Introduction: On December 6, 2020, the Hayabusa2 mission successfully returned to Earth ~ 5.4 g of samples collected at the surface of the C-type asteroid Ruygu [1,2]. Its surface was first sampled on February 22, 2019, then on July 12, 2019, close to a 10-meter large artificial crater, so as to possibly access sub-surface material [3]. The collected samples are now kept at the Extraterrestrial Samples Curation Center of JAXA at ISAS in Sagamihara, Japan, for a first round of preliminary analyses, with the objective to characterize in a non-destructive manner both the bulk samples and a few hundreds of grains extracted from them [4]. In particular, the objective is 1) to support their further detailed characterization by the international initial analysis teams, which will start their activity in July 2021, and 2) to catalog the grains, accessible to the international community through AO selection, starting mid-2022.The preliminary characterization of these samples is being conducted with a visible microscope with four color filters, a FTIR spectrometer operating in the 1-5 µm range and MicrOmega, a hyperspectral NIR microscope developed at Institut d'Astrophysique Spatiale (Université Paris-Saclay/CNRS, Orsay, France), operating in the near-infrared range (0.99-3.65 µm) [5]. It is noteworthy that never before have the preliminary analyses of returned extraterrestrial samples included the characterization by a NIR hyperspectral microscope.Results: Preliminary outcomes of the analyses performed with MicrOmega will be presented at the conference. In particular, the question of the representativity of the samples collected by the Hayabusa2 spacecraft will be addressed thanks to the comparison of the spectra obtained by MicrOmega and the NIRS3 remote sensing IR spectrometer [6] which performed a spectral characterization (1.8-3.2 µm) of Ryugu's surface, including the sites of the samples' collection [7,8]. A preliminary analysis of the spatial compositional heterogeneity will be presented. Specific signatures, detected in grains typically present in

In this contribution we provide an update of the observations performed simultaneously (or quasi-simultaneously) by the two European satellites around Mars: Mars Express (MEX) and ExoMars 2016 Trace Gas Orbiter (TGO).The scientific objectives of both MEX and TGO missions are very complementary and there is a lot of synergy between the science teams, especially for the study of the atmosphere. Since the start of the TGO science operations in April 2018 we have executed hundreds of coordinated observations of the Martian atmosphere, first reported in [1] and now extended here. The science data obtained during these coordinated observations, both in sun occultation and nadir geometry, provide useful input for cross-calibration of the instruments, comparison of atmospheric vertical profiles and potential for the study of the temperature, composition, meteorology and climate of Mars.These observations are routinely coordinated by the instrument teams, in particular the spectrometers NOMAD and ACS onboard TGO [3,4] and SPICAM, OMEGA and PFS onboard MEX [5,6,7] and the Science Operations Centers (SOCs) of both missions [1, 2]:MEX-TGO Sun Occultations (within 15min and distance

Atmospheric gravity waves are mesoscale atmospheric oscillations in which buoyance acts as the restoring force, being a crucial factor in the circulation of planetary atmospheres since they transport momentum and energy, which can dissipate at different altitudes and force the dynamics of several layers of the atmosphere [1]. The source of these waves can be associated with the topographic features (orographic gravity waves) of surface, or with jet streams and atmospheric convection (non-orographic gravity waves). Recent modelling studies showed the strong role of gravity waves on diurnal tides on Mars atmosphere [2], however their characteristics are still not well constrained by observations. Here we report follow-up results from the detection and charaterisation of atmospheric waves on Mars’ atmosphere, using data from the OMEGA spectrometer onboard the Mars Express (MEx) space mission [3]. We used image navigation and processing techniques based on contrast enhancement and geometrical projections to characterise morphological properties of the detected waves. Our observations include the MEx nominal mission of the OMEGA instrument for the Martian years 27 and 28 (from January 2004 – January 2006 and from June – July 2007), constituted by 27 orbits and 4072 hyperspectral data QUBES. Every image was navigated and processed in order to optimise the detection of the wave packets and accurate characterisation of the wave properties such as the horizontal wavelength, packet width, packet length and orientation. The characterised wave-packets present a wide range of properties over a broad region of Mars’ globe specially in the evolution of gravity waves along the time. We also found that the detected waves occur at solar longitudes between 240-250º and 330-340º, which almost corresponds to the beginning and the end of the dust storm seasons. This preliminary result suggest a relationship between the presence of atmospheric waves and the dust storm events, already mentioned by Gondet et al. (2019). Acknowledgements: We acknowledge support from the Portuguese Fundação Para a Ciência e a Tecnologia of reference PTDC/FIS-AST/29942/2017, through national funds and by FEDER through COMPETE 2020 of reference POCI-01-0145-FEDER-007672, and through a grant of reference 2021.05455.BD. Funded by ESA Faculty research contract and Science Exchange Programme in the frame of MWWM - Mars Wind and Wave Mapping project. We would like to thank the late Dr Brigitte Gondet for her considerable help that made this work possible. References [1] Fritts, D. C.; Alexander, M. J. Gravity wave dynamics and effects in the middle atmosphere. Reviews of geophysics, 2003, 41.1. [2] Gilli, G., et al. Impact of gravity waves on the middle atmosphere of Mars: A non‐orographic gravity wave parameterization based on global climate modeling and MCS observations. Journal of Geophysical Research: Planets, 2020, 125.3: e2018JE005873. [3] Brasil, Francisco, et al. Characterising Atmospheric Gravity Waves on Mars using Mars Express OMEGA images–a preliminary study. In: European Planetary Science Congress. 2021. p. EPSC2021-188. [4] Gondet and J.-P. Bibring. Mars observations by omega/mex during the dust events from 2004 to 2019. In EPSC-DPS Joint Meeting 2019, volume 2019, pages EPSC–DPS2019, 2019.

We describe the completion of the MOCAAS project providing a global repository of secondary minerals formed through interaction with water on Mars. This work is based on the analysis of orbital imaging spectroscopy data from the OMEGA/Mars Express and CRISM/MRO near-infrared instruments. A database and a set of high-resolution global maps (200 m/pix) are produced which provide a large collection of these "aqueous" secondary mineral deposits, most of which were not previously reported. Several aqueous mineral classes are discriminated including hydrated silicates, hydrated silica, sulfate and carbonate salts. A preliminary statistical analysis on the database of aqueous mineral deposits is carried out, revealing significantly more widespread and diverse aqueous alteration on Noachian and Hesperian Mars than previously seen. Higher resolution local scale studies are also carried out over current and prospective rover landing sites on Mars, providing enhanced sensitivity to mineral detection and reachable science targets. Collectively, the data presented here at all scales is expected to foster synergy between orbital and landed missions, particularly for future missions and to pinpoint prospective resources for human exploration.

Atmospheric gravity waves are mesoscale atmospheric oscillations in which buoyance acts as the restoring force, being a crucial factor in the circulation of planetary atmospheres since they transport momentum and energy, which can dissipate at different altitudes and force the dynamics of several layers of the atmosphere [1]. The source of these waves can be associated with the topographic features (orographic gravity waves) of surface, or with jet streams and atmospheric convections (non-orographic gravity waves). Recent modelling studies showed the strong role of gravity waves on diurnal tides on Mars atmosphere [2], however their characteristics are still not well constrained by observations. We present here follow-up results [3] on the detection and characterization of atmospheric gravity waves on Mars using data from the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) [4] imaging spectrometer onboard the European Mars Express (MEx) space mission [5]. We used image navigation and processing techniques based on contrast enhancement and geometrical projections to characterize morphological properties of the detected waves. Our observations include 11 months’ worth of data from the first nominal mission of Mars Express, from January 2004 to November 2004. Every image was navigated and processed in order to optimise the detection of the wave packets and accurate characterisation of the wave properties such as the horizontal wavelength, packet width, packet length and orientation. We characterised almost 100 wave-packets across more than 1300 images over a broad region of Mars’ globe and our results show a wide range of properties specially in the evolution of gravity waves along the time, due to the time sampling and global coverage of MEx. Acknowledgments: This work is supported by Fundação para a Ciência e a Tecnologia (FCT)/MCTES through the research grants UIDB/04434/2020, UIDP/04434/2020, and through a grant of reference 2021.05455.BD. References [1] Fritts, D. C.; Alexander, M. J. Gravity wave dynamics and effects in the middle atmosphere. Reviews of geophysics, 2003, 41.1. [2] Gilli, G., et al. Impact of gravity waves on the middle atmosphere of Mars: A non‐orographic gravity wave parameterization based on global climate modeling and MCS observations. Journal of Geophysical Research: Planets, 2020, 125.3: e2018JE005873. [3] Brasil, Francisco, et al. Characterising Atmospheric Gravity Waves on Mars using Mars Express OMEGA images–a preliminary study. In: European Planetary Science Congress. 2021. p. EPSC2021-188. [4] Bibring, J. P., et al. OMEGA: Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité. In: Mars Express: the scientific payload. 2004. p. 37-49. [5] Chicarro, A.; Martin, P.; Trautner, R. The Mars Express mission: an overview. In: Mars Express: The Scientific Payload. 2004. p. 3-13.

<p>Aqueous alteration minerals are high-value scientific targets and potential resources for future exploration. In particular, they are key drivers in the selection of contemporary and upcoming landing sites at Mars. Here we report on the “MOCAAS” (<em>Mars Orbital Catalog of Aqueous Alteration Signatures</em>) project, a 10-year endeavor which built a comprehensive high-resolution repository of aqueous minerals on Mars. Our project goals include: 1) providing a statistically meaningful global approach to aqueous minerals, 2) providing regional mineralogical context to better understand specific sites of interest, 3) identifying new high-science merit aqueous alteration mineral deposits, including as prospective landing sites, 4) providing groundwork for upcoming quantification work on the global inventory of volatiles sequestered in such minerals. A corollary are identifying sites which abundant aqueous alteration minerals provide ISRU opportunities for future human exploration.</p> <p>We will present the first global-scale analyses of our detection sample, our benchmark of the methodology on rover landing sites, and discuss limitations, biases and perspectives.</p> <p>We processed a large fraction of the OMEGA/Mars Express and CRISM/MRO datasets [Bibring+04; Murchie+07] which both allow retrieval of Mars surface reflectance in the [1.1-2.65] µm range used in this study. Their processing is described in [Carter+22] and yields aqueous alteration mineral detection (AMD) all over Mars. An AMD is a cluster of (nearly) contiguous pixels which we ascertained to contain similar spectral rationale for one or several aqueous minerals, to the sensibility limit of orbital near-infrared spectroscopy and observation spatial sampling. We combine several approaches that are systematic and semi-automatic as well as more refined manual investigations of individual observations from OMEGA and CRISM. Only confirmed AMDs are retained in the end which spectral content has been visually validated. We then further classify AMDs into 5 spectral-mineral classes: 1) Fe/Mg phyllosilicate clay, 2) Hydrous aluminosilicates and hydrated silica, 3) Poly/Semi-hydrated sulfate salts, 4) Mono-hydrated sulfate salts, and 5) Carbonates. These classes account for degeneracies in the diagnostic spectral features which cannot always be uniquely attributed to a given alteration mineral.</p> <p>Excluding polar latitudes, a large fraction of the Mars surface mineralogy has been surveyed at a sampling down to 200 m/pixel (>62% of the surface) using semi-automatic algorithms, and its near entirety at kilometric resolution. Candidate AMDs were then further investigated in detail at all resolutions. The total fraction of AMDs reported at Mars is ~1%, yet this fraction includes many terrains that exhibit surface dust, poor observational conditions, and are younger than the late Hesperian. Figure 1 provides the global distribution color-coding for spectral mineral classes which is seen to strongly correlate with the oldest, dust-poor terrains of Mars.</p> <p><img src="" alt="" width="1055" height="415" /></p> <p><em>Figure 1: Distribution of aqueous alteration mineral detections based on the OMEGA and CRISM datasets. Each color codes for the spectral mineral classes (Red: Fe/Mg phyllosilicates; Green-blue: sulfate salts; Orange: carbonates; Cyan: aluminosilicates or hydrated silica). Each color pixel here indicates that alteration minerals are present within a 4x4km² area. </em></p> <p>Preliminary analyses of the global distribution of aqueous alteration minerals will be presented, investigating distribution as a function of latitude, altitude, unit type and unit age. An example histogram of the distribution of aqueous minerals as a function of unit age is shown in Figure 2. In particular, we report the much more widespread occurrence of several types of aqueous minerals throughout the Noachian highlands of Mars compared to what was previously known.</p> <p><img src="" alt="" width="859" height="385" /></p> <p><em>Figure 2: preliminary statistics on the distribution of alteration minerals, as a function of their unit-age from [Tanaka+14].</em></p> <p>Our detection capability is then benchmarked by implementing the same mapping procedure but applied to well-studied candidate or current landing sites for rover missions: at Gale crater, Jezero Crater, Mawrth Vallis plateaus and Oxia Planum. For these, we generate local high resolution maps, for which an example is given at Jezero crater below.</p> <p><img src="" alt="" width="1029" height="763" /></p> <p><em>Figure 3: High resolution aqueous alteration mineral mapping of the surroundings of Mars 2020 in Jezero crater.</em></p> <p>We will discuss perspectives for both global analyses of aqueous minerals made possible by this catalogue (e.g. [Riu+22]), as well as regarding future studies of newly identified sites of interest for which we will present a sample.</p> <p>In the near-term, the MOCAAS catalogue of aqueous alteration minerals will be made available on the PSUP portal (psup.ias.u-psud.fr) as well as through a dedicated web portal.</p> <p>References: [Bibring+04] J.-P. Bibring et al., ESA Spec. Pub, 2004, https://ui.adsabs.harvard.edu/abs/2004ESASP1240...37B; [Murchie+07] S. Murchie et al., JGR, 2007, 10.1029/2006JE002682 ; [Carter+22] J. Carter et al., Icarus, <em>under revision</em> ; [Tanaka+14] K. Tanaka et al., 2014, http://pubs.er.usgs.gov/publication/sim3292 ; [Riu+22] L. Riu et al., <em>this conference</em>.</p>

A Martian water-ice cloud climatology has been extracted from OMEGA data covering 7 Martian years (MY 26-32) on the dayside. We derived two products, the Reversed Ice Cloud Index (ICIR) and the Percentage of Cloudy Pixels (PCP), indicating the mean cloud thickness and nebulosity over a regular grid (1 degrees longitude x 1 degrees latitude x 1 degrees Ls x 1 h Local Time). The ICIR has been shown to be a proxy of the water-ice column derived from the Mars Climate Database. The PCP confirms the existence and location of the main cloud structures mapped with the ICIR, but also gives a more accurate image of the cloud cover. We observed a more dense cloud coverage over Hellas Planitia, the Lunae Planum region and over large volcanoes (Tharsis volcanoes, Olympus and Elysium Montes) in the aphelion belt. For the first time, thanks to the fact that Mars Express is not in Sun-synchronous orbit, we can explore the clouds diurnal cycle at a given season by combining the seven years of observations. However, because of the eccentric orbit, the temporal coverage remains limited. Identified limitations of the dataset are its small size, the difficult distinction between ice clouds and frosts, and the impact of surface albedo on data uncertainty. We could nevertheless study the diurnal cloud life cycle by averaging the data over larger regions: from specific topographic features (covering a few degrees in longitude and latitude) up to large climatic bands (covering all longitudes). We found that in the tropics (25 degrees S - 25 degrees N) around northern summer solstice, the diurnal thermal tide modulates the abundance of clouds, which is reduced around noon (Local Time). At northern midlatitudes (35 degrees N - 55 degrees N), clouds corresponding to the edge of the north polar hood are observed mainly in the morning and around noon during northern winter (Ls = 260 degrees-30 degrees). Over Chryse Planitia, low lying morning fogs dissipate earlier and earlier in the afternoon during northern winter. Over Argyre, clouds are present over all daytime during two periods, around Ls = 30 degrees and 160 degrees.

We present a non-local thermodynamic equilibrium retrieval scheme for atmospheric composition and its application to Mars CO2 infrared limb emissions as measured by the OMEGA instrument on board Mars Express (MEx). These emissions are caused by CO2 fluorescence of solar radiation, and thus the retrieval scheme accounts for non-LTE processes. We analyzed the dayside limb observations from a selection of three OMEGA orbits or data qubes. Before the retrieval was applied, we performed a radiometric calibration, cleaned the spectra (including clustering techniques) and generated radiance vertical profiles for each dataset. We also present information on the inversion set up, results on the retrieved CO2 density profiles, as well as the temperature profiles derived from the CO2 densities by assuming hydrostatic equilibrium. An extensive sensitivity study of the retrieval scheme was carried out, including its application to the OMEGA spectra taken at different MEx orbital configurations, to conclude on its performance and to offer recommendations for its systematic use with MEx datasets. The uncertainty due to the instrumental Gain calibration and that caused by the retrieval noise error itself are of large importance for the inversion, but a comparable component of the total error comes from the uncertainties of the temperature provided by the GCM. We demonstrated that, between 120 and 160 km, CO2 profiles can be derived with a precision around 30% and a vertical resolution of about 15 km.

The imaging spectrometer OMEGA [1] operates in the VIS-NIR range, covering the (0.35 µm to 5.1 µm) range in 352 contiguous spectral channels. This spectral range has been chosen as it includes diagnostic signatures of most surface mafic and hydrated minerals, frosts and ices. With a 1.2 mrad IFOV, the footprint varies from 40 m when imaging from 40 kms, up to 4.8 km from an altitude of 4000 km: this allows a global spectral coverage of Phobos to be achieved, at various spatial resolution.Along its 16 years of orbital operations, Mars Express has performed tens of close flybys of Phobos, at altitudes down to ~ 50 kms. OMEGA has acquired unprecedented compositional data sets, in both the visible and the near-infrared spectral range. We shall present and discuss these observations, as witnesses of Phobos origin, with their relevance to the upcoming MMX JAXA mission.

Cross crater is a 65 km impact crater, located in the Noachian highlands of the Terra Sirenum region of Mars (30 degrees S, 158 degrees W), which hosts aluminum phyllosilicate deposits first detected by the Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitie (OMEGA) imaging spectrometer on Mars Express. Using high-resolution data from the Mars Reconnaissance Orbiter, we examine Cross crater's basin-filling sedimentary deposits. Visible/shortwave infrared (VSWIR) spectra from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions diagnostic of alunite. Combining spectral data with high-resolution images, we map a large (10 km x 5 km) alunite-bearing deposit in southwest Cross crater, widespread kaolin-bearing sediments with variable amounts of alunite that are layered in <10 m scale beds, and silica- and/or montmorillonite-bearing deposits that occupy topographically lower, heavily fractured units. The secondary minerals are found at elevations ranging from 700 to 1550 m, forming a discontinuous ring along the crater wall beneath darker capping materials. The mineralogy inside Cross crater is different from that of the surrounding terrains and other martian basins, where Fe/Mg-phyllosilicates and Ca/Mg-sulfates are commonly found. Alunite in Cross crater indicates acidic, sulfurous waters at the time of its formation. Waters in Cross crater were likely supplied by regionally upwelling groundwaters as well as through an inlet valley from a small adjacent depression to the east, perhaps occasionally forming a lake or series of shallow playa lakes in the closed basin. Like nearby Columbus crater, Cross crater exhibits evidence for acid sulfate alteration, but the alteration in Cross is more extensive/complete. The large but localized occurrence of alunite suggests a localized, high-volume source of acidic waters or vapors, possibly supplied by sulfurous (H2S- and/or SO2-bearing) waters in contact with a magmatic source, upwelling steam or fluids through fracture zones. The unique, highly aluminous nature of the Cross crater deposits relative to other martian acid sulfate deposits indicates acid waters, high water throughput during alteration, atypically glassy and/or felsic materials, or a combination of these conditions.

Here we discuss one of the current reservoirs of water on Mars, the regolith and rocks exposed at the surface. This reservoir is characterized by the presence of H_{2}O- and OH- bearing phases that produce a broad absorption at a wavelength of \sim 3 \mu m in near-infrared (NIR) reflectance spectra. This absorption is present in every ice-free spectrum of the Martian surface obtained thus far by orbital NIR spectrometers. We present a quantitative analysis of the global distribution of the 3 \mu m absorption using the Observatoire pour la Min\'eralogie, l\'\Eau, les Glaces et l\'\Activit\'e (OMEGA) imaging spectrometer that has been mapping the surface of Mars at kilometer scale for more than ten years. Based on laboratory reflectance spectra of a wide range of hydrous minerals and phases, we estimate a model-dependent water content of 4\pm 1 wt. \% in the equatorial and mid-latitudes. Surface hydration increases with latitude, with an asymmetry in water content between the northern and southern hemispheres. The surface hydration is compared to various parameters (albedo, dust, geological units, time, relative humidity, atmospheric water pressure, and in situ measurements performed by Phoenix and Curiosity) to constrain the nature of the reservoir. We conclude that the nature of the surface hydration of the Martian low latitudes is not adsorbed water but rather more tightly-bound water molecules and hydroxyl groups in the structure of the materials of the near-top surface. A frost-related process best explains the implementation of water into and onto the first microns of the high latitudes Martian regolith.

Stable isotope ratios of H, C, and O are powerful indicators of a wide variety of planetary geophysical processes, and for Mars they reveal the record of loss of its atmosphere and subsequent interactions with its surface such as carbonate formation. We report in situ measurements of the isotopic ratios of D/H and (18)O/(16)O in water and (13)C/(12)C, (18)O/(16)O, (17)O/(16)O, and (13)C(18)O/(12)C(16)O in carbon dioxide, made in the martian atmosphere at Gale Crater from the Curiosity rover using the Sample Analysis at Mars (SAM)'s tunable laser spectrometer (TLS). Comparison between our measurements in the modern atmosphere and those of martian meteorites such as ALH 84001 implies that the martian reservoirs of CO2 and H2O were largely established ~4 billion years ago, but that atmospheric loss or surface interaction may be still ongoing.

Several hundred occurrences of chloride‐bearing salt deposits have been proposed in terrains within the southern highlands of Mars on the basis ofThermal Emission Imaging System and Thermal Emission Spectrometerinfrared observations. The spectral identification of chloride salts by remote sensing is challenging because they are transparent over much of the thermal infrared portion of the spectrum. Further ambiguity arises from the diverse geologic settings in which the putative chloride‐bearing materials are found. In order to better constrain the composition of these unique compositional units, we perform a global survey of these materials in the Near‐Infrared (NIR) domain with theObservatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité(OMEGA) imaging spectrometer. The spectral signatures of the deposits are consistent with – although not specific of – chlorides. We do not observe olivine to be associated with the deposits, which confirms that sulfides are an unlikely alternative candidate. Our systematic search reveals the global lack of association with hydrated minerals (phyllosilicates, sulfates, hydrated silica) except for a few deposits (noteworthy in northwestern Terra Sirenum) where a small fraction of chloride material overlaps Fe/Mg‐rich clay‐bearing terrains. Even in these locations, the morphology and crosscutting relationships of the deposits suggest two separate episodes of mineralization, first phyllosilicates then chlorides, followed by subsequent formation of sulfates. Our study shows that local groundwater upwelling seems to be the most frequent source for the water involved in the formation of chloride, rather than surface runoff.

clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles ): September 7, 2012 www.sciencemag.org (this information is current as of The following resources related to this article are available online at http://www.sciencemag.org/content/312/5772/400.full.html version of this article at: including high-resolution figures, can be found in the online Updated information and services, 245 article(s) on the ISI Web of Science cited by This article has been http://www.sciencemag.org/content/312/5772/400.full.html#related-urls 26 articles hosted by HighWire Press; see: cited by This article has been http://www.sciencemag.org/cgi/collection/planet_sci Planetary Science subject collections: This article appears in the following

Carbon dioxide clouds, which are speculated by models on solar and extra-solar planets, have been recently observed near the equator of Mars. The most comprehensive identification of Martian CO2 ice clouds has been obtained by the near-IR imaging spectrometer OMEGA. CRISM, a similar instrument with a higher spatial resolution, cannot detect these clouds with the same method due to its shorter wavelength range. Here we present a new method to detect CO2 clouds using near-IR data based on the comparison of H2O and CO2 ice spectral properties. The spatial and seasonal distributions of 54 CRISM observations containing CO2 clouds are reported, in addition to 17 new OMEGA observations. CRISM CO2 clouds are characterized by grain size in the 0.5-2\mum range and optical depths lower than 0.3. The distributions of CO2 clouds inferred from OMEGA and CRISM are consistent with each other and match at first order the distribution of high altitude (>60km) clouds derived from previous studies. At second order, discrepancies are observed. We report the identification of H2O clouds extending up to 80 km altitude, which could explain part of these discrepancies: both CO2 and H2O clouds can exist at high, mesospheric altitudes. CRISM observations of afternoon CO2 clouds display morphologies resembling terrestrial cirrus, which generalizes a previous result to the whole equatorial clouds season. Finally, we show that morning OMEGA observations have been previously misinterpreted as evidence for cumuliform, and hence potentially convective, CO2 clouds.

We used Mars Express HRSC and OMEGA data to investigate mesospheric cloud features observed in the equatorial belt of Mars from December 2007 until early March 2008. This period corresponds to early northern spring of Martian year 29. The reflection peak at 4.26μm in OMEGA data identifies the clouds as CO2 ice clouds. HRSC observed the clouds together with OMEGA in five orbits. Cloud features are most prominent in the shortwave HRSC colour channels with wavelength centers at 440 and 530nm, but rarely visible in all other channels. In the period of Ls 0–36°, OMEGA and HRSC together detected mesospheric CO2 ice clouds in 40 orbits. They occur in a latitude belt of ±20° around the equator and at longitudes between 240°E (Tharsis) in the West and 30°E (Sinus Meridiani) in the East. The clouds were observed between 3 and 5 p.m. local time with mainly ripple-like to filamentary cloud forms. The viewing angles of the HRSC blue and green colour channels differ by 6.6° and the resulting parallax can be used to directly measure cloud heights by means of ray intersection. 17 HRSC data takes were found to exhibit clouds with heights from 66 to 83km with an accuracy of 1–2km. The pushbroom imaging technique also yields a time delay for the two observations in the order of 5–15s close to periapsis, and therefore time-related cloud movements can be detected. A method was developed to determine the across-track cloud displacements, which can directly be translated to wind velocities. Zonal cloud movements could be measured in 13 cases and were oriented from East to West. Related wind speeds range between 60 and 93m/s with an accuracy of 10–13m/s.

. clicking here colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others . here following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles (this information is current as of August 21, 2010 ): The following resources related to this article are available online at www.sciencemag.org http://www.sciencemag.org/cgi/content/full/312/5772/400 version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/cgi/content/full/312/5772/400#otherarticles , 10 of which can be accessed for free: cites 31 articles This article 230 article(s) on the ISI Web of Science. cited by This article has been http://www.sciencemag.org/cgi/content/full/312/5772/400#otherarticles 23 articles hosted by HighWire Press; see: cited by This article has been http://www.sciencemag.org/cgi/collection/planet_sci Planetary Science : subject collections This article appears in the following

The Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument is a visible and near-infrared imaging spectrometer on board the European Mars Express (MEx) mission. The on-board calibration (OBC) performed at the beginning of observations on each orbit reveals that the photometric response of the C channel (1.0–2.5 μm) has been very stable since orbit insertion in January 2004. On the contrary the L channel (2.5–5.1 μm) response has varied significantly during the mission, and only orbits for which the response is close to nominal could be used with confidence. The spatial coverage of ice-free surfaces in this wavelength range is consequently limited to only ∼30%, mainly during northern spring and summer. This paper presents the empirical method used to derive new instrumental transfer functions (ITF) for the non-nominal orbits. This method consists of analyzing the variation of the signal between several observations of a same region acquired at nominal and non-nominal calibration states. In the cases where the mineralogy and the atmospheric conditions between the two observations are the same, the variation in reflectance spectra is only due to the ITF variation, which provides a new ITF. We then associate these new ITFs with their corresponding OBCs to model a relationship between both. The resulting model enables us to provide a new ITF for each orbit for which the OBC is available. The new ITFs derived for the entire dataset have been validated (1) through a comparison of the C and L channel global albedo trends and (2) through a comparison of the surface temperatures derived from the L channel with those calculated from the General Circulation Model (GCM) numerical simulation of the LMD released in the Martian Climate Database. The non-nominal data processed with adapted ITFs for orbits up to 3050 increase the non-icy surface coverage of Mars to ∼70% including all seasons.

Sulfates have been discovered by the OMEGA spectrometer in different locations of the planet Mars. They are strongly correlated to light toned layered deposits in the equatorial regions. West Candor Chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates. A detailed study coupling mineralogy derived from OMEGA spectral data and geology derived from HRSC imager and other datasets leads to some straightforward issues. The monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material. It likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments, or during hydrothermal alteration at depth, because it is typically found on outcrops that are eroded and steep. Polyhydrated sulfates, that match any Ca-, Na-, Fe-, or Mg-sulfates with more than one water molecule, are preferentially present on less eroded and darker outcrops than outcrops of kieserite. These variations can be the result of a diversity in the composition and/or of the rehydration of kieserite on surfaces with longer exposure. The latter possibility of rehydration in the current, or recent, atmosphere suggests the low surface temperatures preserve sulfates from desiccation, and, also can rehydrate part of them. Strong signatures of iron oxides are present on sulfate-rich scarps and at the base of layered deposits scarps. They are correlated with TES gray hematite signature and might correspond to iron oxides present in the rock as sand-size grains, or possibly larger concretions, that are eroded and transported down by gravity at the base of the scarp. Pyroxenes are present mainly on sand dunes in the low lying terrains. Pyroxene is strongly depleted or absent in the layered deposits. When mixed with kieserite, local observations favor a spatial mixing with dunes over layered deposits. Sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation, either in an intermittent lacustrine environment or by hydrothermal fluid circulation. Both possibilities require the presence of sulfur-rich groundwater to explain fluid circulation. The elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2.5 km above datum, only 1 km below the plateau surface.

Visible‐near infrared reflectance spectra acquired by the Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) spectrometer are used to estimate the absolute water content within the uppermost fraction of the Martian regolith. This upper surface layer represents the boundary between the regolith and atmosphere; thus the amount of water stored in these two reservoirs and at this boundary is expected to vary spatially and temporally with changing equilibrium conditions. We have applied models derived from laboratory experiments relating the strength of the 3 μ m hydration feature to absolute water content to OMEGA spectra acquired during the first ∼1200 orbits of the Mars Express mission to estimate the H 2 O content of the Martian surface. Three methods were used to examine the strength of the 3 μ m absorption: integrated band depth, apparent absorbance, and the effective single‐particle absorption‐thickness (ESPAT) parameter. Integrated band depth and apparent absorbance values are correlated to albedo when derived from reflectance spectra, implying that bright regions are more hydrated than dark regions. The ESPAT parameter, however, relies on single scattering albedo instead of reflectance and is capable of estimating absolute water content within ±1 wt.% H 2 O for a wide range of albedo values, compositions, and particle sizes. Applying this model to the OMEGA data reveals that bright and dark regions commonly have similar water contents in equatorial regions and the largest spatial variations in H 2 O occur as a function of latitude. Equatorial regions exhibit water contents in the range of ∼2–5 wt.%, whereas latitudes higher than ∼45°N are characterized by a continuous increase in H 2 O with latitude from ∼5–15 wt.%. Phyllosilicate and sulfate bearing terrains are more hydrated than average bright and dark regions and their locations are in widely separated areas of Noachian‐aged material, suggesting chemical alteration by water‐rock interaction may have been spatially extensive in the early history of Mars.