosol's abundance and size.The NOMAD ("Nadir and Occultation for MArs Discovery") spectrometer suite onboard the ExoMars Trace Gas Orbiter (TGO) is composed of three spectrometers. In this work, we will use the UVIS and SO channels in occultation mode. Both channels are respectively in the UV-Visible (200-650 nm) and infrared (2.3-4.3 µm).We first developed a methodology to compute extinction and particle sizes with the UVIS channel. The climatology produced allowed us to study aerosols along different seasons and latitudes between the second half of Martian Year (MY) 34 up to the end of MY 36 (figure 1).Using only the spectral range of UVIS in occultation, dust, H2O ice, and CO2 ice cannot be differentiated because the three aerosols have similar extinction features. To model the extinction cross-section, we assume spherical symmetry and use a Mie scattering code (Bohren, et al., 1998). We use the commonly used log-normal size distribution with the parameterization of (Hansen, et al., 1974).We show that with UVIS it is possible to distinguish size between 0.1 to 0.8 µm with confidence. When the particles are larger, it is not possible to retrieve the precise size, as the spectra does not possess any absorption bands.With the addition of the infrared channel, NOMAD SO, we can broaden the sensitivity with respect to particle size and can retrieve the composition of the aerosols. H2O ice, CO2 ice, and dust possess different signatures in the IR (figure 2) and it is possible to differentiate them with confidence. The combination of both UVIS and SO greatly improves the retrieval of particle size as it allows us to have more sensitivity for larger particles.Several works have already published climatologies of aerosols with NOMAD. Liuzzi et al., (2019) study water ice cloud and dust particles with the SO channel during MY34 and the beginning of Martian year 35.They were able to discriminate the aerosols and study the presence and evolution of water ice clouds during dust storms. Stolzenbach et al., (2023) also made a similar study , also using SO, from MY 34 to MY 35. Both works were able to study in detail the size distribution during dust events.Streeter et al (2022), used the UVIS channel to produce a climatology of aerosols between MY34 to the end of MY35. They derived extinction vertical profiles but not the size of the particles. Using a model, they were also able to study the presence of water ice clouds and dust in the atmosphere.By the combination of previous work's results, and the methodology developed for the UVIS channel, we aim to create a new climatology covering from MY34 to the end of MY 36. This new data set will use information contained in the UV and IR channels allowing us to have greater constraints on size and composition of the aerosols. We will be able to study in detail the evolution and occurrence of detached layers during several seasons and latitudes. Figure 1: Extinction vertical profiles with the UVIS channel as a function of LS for the northern ([30°,70°] Lat, Top panel), equatorial ([-30°,30°] Lat, Middle panel), and southern latitude ([-70°,-30°] Lat, Bottom panel) regions for Martian Years 34, 35, and 36. The extinction is taken as the average between 320 and 360 nm. Shaded regions denote periods where there are no observations due to orbital geometry, while the white regions are where the spectrum is rejected. Both sunset and sunrise occultations are averaged in this figure. Figure 2: Example of SO extinction spectra (in red) showing the absorption due to water ice (in orange) with other aerosols here for comparison.

Introduction Hollows, flat-floored depressions with bright edges, are peculiar spectral units on the surface of Mercury [1,2], the only ones where an absorption band at 630 nm was detected in MDIS/MESSENGER multicolor images [3]. The feature was observed in hollows of Dominici and Hopper craters [4], extending from 559 to 828 nm in hollows of Canova and Velazquez craters [5], mainly ascribed to sulphides and chlorides [4,6], although additional components could occur, such as transitional elements, different from iron, on pyroxenes [5]. Additionally, hollows have flatter MDIS spectra [7], a strong curvature shortward of 600 nm [8] and the highest UV downturn shortward of 400 nm [8,9] in MASCS spectra [10]. We spectrally analysed the Praxiteles basin (198 km in diameter) [11], hosting hollows [12], faculae [13] and low-reflectance material (LRM) [14], the supposed parent material of hollows [12]. The floor is covered by low-reflectance blue plains (LBP) likely produced by effusive volcanism [15]. We detected a reflectance minimum at 828.4 nm in several MDIS spectra within the basin, suggesting the existence of a novel absorption band. Spectral examination and geological inspection of MDIS data link the absorption band to relatively fresh material exposed through hollows formation and/or mass wasting. Dataset and toolsThe Praxiteles basin was investigated by the MDIS/WAC multispectral image with a spatial resolution of 365 m/px. The cube is composed of 10491167 pixels and each pixel contains 8 filters, producing a reflectance spectrum from 430 to 1000 nm. The cube was photometrically corrected taking into account the topography and by applying the Hapke model using parameters derived from a global dataset [16].Spectral parameters used for the examination include spectral slope in the 480-830 nm range (VIS Slope), the UV downturn, and the band center and depth of the spectral features at 630 nm and 830 nm. The UV downturn is the ratio between a model reflectance at 430 nm extrapolated from the visible slope derived from the 480-560 nm observations (RM) and the measured reflectance in the same filter (Rm). The spectral features at 830 nm and at 630 nm were isolated by removing a spectral continuum defined by a fitted straight line between the absorption shoulders. Band Depth (BD) [17] and Band Center (BC) were calculated from the isolated bands. The band at 830 nm is not detectable for BD values lower than 3%, so that is the detection limit of the studied spectral feature. ResultsThe 830 nm band was found in the youngest and unnamed craters within Praxiteles basin, which we label as Prax-A (28.2°N, 60.3°W), Prax-B (26.1°N, 61.0°W), Prax-C (27.7°N, 60.8°W) and in three areas identified as Area1 (28.2°N, 60.3°W), Area2 (26.3°N, 58.7°W) and Area3 (28.4°N, 60.1°W), whose mean spectra are displayed in Fig.1.Fig.1. Mean spectra of the studied areas.The high-resolution MDIS/NAC images reveal a statistical distribution of this spectral feature on the edge of fresh gullies (Prax-A and Prax-C), on the edge of existing hollows (Prax-A, Prax-B, Prax-C, Area1 and Area2) and on the crater rim crest (Prax-A). No high-resolution MDIS images are available for Area3.The spectra with the 830 nm band are characterized by a moderate anti-correlation (Pearson coefficient of -0.65) between the UV downturn and VIS Slope (Fig.2, left): red-sloped spectra with a low UV downturn display only the 830 nm band (light red spectrum in Fig.2, right); flatter spectra with a higher UV downturn display both the 830 nm and the 630 nm features (dark red spectrum in Fig.2, right). Generally, we find that a higher intensity in the 630 nm feature is associated with a weakening of the 830 nm band.A preliminary comparison with MASCS spectra highlight a spatial correlation between a strong spectral curvature between 300 and 600 nm in MASCS data and the presence of the 830 nm feature.The band could be due to Fe+ or other transition metal ions in a crystalline structure, given the spectral similarity with laboratory spectra of common rock-forming minerals hosting Fe3+, Ti3+, Cr2+, Mn3+, Cu2+ ions [18]. The basin is placed in a region with high Fe/Si [19] and the low UV downturn could indicate a deepening of the oxygen-metal charge transfer band in Fe-rich minerals [20-22,9].Fig.2. Scatterplot of the UV Downturn vs VIS Slope (left), whose anti-correlation is linked to the occurrence of the 630 nm band together with the 830 nm spectral feature (right).ConclusionsThe novel spectral feature at 830 nm is found on the edge of hollows and bright gullies in Praxiteles basin. In addition, the 830 nm feature decreases in intensity and disappears when the spectra become similar to those of hollows. These discoveries suggest that the 830 nm feature could represent the most recent processes on Mercury, i.e. a phase preceding hollows' formation. References[1] Blewett et al. (2011) Science 333.[2] Vaughan et al. (2012) LPSC 1187.[3] Hawkins et al. (2007) SSR 131.[4] Vilas et al. (2016) GRL 43.[5] Lucchetti et al. (2018) JGR:Planets 123. [6] Barraud et al. (2023) Science Advances.[7] Blewett et al. (2009) EPSL 285.[8] Barraud et al. (2020) JGR: Planets 125.[9] Goudge et al. (2014) JGR: Planets 119.[10] McClintock and Lankton (2007) SSR 131.[11] Galluzzi et al. (2016) MemSAIt 87.[12] Thomas et al. (2014) Icarus 229.[13] Kerber et al. (2011) PSS 59.[14] Klima et al. (2018) Geophys. Res. Lett 45.[15] Denevi et al. (2013) JGR: Planets 118.[16] Domingue et al. (2016) Icarus 268.[17] Clark and Roush (1984) JGR 89.[18] Burns, 1993, Cambridge University Press.[19] Nittler et al. (2020) Icarus 345.[20] Rava and Hapke (1987) Icarus 71.[21] Cloutis et al. (2008) Icarus 197.[22] Greenspon et al. (2012) LPSC 2490. AcknowledgementsThis research was supported by the International Space Science Institute (ISSI) in Bern, through ISSI International Team project #552 (Wide-ranging characterization of explosive volcanism on Mercury: origin, properties, and modifications of pyroclastic deposits). Domingue L. Jozwiack, and O. Abramov were also supported by NASA grant 80NSSC21K0165 `Pyroclastic Eruption Conditions on the Moon and Mercury'. O.Barraud is supported by the Alexander Von Humboldt Foundation Research Fellowship program.

The process that led to the formation of our Solar System and the origin of the observed prebiotic compounds are among the most exciting open questions in modern astrochemistry. The first results of the Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST; PI: S. Yamamoto; Codella et al. 2021) ALMA Large Program suggest that the chemical composition and fate of future planetary systems strongly depend on the history of the parental protostellar envelope.I will present new FAUST high-angular resolution (50 au) observations of interstellar Complex Organic Molecules (iCOMs; i.e. organic molecules with at least 6 atoms; Ceccarelli et al. 2017) and dust continuum emission towards the Corona Australis (CrA) star cluster (see Figure 1). The CH₃OH emission reveals an arc-structure at ~1800 au from the protostellar system IRS7B along the direction perpendicular to the disk major axis (see Figure 2a). The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B (see Figure 1). The region inside the cone is probed by H ₂ CO (see Figure 2d), while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer (see Figure 2e). Taking into account the association with a previously discovered radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process.We derive for each cavity wall an average H2 column density of ∼ 7×1021 cm-2 , a mass of ∼ 9×10-3 M⊙ , and a lower limit on the dust spectral index of 1.4.These observations provide the first evidence of the shock and the conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar-System analogues.Figure 1: Left: SCUBA map at 450µm; Central: ALMA map of 1.3mm continuum emission from Sabatini et al (2024). Right: Zoom around IRS7B. Our ALMA continuum map reveals for the first time the dust grains in the walls of the cavity (cyan dashed lines) opened by the jet driven by IRS7B (cyan solid line).Figure 2: Moment 0 of (a) CH3OH-E (42,3 -31,2), (b) CH3OH-A (51,4-41,3), (d) p-H2CO (30,3-20,2), (e) SiO (5-4) lines, around the molecular arc (integrated from 0 to +12 km s−1). Cyan lines and arrows follow Figure 1. The white contours mark the 5σ emission. Small circles indicate the positions of the brightest spots in CH3OH (42,3-31,2), SiO (5-4), and p-H2CO (30,3-20,2), i.e. labelled "A", "B" and "C", respectively. Red cross indicates the position of SMM 1A (Figure 1). The green semicircle shows the ALMA Band 6 FoV, while the grey background delimits the region inside each ALMA pointing.

Introduction: Tolstoj quadrangle is located in the equatorial area of Mercury, between 22.5°N and 22.5°S of latitude and 144° and 216°E of longitude. In this work we present the results of the geological mapping (1:3M scale) we performed using the high resolution basemaps of MESSENGER data.Data: The main basemap used for the mapping is the MDIS (Mercury Dual Imaging System) 166 m/pixel BDR (map-projected Basemap reduced Data Record) monochrome mosaic compiled using NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) 750 nm-images. In order to better distinguish the surface morphologies, MDIS mosaics illuminated with high solar incidence angle, both from east (HIE) and west (HIW) [1] have been considered. Moreover, to distinguish spectral characteristics and topography of the surface, MDIS global color mosaics [2] and the MDIS global DEM [3], have been taken into account. Since Tolstoj quadrangle is encompassed in the equatorial region, its map was produced in an equirectangular projection. Then, the quadrangle has been mapped using ArcGIS at an average scale of 1:400k for a final output of 1:3M.Tolstoj quadrangle geological map: In H08 geological map geological contacts, lineaments, geological units, and surface features are shown (Fig.1). Geological contacts define the boundary of geologic units, that are surfaces characterized by the same morphology/texture, albedo/color characteristic, and stratigraphic position. Geological contacts are classified in: certain, where the contact is detected with confidence, and approximate, where the boundary between adjacent units is not well defined. Lineaments include: i) crater rims, distinguished between crater larger than 20 km and crater with a diameter ranging between 5 and 20 km, ii) tectonic structures, subdivided in grabens, wrinkle ridges, and thrusts, iii) pit rims, representing the crest of irregular pits that are interpreted to be volcanic vents. Surface features are grouped in crater chains and clusters, hollows and faculae (i.e. pyroclastic material).The final geological map shows the Caloris basin-related features dominating the most part of Tolstoj quadrangle. Indeed, the southern half of the basin is located in the upper left corner of quadrangle. Consequently, several units related to basin rim and ejecta material have been mapped (i.e. Odin, Van Eyck, Nervo, and Caloris Montes Formation). Moreover, smooth plains emplaced within and all around Caloris basin are the most extended volcanic deposits emplaced in H08. Intercrater plains are instead confined in the south-eastern margin of the quadrangle.Also structural framework is mainly linked with the basin with radial and concentric grabens located in its floor. These structures formed in response of extensive stresses due to the later stage of deformation of Caloris inner smooth plains [4]. Wrinkle ridges appear as low relief arches with a narrow superposed ridges. They are widespread on the Caloris smooth plains and their origin are attributed mainly to compressional stresses due to the subsidence of plains material [5]. In the inner smooth plains they show a preferential concentric and radial orientation with respect to the Caloris basin center; whereas the orientation of outer smooth plains' wrinkle ridges does not show a strong correlation with the basin. Also thrusts, that are low-angle inverse faults, have been mapped. They are located outside the Caloris basin but they are absent within its floor. Their origin are likely correlated to the planet contraction.Besides smooth plains, products of effusive volcanism, features related to explosive volcanism are also frequently detected. Interestingly, several volcanic vents have been identified in the inner Caloris smooth plains, aligned with the basin rim. They were surrounded by extended pyroclastic deposits appearing in bright yellow in MDIS enhanced global color mosaics. However, vents are not clustered only inside Caloris basin, but other crater floors are affected by this type of features.Finally, fields of hollows, small rimless depressions whose origin is related to volatiles loss [6], are detected. However, in Tolstoj quadrangle they are quite rare and are mainly located within the crater floor.Conclusions: In this work we presented the main characteristics of Tolstoj quadrangle geological map, dominated by the Caloris basin related features. This map will be merged with the other mapped quadrangles [7-14] and integrated into the global 1:3M geological map of Mercury [15], which is being prepared in support to ESA/JAXA (European Space Agency, Japan Aerospace Agency) BepiColombo mission.References: [1] Chabot et al.:LPS XLVII. Abstract#1256, 2016. [2] Denevi et al.:LPS XLVII. Abstract#1264, 2016.[3] Becker K. J., et al. AGU, Fall Meeting, abstract#P21A-1189, 2009.[4] Watters et al.:. Earth Planet. Sci. Lett.285, 283-296, 2009.[5] Watters and Nimmo: In: R.A. Schultz and T.R. Watters, eds., Planetary Tectonics, Cambridge Univ Press, 15- 80, 2010. [6] Blewett et al., JGR, 121, 1798-1813. [7] Galluzzi et al.: Geology, J. Maps, 12, 226-238, 2016.[8] Mancinelli, P. et al.: Journal of Maps, 12, 190-202, 2016. [9] Guzzetta L. et al.: Journal of Maps, 13, 227-238, 2017.[10] Wright J. et al.: Journal of Maps, 15, 509-520, 2019.[11] Pegg D. L.. et al.:. Journal of Maps, 17:2, 859-870, 2021.[12] Giacomini et al.: Journal of Maps, 18, 2022. [13] Malliband C. C., et al.: Journal of Maps, 19, 2023. [14] Man B. et al., Journal of Maps, 19, 2023. [15] Galluzzi V. et al.: Mercury 2024, abstract, 2024.Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0Fig.1 Geological map of Tolstoj quadrangle (H08)

Introduction: Tolstoj quadrangle is located in the equatorial area of Mercury, between 22.5°N and 22.5°S of latitude and 144° and 216°E of longitude. In this work we present the results of the geological mapping (1:3M scale) we performed using the high resolution basemaps of MESSENGER data.Data: The main basemap used for the mapping is the MDIS (Mercury Dual Imaging System) 166 m/pixel BDR (map-projected Basemap reduced Data Record) monochrome mosaic compiled using NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) 750 nm-images. In order to better distinguish the surface morphologies, MDIS mosaics illuminated with high solar incidence angle, both from east (HIE) and west (HIW) [1] have been considered. Moreover, to distinguish spectral characteristics and topography of the surface, MDIS global color mosaics [2] and the MDIS global DEM [3], have been taken into account. Since Tolstoj quadrangle is encompassed in the equatorial region, its map was produced in an equirectangular projection. Then, the quadrangle has been mapped using ArcGIS at an average scale of 1:400k for a final output of 1:3M.Tolstoj quadrangle geological map: In H08 geological map geological contacts, lineaments, geological units, and surface features are shown (Fig.1). Geological contacts define the boundary of geologic units, that are surfaces characterized by the same morphology/texture, albedo/color characteristic, and stratigraphic position. Geological contacts are classified in: certain, where the contact is detected with confidence, and approximate, where the boundary between adjacent units is not well defined. Lineaments include: i) crater rims, distinguished between crater larger than 20 km and crater with a diameter ranging between 5 and 20 km, ii) tectonic structures, subdivided in grabens, wrinkle ridges, and thrusts, iii) pit rims, representing the crest of irregular pits that are interpreted to be volcanic vents. Surface features are grouped in crater chains and clusters, hollows and faculae (i.e. pyroclastic material).The final geological map shows the Caloris basin-related features dominating the most part of Tolstoj quadrangle. Indeed, the southern half of the basin is located in the upper left corner of quadrangle. Consequently, several units related to basin rim and ejecta material have been mapped (i.e. Odin, Van Eyck, Nervo, and Caloris Montes Formation). Moreover, smooth plains emplaced within and all around Caloris basin are the most extended volcanic deposits emplaced in H08. Intercrater plains are instead confined in the south-eastern margin of the quadrangle.Also structural framework is mainly linked with the basin with radial and concentric grabens located in its floor. These structures formed in response of extensive stresses due to the later stage of deformation of Caloris inner smooth plains [4]. Wrinkle ridges appear as low relief arches with a narrow superposed ridges. They are widespread on the Caloris smooth plains and their origin are attributed mainly to compressional stresses due to the subsidence of plains material [5]. In the inner smooth plains they show a preferential concentric and radial orientation with respect to the Caloris basin center; whereas the orientation of outer smooth plains' wrinkle ridges does not show a strong correlation with the basin. Also thrusts, that are low-angle inverse faults, have been mapped. They are located outside the Caloris basin but they are absent within its floor. Their origin are likely correlated to the planet contraction.Besides smooth plains, products of effusive volcanism, features related to explosive volcanism are also frequently detected. Interestingly, several volcanic vents have been identified in the inner Caloris smooth plains, aligned with the basin rim. They were surrounded by extended pyroclastic deposits appearing in bright yellow in MDIS enhanced global color mosaics. However, vents are not clustered only inside Caloris basin, but other crater floors are affected by this type of features.Finally, fields of hollows, small rimless depressions whose origin is related to volatiles loss [6], are detected. However, in Tolstoj quadrangle they are quite rare and are mainly located within the crater floor.Conclusions: In this work we presented the main characteristics of Tolstoj quadrangle geological map, dominated by the Caloris basin related features. This map will be merged with the other mapped quadrangles [7-14] and integrated into the global 1:3M geological map of Mercury [15], which is being prepared in support to ESA/JAXA (European Space Agency, Japan Aerospace Agency) BepiColombo mission.References: [1] Chabot et al.:LPS XLVII. Abstract#1256, 2016. [2] Denevi et al.:LPS XLVII. Abstract#1264, 2016.[3] Becker K. J., et al. AGU, Fall Meeting, abstract#P21A-1189, 2009.[4] Watters et al.:. Earth Planet. Sci. Lett.285, 283-296, 2009.[5] Watters and Nimmo: In: R.A. Schultz and T.R. Watters, eds., Planetary Tectonics, Cambridge Univ Press, 15- 80, 2010. [6] Blewett et al., JGR, 121, 1798-1813. [7] Galluzzi et al.: Geology, J. Maps, 12, 226-238, 2016.[8] Mancinelli, P. et al.: Journal of Maps, 12, 190-202, 2016. [9] Guzzetta L. et al.: Journal of Maps, 13, 227-238, 2017.[10] Wright J. et al.: Journal of Maps, 15, 509-520, 2019.[11] Pegg D. L.. et al.:. Journal of Maps, 17:2, 859-870, 2021.[12] Giacomini et al.: Journal of Maps, 18, 2022. [13] Malliband C. C., et al.: Journal of Maps, 19, 2023. [14] Man B. et al., Journal of Maps, 19, 2023. [15] Galluzzi V. et al.: Mercury 2024, abstract, 2024.Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0Fig.1 Geological map of Tolstoj quadrangle (H08)

NOMAD [1] (Nadir and Occultation for MArs Discovery) is a multi-channel spectrometer onboard the ExoMars 2016 Trace Gas Orbiter (TGO), which began its observations in April 2018. Among other two (LNO and UVIS), the Solar Occultation (SO) channel covers the infrared (IR) spectrum from 2.3 to 4.3 µm (2320 to 4350 cm-1). Composed of an echelle grating in Litrow configuration, a total of 6 diffraction orders (with a typical width from 20 to 35 cm-1) are selected during each solar occultation using an Acousto-Optical Tunable Filter (AOTF) with a sample rate of about ~1 s, allowing a vertical resolution of typically 1 km. In order to optimize the information content that can be retrieved from the data, we analyzed Level 1 calibrated transmittances [2, 3] from four diffraction orders: 134 (3011-3035 cm−1), 136 (3056-3081 cm−1), 168 (3775-3805 cm−1) and 169 (3798-3828 cm−1). At the IAA-CSIC we developed processing tools specifically designed to handle and remove some systematics present in the NOMAD data, such as spectral shift and bending on the baseline of the spectra [4]. In addition, we performed an in-house characterization of the measurement noise using covariance matrices, identifying the true random component of the noise. This improvement allowed us to obtain homogeneous vertical profiles from the surface to an altitude about ~120 km. The profiles shown here have been retrieved combining two diffraction orders, this is, performing a global fit using spectra from two orders simultaneously. We combined pairs of orders 134 or 136 with 168 or 169 using them at different altitude ranges. The first two contain relatively weak absorption lines (S~10−21 cm−1/(molecule·cm−2) allowing the sample of the low atmosphere. On the contrary, the second set of orders contain strong lines close to center of the ν3 band(S~10−19 cm−1/(molecule·cm−2) which are useful to sample the upper atmosphere. This methodology is possible only when both orders have been measured during the same solar occultation, and although it limits the number of occultations available, it is necessary in order to avoid optically thick lines. Typically, we used low altitude orders (134/136) below 60 km and high altitude orders (168/169) above 60 km.The content presented here is a follow-up work building upon several previous studies [5-8]. We extended the dataset selecting a total of 6561 occultations taken during Martian Years (MY) 34,35 and 36. We discuss detailed seasonal and latitudinal maps, showing the vertical distribution of the water vapor abundance and its variability thought the year. A summary of this work can be seen in Fig. 1, where we show the seasonal variation of all the retrieved water vapor profiles.Figure 1: Vertical distribution of water vapor during MYs 34, 35 and 36 for the Northern (middle panel) and Southern (bottom panel) hemispheres. Horizontal axis shows the Solar longitude. Top panel indicates the latitude and local time of the observations.Figure 1 clearly shows a repeated pattern in both hemispheres. Water vapor is present in a more vertically extended range during the Southern summer (perihelion season) whereas it is mostly confined to low altitudes (below 20 km) during the aphelion season, which corresponds to the Northern summer. Also, the characteristic Global Dust Storm (GDS) that took place in 2018 can be seen at the beginning of the MY 34 (LS~190º), showing a distinctive peak in water abundance in the northern hemisphere that is not repeated again.In addition, we analyzed in detail the latitudinal distribution of water vapor during the perihelion season. We noticed a strong vertical plume at 60ºS - 50ºS injecting H2O into the mesosphere, reaching abundances of about ~50 ppmv at 100 km. We observed this event repeatedly in the three Martian years analyzed, although with inter-annual variations in both its magnitude and timing. The plume showed a weaker structure with less abundance during MY 34. We suggest that this difference respect to MYs 35 and 36 could possibly due to indirect effects of the MY 34 GDS. A summary of this analysis is presented in Fig. 2 where a storng water vapor injection can be seen in MYs 35 and 36 (panels B and C respectively).Figure 2: Water vapor latitudinal variation during LS = 260º-280º for MYs 34, 35 and 36 (panels A, B and C respectively). Dots in top panels indicate latitude, Solar Longitude and Local Solar Time of the observations.AcknowledgmentsThe IAA/CSIC team acknowledges financial support from the Severo Ochoa grant CEX2021-001131-S and by grants PID2022-137579NB-I00,RTI2018-100920-J-I00 and PID2022-141216NB-I00 all funded by MCIN/AEI/ 10.13039/501100011033. A. Brines acknowledges financial support from PRE2019-088355 funded by MCIN/AEI/10.13039/501100011033. ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by Spanish Ministry of Science and Innovation (MCIU) and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1, ST/Y000234/1 and ST/X006549/1 and Italian Space Agency through grant 2018-2-HH.0. This project has received funding from the European Union's Horizon 2020 grant No 101004052. US investigators were supported by the NASA. Canadian investigators were supported by the Canadian Space Agency. We want to thank M. Vals, F. Montmessin, F. Lefevre, F. Forget and the broad LMD/IPSL team supporting the Mars PCM.References1. Vandaele, A. C. (2018). Space Science Reviews, 214.2. Thomas, I. R. (2022). Planetary and Space Science, 218.3. Trompet, L. (2023). Journal of Geophysical Research: Planets, 128(3).4. López-Valverde, M. A. (2023). Journal of Geophysical Research: Planets, 128(2).5. Brines, A. (2023). Journal of Geophysical Research: Planets, 128(11).6. Aoki, S. (2019). Journal of Geophysical Research: Planets, 124(12).7. Aoki, S. (2022). Journal of Geophysical Research: Planets, 127(9).8. Villanueva, G. L. (2022). Geophysical Research Letters, 49(12).

NOMAD [1] (Nadir and Occultation for MArs Discovery) is a multi-channel spectrometer onboard the ExoMars 2016 Trace Gas Orbiter (TGO), which began its observations in April 2018. Among other two (LNO and UVIS), the Solar Occultation (SO) channel covers the infrared (IR) spectrum from 2.3 to 4.3 µm (2320 to 4350 cm-1). Composed of an echelle grating in Litrow configuration, a total of 6 diffraction orders (with a typical width from 20 to 35 cm-1) are selected during each solar occultation using an Acousto-Optical Tunable Filter (AOTF) with a sample rate of about ~1 s, allowing a vertical resolution of typically 1 km. The high spectral resolution (λ/∆λ ~17000) and the relatively low signal to noise ratio of this instrument (~2500) make NOMAD SO suitable for the detection of hydrogen chloride HCl. This trace species, although until now considered to be a negligible compound in the Martian atmosphere [2, 3], it has been detected systematically by two instruments onboard TGO: the Atmospheric Chemistry Suite (ACS) [4] and more recently NOMAD [5]. Several works suggest the surface of Mars to be a source of chloride minerals and perchlorate salts [6], which along with interactions surface-atmosphere could allow for chlorine photochemistry happening on the martian atmosphere. On Earth, one of the main sources of HCl is the volcanic activity [7], so the detection of this species on Mars may be an indicator of active geological processes. Multiple ongoing studies are trying to characterize the climatology of HCl on Mars, currently not completely understood, looking for possible relationships between temperature and other atmospheric species such as dust or water vapor.At the IAA we have carried out a study with the objective of identifying not only sources but seasonal variability of HCl by analyzing NOMAD spectra. This early study [8] using a simplified processing pipeline allowed us to detect HCl during the perihelion season of MYs 34 and 35, confirming previous results from [5]. Here, as a follow-up work of that study, we applied a modified version of our IAA-CSIC NOMAD processing pipeline [9-12] in order to increase the sensitivity required for the detection of weak HCl absorption lines, we have analyzed a total of 2536 solar occultations measured during Martian Years 34, 35 and 36. Among those modifications, we improved the methodology used for the characterization of the spectral continuum, now being able to detect systematic oscillations with amplitudes similar to the measurement noise (10-4 in transmittance). We have performed retrievals using NOMAD spectra from diffraction orders 129 (2899 - 2922 cm-1) and 130 (2921 - 2945 cm-1). In order to obtain robust HCl detections, we used the spectra from three detector bins on each ocucltation, retrieving an independent vertical profile form each bin. We present HCl vertical profiles and the seasonal variability of this species from a climatological view, revealing possible links with water vapor and dust.AcknowledgmentsThe IAA/CSIC team acknowledges financial support from the Severo Ochoa grant CEX2021-001131-S and by grants PID2022-137579NB-I00, RTI2018-100920-J-I00 and PID2022-141216NB-I00 all funded by MCIN/AEI/ 10.13039/501100011033. A. Brines acknowledges financial support from the grant PRE2019-088355 funded by MCIN/AEI/10.13039/501100011033 and by 'ESF Investing in your future'. ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by Spanish Ministry of Science and Innovation (MCIU) and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1, ST/Y000234/1 and ST/X006549/1 and Italian Space Agency through grant 2018-2-HH.0. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004052. US investigators were supported by the National Aeronautics and Space Administration. Canadian investigators were supported by the Canadian Space Agency. We want to thank M. Vals, F. Montmessin, F. Lefevre, F. Forget and the broad LMD/IPSL team supporting the continuous development of the Mars PCM. References1. Vandaele, A. C. (2018). Space Science Reviews, 214, 1-47.2. Hartogh, P. (2010). Astronomy & Astrophysics, 521, L49.3. Villanueva, G. L. (2013). Icarus, 223(1), 11-27.4. Korablev, O. (2021) . Science Advances 7, eabe4386.5. Aoki, S. (2021). Geophysical Research Letters 48, e2021GL092506.6. Glavin, D. P. (2013). Journal of Geophysical Research: Planets 118, 1955-1973.7. Graedel, T. (1995) . Global Biogeochemical Cycles 9, 47-77.8. Belmote-Gimenez, A. (2023) Mater Thesis, University of Granada.

IntroductionMercury's hollows are small (tens of meters to few kilometers), localized, shallow depressions found on the surface of the planet. They are unique features distinct from their surroundings, and characterized by their appearance as irregular, bright spots, often found clustered in groups called hollow fields. Their origin is still not fully understood, but they are believed to be related to sublimation processes, where volatile materials [1; 2] close to the surface directly transition from solid to gas due to exposure to high temperatures due for example to intense sunlight or volcanic activity [3]. However, as the ESA/JAXA BepiColombo spacecraft is approaching Mercury [4], understanding the specific geological and environmental factors influencing the formation and distribution of hollows remains a key research objective [5]. MethodsTo improve our grasp on this topic, we herein renew the previous hollows dataset provided by [7] by updating the database and its degree of detail. Indeed, in this work we make use of MESSENGER end of mission mosaic datasets [6] in order to exploit the most updated data that were not yet available at the time when the previous database [7] was released. We provide GIS-ready polygonal features to encompass areas where fields of hollows are present on the surface and present a statistical analysis on their occurrence across the surface. We also provide statistical information on the craters hosting hollows and compare them to the global crater database [8]. This study aims at understanding the global stratigraphic occurrence of hollows through a statistical approach, setting a foundation for future multidisciplinary research, rather than focusing solely on their intrinsic morphology or composition. By compiling this updated global database of hollows, we can preliminarily explore their stratigraphic occurrence to investigate their debated formation origins. Since most of the population of hollows is contained within impact craters, which by definition excavate the crust of the planet exposing the underlying stratigraphy, it is possible to investigate whether relationships exist between the presence of hollows and specific crater populations and, in turn, constrain whether there is one or more identifiable source layers. Specifically, to profitably test these hypotheses, we compared the population of craters containing hollows (c. 430 in total) and an existing dataset of craters on Mercury [8]. This database, that we will refer to as the global population, is based on a thorough mapping effort that provided a broad and nearly global coverage of Mercury craters by classifying them into 5 morphological classes [8]. Although other datasets exist, and this one includes only craters with diameters larger than 40 km, it represents one of the most recent and complete datasets available that also considers morphological classification for a statistically significant number of craters. By comparing diameter, depth, and degradation between the two crater datasets, it is possible to reveal differences between the global crater population and the subpopulation of hollow containing craters. This helps understanding whether the hollow containing craters are a random subset of the global population, and thus closely replicates its main characteristics (i.e. diameter, elevation, degradation), or not. ResultsHollows occurrence seems to be ubiquitous and variously spatially correlated with multiple surface morphologies, foremost among them impact craters. In conclusion, the nuanced relationship between hollows and Mercury's geological history unveils the intricate interplay of endogenous and exogenous processes. The dynamic nature of hollows, with their occurrence in association with both impact and volcano-tectonic events, hints at a complex history of material redistribution on the planet's surface. Overall, we provide quantitative evidence supporting: 1- the lack of a single (or a limited and measurable number) planet-wide unit bearing the volatile materials necessary for hollows formation due to: (i) widespread depth range of hollows appearance in the crust; (ii) lack of correlation between hollow emergence and one or more geological units (including color units). 2- the short-lived nature of hollows due to: (i) a significant lack, or total absence, of hollows in older and more degraded craters compared to younger, fresher craters; (ii) a higher abundance of hollows correlated to tectonic structures or pits when located within older and degraded craters. Hence, from a stratigraphic point of view, this work highlights the likely existence of widespread presence of a both horizontally and vertically discontinuous volatile-bearing formation. References[1] Blewett, D., et al. (2013). JGR-Planets, 118, 1013-1032. [2] Barraud, O., et al., (2020). JGR-Planets, 125, e2020JE006497. [3] Blewett, D., et al. (2011). JGR-Planets, 116(E12). [4] Benkhoff, J., et al., (2021). Space Sci Rev, 217(8), 90. [5] Rothery, D., et al., (2020). Space Sci Rev, 216, 1-46. [6] Denevi, B.W., et al., (2018). Space Sci. Rev. 214, 2. [7] Thomas, R. J., et al., (2014), Icarus, 229, 221-235. [8] Kinczyk, M. J., et al., (2020). Icarus, 341, 113637. AcknowledgementAuthors from Italian Institutes acknowledge Italian Space Agency (ASI) support within SIMBIOS-SYS project under ASI-INAF agreement 2017-47-H.0. Some of the authors gratefully thank the European Union - NextGenerationEU and the 2023 STARS Grants@Unipd programme - "HECATE project" support.

IntroductionHollows are one of the peculiar surface features that was highlighted by the MESSENGER mission [e.g. 1]. They have morphological evidence showing flat-floored and rimless depressions often clustered in fields and relatively bright. They are also associated with a peculiar cyan color within the RGB of the enhanced color mosaic [2]. This color variation is mainly indicating a higher reflectance, in particular within the visible, and a consequent bluer slope within the 400-1000 nm wavelength range [3]. In a few cases, such as the hollow field in the Dominici crater, literature has reported a potential absorption band in that spectral range [e.g. 4,5] with an inflection around 1000 nm, which could indicate an absorption [5]. The putative absorption has been attributed to some sulfides (e.g. CaS, [4]) or to the presence of transitional elements, different from iron, on silicates [5]. Here we investigate different hollow fields and other bright features with hollow-like (i.e. Dominici-like) spectral properties, present in the Kuiper quadrangle.Data and Analytical ApproachMDIS 8 color mosaics have been produced with the same process described in [6] at different spatial resolutions taking care of the original image resolution, avoiding those frames with extreme geometrical values and pixel resolution larger than 3.6 km (see also [7]). We investigate the spectral properties of the hollow fields mapped by [8], as well as other bright features with cyan colors in the enhanced color mosaics.ResultsThe spectral properties of the investigated features show in general a bluer slope and higher reflectance with respect to those of the Hermean average spectrum (see fig.1). Interestingly, the brighter features show the same spectral properties of Dominici hollow field present on the central peak: a potential absorption around 630-750 nm and an inflation towards 1000 nm. Hollow fields with these properties (first group) are, for instance, in Homer, Warhol, and Abu Navas craters. A second set of features show similar spectral properties with a slightly lower reflectance, and weaker, but still recognizable, absorption and inflation. This behavior is present for example in hollow fields of Chaickowski, Yets, Veronese craters, as well as some small bright features (probably small craters) like those closer to Yets and Beck craters. A third group with reflectance variable between the previous two groups shows the same spectral shapes but the absorption around the 630-750 nm is absent whereas the inflation towards the longer wavelengths is still present. In this case we have, for example, the second hollow field in Dominici and Abu Navas craters, with other small craters within the quadrangle. Further cases, in general those with a lower reflectance, show an intermediate slope, no absorption band, and a reduced, in some cases absent, inflection.DiscussionAll morphologically recognizable hollow fields present in the Kuiper quadrangle, maintain the same peculiar spectral properties reported in literature [4,5]. Spectra are dominated by a bluer spectral slope, they are relatively high in reflectance, but they can span from very bright up to an intermediate reflectance. Some of them clearly show an absorption like the one observed in the hollow field on the central peak of Dominici (first group); others show weaker absorption or inflection, up to spectra with a less blue slope and absence of the band and inflection. In general, those spectral properties peculiar to the hollow fields decrease with the reflectance of those regions. Where spectral properties of hollows become less evident, we find features like hollows but also like bright spots and small, fresh craters.Hollow-like spectral properties seem to suggest that they are compositionally different from the surrounding and several cases, non-only in Dominici crater, since to have the same spectral evidence. Nevertheless, a transition between the materials present in the hollow fields and the cases where spectral properties become closer to the average spectrum of a hermean terrain seems to be present. Interestingly, this hollows-like material seems to be present in regions where we cannot clearly identify the presence of hollow fields by means of photo-interpretation yet. ImplicationsThe variation of spectra within the different cases could be probably related to 1) a possible variation of the composition of the hollows, 2) mixing of the hollow-like constituent with different material from the surrounding terrains, 3) a different number density of hollows within the hollow fields, or 4) an increasing effect of space weathering (i.e. aging) or physical degradation of the hollow fields.Moreover, there is evidence that similar spectral properties are present both in regions where hollow fields can be clearly identified, and in other small bright regions, often clearly associated with craters, where hollows have not been identified yet. This could indicate that the image resolution does not permit identifying hollow fields in those areas. Conversely, the similitude of spectral properties between hollow fields and other features could indicate the composition of a material forming part of the crust of Mercury, only exposed on relatively fresher regions.Our future activity will focus on understanding better if the hollows-like material can be present not only in hollow fields and why we see a variation in its spectral properties. Moreover, we will suggest which of those could be the most interesting targets for the BepiColombo mission.AcknowledgmentThis research is funded from the Italian Space Agency (ASI) within SIMBIOS-SYS project under ASI-INAF agreement 2017-47-H.0. CC, FZ, GL, MM, VG were also supported by Europlanet RI20-24 research grant agreement No. 871149-GMAP.References[1] Blewett et al. (2011) Science 333. [2] Denevi et al. (2011) Science 333. [3] Blewett et al. (2013) JGR 118. [4] Vilas et al. (2016) GRL 43.[5] Lucchetti et al. (2018) JGR 123. [6] Zambon et al. (2022) JGR 127. [7] Carli et al. 2022, CNSP XVII, Abstract#. [8] Giacomini et al. 2023, Journal of Maps 18.

The ExoMars Trace Gas Orbiter (TGO) mission is a joint venture of the space agencies ESA and ROSCOSMOS which was launched in 2016 and carries onboard instruments dedicated to studying the trace gas compositions of the Martian atmosphere. NOMAD (Nadir and Occultation for MArs Discovery) is one such instrument that housed three observing channels named UVIS (the Ultra Violet and Visible Spectrometer), LNO (Limb Nadir Occultation) and SO (Solar Occultation) to scan the Martian atmosphere in nadir and limb geometries [1]. The SO channel of NOMAD operates in the IR (Infra-Red) region of the solar spectrum in the wavelength range 2.3 - 4.3µm. The SO spectrometer contains an echelle grating which can produce diffraction patterns of multiple orders but only one order is allowed to fall onto the detector selected by an AOTF (Acousto Optical Tunable Filter) filter. Spectral region of diffraction orders from 186 - 191 contains well-separated and strong absorption lines of CO. The NOMAD-SO channel is using diverse diffraction orders to monitor the CO due to its importance in understanding the dynamics and chemistry of the Martian atmosphere. CO is produced in the upper Martian atmosphere by the photolysis of CO2 and destroyed by the hydroxyl (OH) radicals in the lower atmosphere. Hydroxyl radicals thus recycle CO into CO2. The study of the CO vertical distribution is important to understand the photo-chemical stability of the atmosphere. CO not only links the chemistry of the carbon and odd hydrogen families but is a long-lived species which also serves as a dynamical tracer. At IAA-CSIC we have developed a preprocessing scheme to clean the NOMAD calibrated data from a number of systematics and prepare them for inversion of different atmospheric species [2,3,4,5]. Those systematics are spectral shift of the absorption lines and spectral bending which occurs due to thermally induced mechanical stress on the detector [6]. The work presented here is in continuation with our previous work on the retrievals of CO [3] wherein the retrieval scheme has been described in detail. Our previous study reveals two crucial factors that need to be considered for a correct CO retrieval, one is the saturation of spectral lines in diffraction orders 186 and 190, those used in our work to derive CO. The second one is the use of observed temperature and pressure in the retrieval rather than the climatological T/P from GCMs (general circulation model). For order 190, the absorption lines become saturated below 70 km while for orders 186, the lines remain unsaturated for most of the atmospheric region below this altitude. In the altitudes above 70 km, the absorptions in 186 are dominated by random noise but the lines in 190, due to their strength remain clear. Due to this fact, an adequate combination of these two diffraction orders is recommended for performing CO inversions from TGO solar occultation data.In this work, we will present the improved CO vertical densities using this strategy and the impact on the CO distribution.References[1] Vandaele, A. C., Lopez-Moreno, J. J., Patel, M. R., Bellucci, G., Daerden, F., Ristic, B., ... & NOMAD Team. (2018). NOMAD, an integrated suite of three spectrometers for the ExoMars trace gas mission: Technical description, science objectives and expected performance. Space Science Reviews, 214, 1-47.[2] López-Valverde, M. A., Funke, B., Brines, A., Stolzenbach, A., Modak, A., Hill, B., ... & NOMAD team. (2023). Martian atmospheric temperature and density profiles during the first year of NOMAD/TGO solar occultation measurements. Journal of Geophysical Research: Planets, 128(2), e2022JE007278.[3] Modak, A., López-Valverde, M. A., Brines, A., Stolzenbach, A., Funke, B., González-Galindo, F., ... & Vandaele, A. C. (2023). Retrieval of Martian atmospheric CO vertical profiles from NOMAD observations during the first year of TGO operations. Journal of Geophysical Research: Planets, 128(3), e2022JE007282.[4] Stolzenbach, A., López Valverde, M. A., Brines, A., Modak, A., Funke, B., González-Galindo, F., ... & Vandaele, A. C. (2023). Martian atmospheric aerosols composition and distribution retrievals during the first Martian year of NOMAD/TGO solar occultation measurements: 1. Methodology and application to the MY 34 global dust storm. Journal of Geophysical Research: Planets, 128(11), e2022JE007276.[5] Brines, A., López-Valverde, M. A., Stolzenbach, A., Modak, A., Funke, B., Galindo, F. G., ... & Vandaele, A. C. (2023). Water vapor vertical distribution on Mars during perihelion season of MY 34 and MY 35 with ExoMars-TGO/NOMAD observations. Journal of Geophysical Research: Planets, 128(11), e2022JE007273.[6] Liuzzi, G., Villanueva, G. L., Mumma, M. J., Smith, M. D., Daerden, F., Ristic, B., ... & Bellucci, G. (2019). Methane on Mars: New insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration. Icarus, 321, 671-690.Acknowledgements:The IAA/CSIC team acknowledges financial support from the Severo Ochoa grant CEX2021-001131-S and by grants PID2022-137579NB-I00, RTI2018-100920-J-I00 and PID2022-141216NB-I00 all funded by MCIN/AEI/ 10.13039/501100011033. A. Brines acknowledges financial support from the grant PRE2019-088355 funded by MCIN/AEI/10.13039/501100011033 and by 'ESF Investing in your future'. ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University).

The present communication is based on preliminary results within the PRIN 2022 PNRR project entitled "Low-cost, high-safety hydrogen storage into chemically-enhanced clathrate hydrates for energy storage in planetary infrastructures" (Brave New Worlds, CUP D53D2301693000, funded by the European Union - Next Generation EU) led by the University "G. d'Annunzio" of Chieti - Pescara, with the collaboration of University "Aldo Moro" of Bari, and the National Institute for Astrophysics of Catania (INAF) as research units. The aim of the project "Brave New Worlds" is to develop low-cost, high-safety media for the storage of hydrogen, which also have minimal technologic and maintenance requirements. Target storage media will be ideally suitable for space-based infrastructures on near planets (e.g., Mars) or satellites (e.g., Moon), where hydrogen will be produced from planetary water bodies by solar cell-powered electrolysis.Currently, hydrogen is stored in pressurized cylinders, metal hydrides and similar compounds that require high energy consumption to store and recover H2, or in liquefied form. None of those storage technologies are suitable for planetary infrastructures, because of the high spacecraft payloads needed to carry cylinders, compressors, metallic media and other highly technological devices to be deployed and assembled in situ. Furthermore, the control of the compression of hydrogen into cylinders, or the temperature cycles for the sorption onto metal hydrides, or for liquefaction, require sophisticated, failure-prone control appliances.The storage media developed in the present work are clathrate hydrates of hydrogen, a class of supramolecular solids consisting of water molecules organized in cage structures that can host one or more gas molecules. These systems represent a safer, technologically simpler, and cheaper alternative for large-scale hydrogen storage than traditional storage methods. Clathrate hydrates are usually formed under conditions of pressures around 5-10 MPa and temperatures of around 250-280 K, or, importantly for the present case, under lower pressures and very low temperatures.Thus, important features that we are exploiting are the following:clathrate hydrates are essentially made up of water, an economical, ecological and safe compound par excellence. Having a potentially infinite life cycle, water is an ideal material for this purpose. Water is found on (or just below) planet and satellite surfaces. Sun-shaded or deep crater areas of planets and satellites reach temperatures as low as 30 K Hydrogen hydrates can form at very low temperatures under mild gas pressures In the present work, we show how to overcome some critical points of hydrogen storage in clathrates, namely (i) slow capture kinetics, and (ii) low gravimetric content. As for point (i), here we report processes and molecules for improving the kinetics of the process of 1-2 orders of magnitude. The increase of the gravimetric content (point (ii)) has been addressed with the design and test of stabilizers (co-formers) of the hydrate cages, through a combination of rational design, quantum mechanical and molecular dynamics approaches, stochastic methods, and chemical synthesis. Preliminary results reported in the present contribution are: (i) the thermodynamic equilibrium curves of binary hydrogen hydrates in presence of stabilizers (tetrahydrofuran, cyclopentane; Fig. 1); (ii) the kinetics of formation of hydrogen hydrates under water-in-oil or oil-in-water emulsion systems (Fig. 2); and (iii) Raman spectroscopy data showing the presence of hydrogen within the small hydrate cages (512 dodecahedra) and possibly also within the large cages (51262 polyhedra) of sII crystal structures (Fig. 3).The final goal will be to develop a hydrogen storage medium with a gravimetric H2 content around 4 wt%, which is demonstrably competitive with current top technologies at a fraction of the technological level and economic cost. Fig. 1: P/T curve for THF/CP/hydrogen hydrate formation under different pressuresFigure 2: Kinetic P/T curves for the formation of THF/CP/H2 hydrate Figure 3: Raman spectrum of THF/CP/H2 hydrate at 70 bar Bibliography[1] Di Profio P, Arca S, Rossi F, Filipponi M. Int J Hydrogen Energy 2009;34:9173-80.[2] Di Profio P, Arca S, Germani R, Savelli G. J Fuel Cell Sci Technol 2007;4:49-55.[3] Di Profio P, Canale V, Germani R, Arca S, Fontana A. J Colloid Interface Sci 2018;516:224-31.

Introduction: Kelvin-Helmholtz instability (KHI) is considered one of the main processes of transferring solar wind energy, momentum and plasma inside magnetosphere. At the Earth, KHIs are observable in the form of waves (KHWs) within the magnetopause region between the anti-Sunward magnetosheath and the relatively stagnant magnetosphere. Over the past few decades, several missions (THEMIS, Cluster, MMS) have contributed significantly to our understanding of KHI. In this sense, it is well-known that (i) KHIs are a common phenomenon [1,2], (ii) KHIs can be generated under different IMF conditions [2], (iii) KHIs can lead to rolled-up vortices [3], (iv) KHVs drive the onset of magnetic reconnection (Vortex-Induced Reconnection) leading to development of Tearing Mode instability [4] and formation of magnetic islands, evolving into flux ropes [5], and (v) in the late nonlinear phase, vortex merging and secondary KHIs development in a wider latitudinal range [6]. In addition, [7] found that KHWs occur at the (flank) magnetopause for approximately 19% of that time. The occurrence of these waves is influenced by factors such as solar wind speed, Alfven Mach number and number density, and is mostly independent on the IMF magnitude. These conditions can be easily met when a perturbation propagates within the interplanetary medium, such as during the occurrence of a coronal mass ejection. Investigating the conditions under which KH and TM instabilities occur in the Earth environment, using simultaneous multipoint in-situ measurements and MHD simulations, is intriguing because it could provide insights into the flow dynamic nature at the magnetopause mixing layer. In this sense, we analyzed data from THEMIS and Cluster spacecraft considering two "target" Space Weather events occurred on 21 June 2015 (Case-1) and on 6 September 2017 (Case-2). The Model: Our analysis utilized a 2D MHD model [8] which describes the flow dynamics of the magnetopause mixing layer in a fluid limit. The simulation domain consists of a rectangular region in (x,y)-plane. On the local Cartesian grid, it is defined as follows: (i) neglecting the realistic curvature; (ii) considering the x-coordinate pointing to the direction along the velocity of the incident magnetosheath flow; (iii) assuming the y-coordinate in the direction downward to the Earth's center (from the magnetosheath to the magnetosphere) and (iv) ensuring a right-handed coordinate system with the z-coordinate.The used approach is flexible enough to represent any position on the dayside magnetopause. Results: In Case-1, we used our MHD model to interpret observational data and to investigate the potential development of KHVs on the dawn flank magnetopause as a consequence of the arrival of the ICME. Using THEMIS-E data, we found that at the magnetopause nose no rolled-up KHVs developed due to the absence of a shear between the two fluids. On the contrary, structures similar to magnetic islands appeared in By component very fast and vanished for 10 computational seconds. At the dawn flank magnetopause, the analysis of Cluster data revealed high flow and low magnetic shear between the magnetosheath and the magnetosphere. According to theoretical predictions, these conditions favour the onset of KHI. MHD simulations confirmed these considerations, finding that KHVs developed very rapidly and persisted up to 20 computational seconds (Figure 1), reaching almost MHD instability steady state. Regarding the TM instability, the MHD simulations revealed only an early development of magnetic islands (Figure 2), that persisted for half of the time of the KHVs evolution. In a global scale, these results indicate that vortices become unstable far away from the subsolar point in the direction of high flow shear. Figure 1. Case 1. Evolution of KH instabilities in density at the dawnward flank of the magnetopause, from 1 to 30 seconds. Input data obtained from the Cluster-C4 measurements. The dimensionless boundary conditions from the magnetosphere side and magnetosheath side are taken everywhere to be identical: BMSPx=-1.24, BMSHx=1.0, BMSPy=0.4, BMSHy=1, ρMSP =0.2, ρMSH=1, Re= 250 and Rm= 1 000, MA= 0.2. Blue region represents the magnetosphere whilst red region represents the magnetosheath. Figure 2. Case 1. Evolution of TM instabilities in By at the dawnward flank of the magnetopause. Same of Figure 1. In Case-2, using THEMIS-E data, we did not find any evidence of KHI owing to the extremely low flow and high magnetic shear. On the contrary, adopting Cluster-C4 data, MHD simulations revealed that the fast development of disturbances but no signatures of KHVs were visible. Additionally, magnetic islands appeared very fast as a result of high shear in the components of the magnetic field but rapidly vanished. References: [1] Hasegawa, H., et al. (2004). Nature, 430, 755-758.[2] Hasegawa, H., et al. (2006). JGR, 111, A09203.[3] Lin, D., et al. (2014). JGR, 119, 7485-7494.[4] Chen, Q., et al. (1997). JGR, 102, 151-162[5] Eriksson, S., et al. (2009). JGR, 114, A00C17.[6] Sisti, M., et al. (2019). Geophysical Research Letters 46, 11,597-11,605[7] Kavosi, S. and Raeder, J. (2015). Nature Communications, 6, 7019.[8] Ivanovski, S., et al. (2011). Journal of Theoretical and Applied Mechanics, 41, 31-42

Introduction: During its thirteen-year orbit around the Saturnian system (2004-2017), the Cassini mission produced an outstanding amount of data that made it possible to characterize Saturn, its rings, and its moons. Studying the composition and physical characteristics of Saturn's icy moons was one of the mission's main scientific objectives, aiming at understanding how different endogenic and exogenic processes interact to alter the moons' surfaces. The spectrophotometric properties of the MId-sized Saturnian icy Satellites (MISS: i.e., Mimas, Enceladus, Tethys, Dione, and Rhea) were extensively characterized in the 0.35-5.1 µm spectral range by the Visual and Infrared Mapping Spectrometer (VIMS, [1]) onboard the Cassini orbiter. This revealed surfaces dominated by water ice with variable amounts of contaminants, causing color changes (e.g., spectral reddening in the 0.35-0.55 µm interval), and albedo variations within and among the moons (Fig. 1).Figure 1. VIMS spectra of Saturn's icy moons, with the characteristic water ice bands at 1.5, 2., and 3 μm. The presence of non-icy compounds causes variations in albedo, VIS-NIR spectral slope, and UV downturn at 0.35-0.55 μm. Vertical dashed lines indicate VIMS' order sorting filter gaps. Adapted from [2].By establishing appropriate spectral indicators (such as spectral slopes in the UV-VIS and VIS-NIR wavelength intervals and the depth of water ice absorptions) connected to regolith grain size and water ice/contaminant abundances, several studies examined the spectral and compositional variability of the MISS, providing qualitative trends of average properties [2, 3, 4] and at disk-resolved scales [5-7]. However, this approach was unable to fully characterize the compositional and physical properties from a quantitative standpoint, because this information is still at least partially entangled in the spectral indicators.In an attempt to conduct a more quantitative analysis of the composition and physical characteristics of MISS's surfaces, VIMS hyperspectral data has been exploited through comparison with the outcomes of radiative transfer solutions (e.g., Hapke theory, 8), allowing to compute the spectra of different mixtures as a function of endmember abundances, mixing modalities, and grain size distributions. Such spectral modeling effort enables one to determine the spectral contribution of various compositional and physical properties to the observed spectral shape. In the case of MISS, similar attempts have been conducted in a small number of cases to constrain the composition of chosen terrains on selected targets (see [9] for Dione), or to determine the MISS compositional properties at full-disk scale [10, 2]. On the other hand, a systematic application of this methodology to perform a global compositional mapping from disk-resolved observations of MISS has not been performed yet.In this paper, we set ourselves to this task, starting with the largest of Saturn's mid-sized icy moons, Rhea. To this end, we take advantage of VIMS photometrically-corrected disk-resolved data of the satellite, made available by [7]. This data, by minimizing the observation geometry bias, allows us to characterize the intrinsic specral and albedo variability of the surface and, by means of systematic spectral modeling, map the distribution of water ice and contaminants across the surface, along with the regolith grain size.Method: we employ a VIMS photometrically-corrected spectral map of Rhea, adapting the methodology outlined in [7] (Figure 2, top panel). The spectral map is created by averaging photometrically corrected VIMS observations over a standard longitude-latitude grid with 0.5°x0.5° bin sampling. A hyperspectral cube with a spectrum assigned to each map position is the end product.Using Hapke's theory, we conduct systematic spectral modeling for every bin in the spectral map. The surface is characterized as a mixture of water ice, a macromolecular organic compound (tholin, causing the UV absorption), and amorphous carbon (as a darkening contaminant), adopting a paradigm similar to previous modeling attempts [11].Preliminary findings: we present a preliminary compositional map of Rhea in Figure 2 (middle panel). The spectral modeling results point to a surface composition dichotomy, where non-icy materials (carbon and tholin) are more abundant in the trailing hemisphere (longitudes 180°-360°) than in the leading one (longitudes 0°-180°), hosting larger amounts of water ice. The distribution of the various endmembers maps the albedo and color dichotomy of the surface, with a redder/darker trailing side contrasted to a bluer/brighter leading hemisphere (bottom panel of figure 2).The inferred endmember spatial variability will be examined in light of the exogenous processes affecting Rhea's surface, such as photolysis, flux of charged particles driven by Saturn's magnetosphere, contamination of exogenic darkening material, and bombardment from E-ring grains [12], accounting for their longitudinal dependence, along with cratering and endogenous processes that shaped the surface of Rhea.Figure 2. Top panel: 1.82-µm equigonal albedo map of Rhea in cylindrical projection [7]. Middle panel: RGB compositional map of Rhea (red: tholin abundance; green: carbon abundance; blue: water ice abundance). Bottom panel: Cassini Imaging Science Subsystem global color (IR, Green, UV) map (PIA18438, image credit P. Schenck, NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute).Acknowledgments: This work is supported by the INAF data analysis grant "MId-sized Saturnian icy Satellites Investigation by Spectral modeling" (MISSIS).References: [1] Brown et al., 2004. SSRv 115, 111-168. [2] Filacchione et al., 2012. Icarus 220, 1064-1096. [3] Filacchione et al., 2013. ApJ 766. [4] Hendrix, et al., 2018. Icarus 300, 103-114. [5] Stephan et al., 2016. Icarus 274, 1-22. [6] Scipioni et al., 2017. Icarus 290, 183-200. [7] Filacchione et al., 2022. Icarus 375. [8] Hapke, B., 2012. Theory of reflectance and emittance spectroscopy (Cambridge Univ. Press). [9] Clark et al., 2008. Icarus 193, 372-386. [10] Ciarniello et al., 2011. Icarus 214, 541-555. [11] Ciarniello et al., 2019. Icarus 317, 242-265. [12] Hendrix et al., 2018. Icarus 300, 103-114.

In this work we present an update on the analysis described in [15,21], focused on the characterization of Martian dust microphysical properties through the investigation of the TGO/NOMAD [1] UVIS and LNO channels' combined nadir data. These observations cover ultraviolet-visible and near-infrared wavelengths respectively, an extended range that allows constraining the dust densities and sizes. Spatially and temporally coincident data are analysed through the MITRA radiative transfer (RT) tool [2,3,4,16].Being the spectral surface albedo a key element in the RT simulations, we define a method to derive it by exploiting MEx/OMEGA data. As a by-product of this analysis, we plan to obtain a global Mars surface albedo map covering visual (VIS) and near-infrared (NIR) wavelengths.Introduction Airborne dust drives the Red Planet's thermal structure and climate [6,7,8,9,10], the distribution and circulation of atmospheric gases and has a role in triggering water ice clouds formation [5,17]. These mechanisms are affected by dust composition, abundance and microphysics. The investigation of NOMAD UVIS and LNO nadir data, can provide significant information on the properties of the integrated dust column down to the surface, hence contributing in our understanding of the evolution of Mars' atmosphere.Instrument and observations Among NOMAD's three spectrometers [1], UVIS and LNO channels can observe in nadir geometry in the ultraviolet-visible (UV-VIS, 0.2 - 0.65 µm) and NIR (2.2 - 3.8 µm) ranges respectively. Therefore, if combined, they allow retrieving the dust microphysical properties in the whole atmospheric integrated column. We consider observations encompassing from the second half of Martian Year (MY) 34 to the first half of MY37, an extended interval within which dust global and seasonal trends can be analyzed.Method UVIS data are exploited down to 0.36 μm, matching the lower wavelength of the surface albedo spectra ingested in the RT model. These are obtained by processing MEx/OMEGA data with a modified version of the SAS technique [14], nominally correcting the spectral shape from the gases and aerosols contribution. We modify the method in order to determine if the observations can be considered as aerosols-free, hence avoiding biases deriving from the assumed aerosols properties in the original correction. As far as LNO is concerned, only spectral orders from 168 to 202 are adopted [15,21], since they cover a wavelength range (2.20 - 2.55 μm) that is approximately devoid of strong absorption lines, hence allowing a reliable estimation of the spectral continuum. This way, no gases correction is required in our modified SAS.The retrievals are performed through MITRA tool, deriving the temperature-pressures profiles from [11] and considering dust optical constants from [12,13]. A benchmarking with the ones recently published in [19] is also foreseen.SummaryThis study presents an update of the method described in [15,21], focused on retrieving Martian dust microphysical properties from NOMAD UVIS and LNO nadir observations. We updated the method for deriving the spectral surface albedo in order to reduce eventual biases introduced in the original correction.We plan to analyze all spatially and temporally coincident UVIS and LNO observations, in order to track the evolution of dust properties in different MYs and verify how they compare to those retrieved at high altitude with NOMAD SO channel's data [20].AcknowledgementsExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB- BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by the Spanish MICINN through its Plan Nacional and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1, ST/Y000234/1 and ST/X006549/1 and Italian Space Agency through grant 2018-2-HH.0. The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the `Center of Excellence Severo Ochoa' award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). This work was supported by the Belgian Fonds de la Recherche Scientifique - FNRS under grant numbers 30442502 (ET_HOME) and T.0171.16 (CRAMIC) and BELSPO BrainBe SCOOP Project. US investigators were supported by the National Aeronautics and Space Administration. Canadian investigators were supported by the Canada Space Agency.References[1] Neefs, E., et al, 2015. Appl. Opt. 54, 28, 8494-8520.[2] Oliva, F., et al, 2016. Icarus 278, 215-237.[3] Sindoni, G., et al, 2013. EPSC2013.[4] Oliva, F., et al, 2018. Icarus 300, 1-11.[5] Vandaele, A.C., et al, 2019. Nature 568, 521-525.[6] Kahre, M.A., et al, 2008. Icarus 195, 576-597.[7] Korablev, O. ,et al, 2005. Adv. Space Res. 35, 21-30.[8] Gierasch, P.G., Goody, R.M., 1972. J. Atmos. Sci. 29, 400-402.[9] Pollack, J.,et al, 1979. J. Geophys. Res. 84, 2929-2945.[10] Määttänen, A., et al, 2009. Icarus 201, 504-516.[11] Millour, E., et al., 2019. EPSC-DPS 2019[12] Wolff, M.J., et al, 2009. J. Geophys. Res., 114, E9.[13] Wolff, M.J., et al, 2010. Icarus, 208.[14] Geminale, A., et al, 2015. Icarus 253, 51-65.[16]Aoki, S., et al. 2019. J. Geophys. Res.: Planets,124, 3482-3497.[15] Oliva, F., et al., 2021. 15th EPSC, EPSC2021-501.[16] D'Aversa, E., Oliva, et al., 2022. Icarus, 371, 114702.[17] Aoki, S., et al. 2019. JGR: Planets,124, 3482-3497.[18] Wolff, M. et al., 2019. Icarus, 332, 24-29.[19] Martinkainen, J., et al., 2023. APJ Suppl.Ser. 268:47[20] Stolzenbach, A., et al., 2023. JGR Planets, 128[21] Oliva, F., et al., 2024. XIX Congr. Naz. Sc. Pl., Bormio 2024.

Our is the only planet known with such complex chemistry that give rise to life. Numerous evidence suggests that molecular complexity had already begun and developed when the Solar System was an embryo inside a cold molecular cloud. In this presentation, I will present the major advances in our comprehension of chemistry during those ancient eons, based on what we observe in the young solar-like planetary systems forming in the Sun's vicinity today and our ability to understand them. I will also give an overview of the many challenges that remain to be overcome.

The composition of Phobos is poorly understood and its origin is still an open question [1]. There are two possible scenarios for its formation. Either Phobos is an asteroid captured by Mars, or it formed in-situ in a disc after a giant impact on Mars. The capture scenario is based on surface analysis, which shows a different composition compared to the Martian surface. However, the low density of Phobos suggests a high porosity and/or a significant amount of water ice, which could be the result of re-accretion of debris in Mars' orbit, favouring the in-situ formation scenario [2]. Therefore, if the Martian moon is formed by a giant impact on Mars, its composition will reveal the original conditions on Mars and provide insights into the formation of the planet and its young environment. On the other hand, if Phobos is a captured asteroid, its material will clarify the transport process of volatile components. For all these reasons, the acquisition of new nadir observations is essential to better characterise the composition of Phobos, which is the key to clearly explaining its origin. As part of the payload of the 2016 ExoMars Trace Gas Orbiter (TGO) mission, the Nadir and Occultation for MArs Discovery (NOMAD) instrument [3] has been observing the Martian atmosphere [4]. Albeit being mainly conceived for trace gases investigation, in nadir mode (NOMAD-UVIS and NOMAD-LNO), the spectrometers' suite can also measure surface features with a high spectral resolution in the UV and near-IR domain [5]. By focusing on the diffraction orders determining the instantaneous spectral ranges of LNO, these nadir observations can in principle be used to search for new spectral absorptions. In addition to the study of Mars, NOMAD is providing new nadir observations of Phobos [6]. This work focuses on the analysis of near-infrared observations using the NOMAD-LNO data set. For the near-infrared data, BIRA-IASB, with the participation of the ROB, has carried out several tests to correctly calibrate the instrument and determine the optimal observation window. Since March 2023, evaluation of the new Phobos near-infrared data, which include extended observing rates and modified diffraction order combinations, has been underway. At the time of writing, 29 observations of Phobos are available, using different diffraction order combinations. Data acquisition is concentrated on the search for carbonates (2.3 µm to 2.5 µm) and the hydrated mineral feature around 2.7 µm (2.5 µm to 2.8 µm). Due to the very low SNR of these observations, efforts have been made to reduce uncertainties: use of dark detector arrays to remove the background signal, geometric investigations to take account of illumination conditions and the combination of various NOMAD-LNO spectra. Ongoing analysis on NOMAD-LNO observations will be presented, with a quantitative comparison with previous spectral observations of Phobos [7-9] and laboratory measurements [10]. NOMAD is providing additional observations that remain crucial to planetary science. New data are indeed challenging our understanding of the composition, origin and formation of Phobos. In addition, this work is also preparing for the next Japanese mission, the Martian Moons eXploration (MMX) mission, in which the MMX spacecraft will observe and land on Phobos to collect surface samples to be returned to Earth for detailed observations of the Martian moon in particular using data collected by the infrared imaging spectrometer MIRS [11]. This work also contributes to the preparation of the next ESA Hera mission, which is scheduled to make a Mars flyby with observations of Martian Moons in spring 2025. Acknowledgements ExoMars is a space mission of the European Space Agency (ESA). The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB- BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493, 4000142490), by the Spanish MICINN through its Plan Nacional and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1, ST/Y000234/1 and ST/X006549/1 and Italian Space Agency through grant 2018-2-HH.0. This work was supported by the Belgian Fonds de la Recherche Scientifique - FNRS under grant numbers 30442502 (ET_HOME) and T.0171.16 (CRAMIC) and BELSPO BrainBe SCOOP Project. The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the `Center of Excellence Severo Ochoa' award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709).References[1] Fraeman, A. A., et al, 2012. JGR., 117, E00J15.[2] Le Maistre S., et al., 2019. Icarus 321, 272-290.[3] Neefs, E., et al, 2015. Appl. Opt. 54, 28, 8494-8520.[4] Vandaele, A.C., et al, 2019. Nature 568, 521-525.[5] Oliva, F., et al., 2022. JGR: Planets, 127, e2021JE007083. [6] Mason, J. P., et al., 2023. JGR: Planets, 128, e2023JE008002.[7] Fraeman, A. A., et al, 2014. Icarus 29, 196. [8] Rivkin, A. S., et al, 2002. Icarus, 156, 64.[9] Murchie, S. 1999. JGR, 104, 9069.[10] Poggiali, G., et al, 2022. MNRAS, 516, 465.[11] Barucci, et al., 2021. Earth Planets Space 73, 211

The Nadir and Occultation for MArs Discovery (NOMAD, [1]) spectrometer has been collecting Mars observations since 2018, providing a massive amount of information regarding its atmospheric composition, its vertical structure and bridging the gap between the previous knowledge of the lower atmosphere and the data from other missions (e.g., MAVEN) regarding atmospheric escape. The capability of the Solar Occultation (SO) channel to map the vertical structure of the atmosphere with very high (>1000) signal to noise ratio, very high spectral resolution (>17000) and high vertical sampling (0.5 to 2 km) is valuable in many contexts and has already allowed major new discoveries in the atmosphere of Mars. Among those, particularly significant ones include the contribution to the first detection of HCl in the atmosphere [2] and the characterization of its seasonal cycle and correlation with water vapor [3]. In addition, NOMAD data has been used to put stringent constraints on the upper limits for the long-searched CH4 and other hydrocarbons [4].Continuing the exploration of trace species is of fundamental importance because it enables to gain new insights into unknown aspects of how Martian atmospheric chemistry works, by revealing active cycles and exchanges between atmosphere and surface. In this work, we present results related to the quantification of stringent upper limits for two nitrogen species of interest, NH3 and HCN. Even though a nitrogen cycle on Mars is not expected, we aim at providing a quantification of upper limits for those species in different seasons and on a global scale, with the possibility to provide information to drive future observations and atmospheric modeling. Quantification of upper limits for those species was recently provided by ACS on board TGO [5], and by earlier ground-based studies (e.g. [6]), yet in this work we greatly expand the number of observations to full Martian Years and on a global scale, with the aim of exploring a wider base of data.Mapping of NH3 and HCN upper limits will be performed by using diffraction order 148 in NOMAD data. This order covers the spectral interval 3326-3353 cm-1 and contains strong spectral signatures of both gases. We analyze a wide dataset comprising more than 300,000 spectra taken at all altitudes between surface and 70 km, and at all latitudes, longitudes and seasons, between April 2018 and February 2024. Once CO2 and H2O abundances and rotational temperatures are fitted, the residual spectra are used to derive upper limits for NH3 and HCN, with the methods described in [4]. In this work, we will present the derived upper limits and draw some conclusions about their variability and implications for atmospheric modeling and future observation planning.References[1] A. C. Vandaele et al., Space Science Reviews, vol. 214, no. 5, Aug. 2018, doi: 10.1007/s11214-018-0517-2.[2] O. Korablev et al., Science Advances, vol. 7, no. 7, p. eabe4386, Feb. 2021, doi: 10.1126/sciadv.abe4386.[3] S. Aoki et al., Geophys. Res. Letters, vol. 48, no. 11, p. e2021GL092506, 2021, doi: 10.1029/2021GL092506.[4] E. W. Knutsen et al., Icarus, vol. 357, p. 114266, Mar. 2021, doi: 10.1016/j.icarus.2020.114266.[5] A. Trokhimovskiy et al., Icarus, vol. 407, p. 115789, Jan. 2024, doi: 10.1016/j.icarus.2023.115789.[6] G. L. Villanueva et al., Icarus, vol. 223, no. 1, pp. 11-27, Mar. 2013, doi: 10.1016/j.icarus.2012.11.013.

In the mesosphere on Earth, water ice clouds are frequently observed in the low-temperature region (below -130℃) at altitudes 80-90 km in the polar region. Two mechanisms have been proposed to explain the formation of these ice particles. One is homogeneous nucleation, in which condensation nuclei are formed from water vapour. The other is heterogeneous nucleation, in which substrates such as aerosol in the atmosphere undergo a phase change as nuclei. The latest theoretical study shows that heterogeneous nucleation is predominant in the nucleation of mesospheric clouds on Earth and that homogeneous nucleation is unlikely to occur, when compared to observed conditions (Tanaka et al., 2022; https://doi.org/10.5194/acp-22-5639-2022). This theory may apply to cloud formation in other planetary atmospheres. On Mars, mesospheric clouds like those on Earth have been observed, but there are still many unresolved issues. In particular, the nucleation has only been studied theoretically by applying a classical theory for the lower atmospheric clouds (Määttänen et al., 2005). The purpose of this study is to clarify the nucleation mechanism of the Martian mesospheric clouds by comparing the mesospheric cloud observations obtained at Mars with theory of Tanaka et al. (2022).We used the solar occultation spectral data obtained by the ultraviolet (UV) to visible (VIS) channel UVIS of the Nadir and Occultation for MArs Discovery (NOMAD) spectrometer on board the ExoMars Trace Gas Orbiter (TGO) to clarify the purpose. The observational data considered this study consist in 9249 atmospheric transmission profiles covering the period from Ls (areocentric longitude of the sun) = 163°in MY (Martian Year) 34 to Ls = 218°in MY 36 (2018/4/22-2022/4/30) (Figure 1). In this study, we derive the total optical depth along the line of sight (slant opacity) from the transmittance spectra (Streeter et al., 2021). We attempt to distinguish between water ice clouds and dust by comparing the slant opacity at 320 nm, where we assume a large contribution from water ice clouds, with the slant opacity of all aerosols, including dust, at 600 nm. The existence of water ice clouds is determined under the conditions that the optical thickness at 320 nm is larger than 0.01 at altitudes of 40-100 km and the slant opacity ratio (320 nm / 600 nm) is larger than 1.5. The atmospheric density, dust density, atmospheric temperature and cooling rate, dust particle size, and water vapour pressure of the atmospheric conditions are estimated from the Mars Climate Database (MCD) (version 5.3; Millour et al., 2012), a numerical atmospheric general circulation model, and applied to the theory of Tanaka et al. (2022) to investigate the possibility of homogeneous and heterogeneous nucleation.Following the thresholds described above, Martian mesospheric water ice clouds were detected in 966 out of 9249 altitude distributions (152 in MY 34, 615 in MY 35, and 199 in MY 36). In addition, the relationship between clouds and the background atmospheric field was investigated, and it was clear that clouds tend to form under atmospheric conditions where the water vapor pressure is above 10-5 Pa and the temperature is below 200 K (Figure 2). Out of the 966 data, data were selected by saturated vapour pressure corresponding to every 10 K in the range of 130 K to 180 K. These were compared with the conditions obtained by Tanaka et al. (2022) for whether homogeneous or heterogenous nucleation predominates (Figure 3). The results suggested that when the background atmospheric water vapour pressure is above 1.56-5 Pa (saturated water vapour pressure at 150 K) at the time of cloud formation, the Martian atmosphere can only have atmospheric conditions where heterogeneous nucleation occurs, as on Earth. This result clarified that heterogeneous nucleation is predominant in the nucleation of mesospheric water ice clouds on Mars. On the other hand, when the water vapour pressure is less than 9.40-7 Pa (saturated water vapour pressure at 140 K), it was indicated that the Martian atmosphere can have atmospheric conditions that produce homogeneous nucleation. In fact, some of the clouds detected at altitudes above 70 km below the saturated water vapour pressure of 140 K suggested the possibilities of homogeneous nucleation. The latter is unexpected because it is a Mars-specific event that cannot occur on Earth. Detailed analysis of the dust density and dust particle size using the results derived from the instrument's observation data is needed in the future, to clarify the atmospheric conditions under which homogeneous nucleation can occur, which is not seen on Earth but is suggested on Mars.

A new development in the field of adaptive optics (AO) on ground-based telescopes enables routine monitoring of changes on Io's surface at scales down to ~80km (achieved), or even down to ~50km (in the limit). Our observations, taken with SHARK-VIS on the Large Binocular Telescope (LBT) in Arizona, demonstrate this new capability. SHARK-VIS adds a visible light science channel to the AO system at LBT. While AO science in the infrared has been widespread for decades, visible-light AO science is new. SHARK-VIS, which saw first light at LBT on October 2nd, 2023, is one of only a few visible-light AO instruments on large telescopes.Our images of Io, taken soon after first light, are of the highest spatial resolution ever attained from a ground-based telescope. In addition to confirming known surface features, these images show a previously unseen plume deposit that obscures a portion of Pele's persistent red ring (see Fig. 1). This plume deposit, we believe, came as the result of a powerful eruption at Pillan Patera.Figure 1. The SHARK-VIS detection image on Nov. 23, 2023 (upper left), and again on Jan. 10, 2024 (upper right), and the reprojection of the Voyager and Galileo spacecraft-derived Io photomomosaic for Jan. 10, 2024 (center) (Becker & Geissler, 2005).To determine the date of the Pillan eruption, we analyzed thermal emission data collected by other telescopes over the last four years. Although these infrared images were necessarily taken at lower spatial resolution (due to the wavelengths used), the spatial resolution is sufficient to detect if and when excess thermal emission might have originated from Pillan Patera. These data show a spike in thermal emission, indicating a powerful eruption, during August 2021. Augmented with data from the Juno JIRAM instrument, we believe that this spike corresponds to the eruption responsible for the plume deposit seen in the SHARK-VIS images.These SHARK-VIS images serve as a demonstration of how adaptive optics at visible wavelengths will allow us to monitor surface changes on Io at regular intervals. Note that, prior to the SHARK-VIS observation, the most recent high-resolution imaging of the Pele region was from the New Horizons fly-by during March 2007. By April 2024, as seen by the visible imager on the Juno spacecraft, the red ring around Pele had repaired itself. Without the SHARK-VIS images, this resurfacing event would have never been detected.To date, regular monitoring of Io using ground-based facilities has largely been restricted to M-band (4.8 μm) imaging which, even using adaptive optics on 8-10 metre telescopes, yields spatial resolution of about 400-600 km. While there will always be a need for infrared images of Io for the thermal data that informs volcanology, visible-light images at 50-80km resolution allow us to "see" the landscape, to more accurately locate the effects of eruptions and associated features such as plume deposits.In our presentation, we will provide details of the Pillan plume deposit and its encroachment onto Pele's ring, and how that observation serves as a demonstration of how we will be able to monitor surface changes on Io going forward. We will also describe future ground-based systems that could produce imaging of Io down to spatial scales below 12km.