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In the past two decades, near-infrared (NIR) hyperspectral imaging instruments have revolutionized our conception of planetary surfaces in terms of evolution, geology, mineralogy, and alteration processes. The cornerstone of this remote analysis technique is the synergy between imagery, giving the geomorphological context of the observations, and NIR spectroscopy whose spectral range is sensitive to the main absorption features of most of the minerals present on planetary surfaces. The development of a generation of space instrument based on Acousto-Optic Tunable Filters (AOTFs) increases the capacity of these spectrometers to be set up in a variety of space probes. The ExoCam concept, developed at Institut d’Astrophysique Spatiale and profiting from the lab’s previous experience (MicrOmega onboard Phobos-Grunt, Hayabusa 2 and ExoMars), thus, proposes for the first time to do hyperspectral imagery through a wide aperture AOTF (15 × 15 mm2) in the 0.95–3.6 µm spectral range. The characterization of this instrumental concept, led on a representative breadboard built for this purpose, showed that the acousto-optic diffraction preserves the image quality up to the diffraction/resolution limit over the whole field of view. The spectral resolution (from 2 to 25 nm over the spectral range) and accuracy of the instrument are also consistent with the identification of planetary surface minerals. This paper describes the ExoCam concept and objectives, the setup of an optical breadboard representative of a space instrument based on this concept, and the results of performance characterizations realized on the breadboard.

著者人数: 66名 (所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 岩田, 隆浩; 安部, 正真; 大竹, 真紀子; 仲内, 悠佑; 松岡, 萌; L. Riu; 中藤, 亜衣子; 横田, 康弘; 坂谷, 尚哉; 山本, 幸生; 岡田, 達明; 澤田, 弘崇, 早川, 雅彦; 白井, 慶; 嶌生, 有理; 尾川, 順子; 照井, 冬人; 竹井, 洋; 佐伯, 孝尚; 中澤, 暁; 田中, 智; 吉川, 真; 渡邊, 誠一郎; 津田, 雄一), Accepted: 2019-03-07, 資料番号: SA1180385000

著者人数: 60名 (所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 渡邊, 誠一郎; 野口, 里奈; 嶌生, 有理; 吉川, 真; 菊地, 翔太; 橘, 省吾; 石原, 吉明; 坂谷, 尚哉; 竹内, 央; 岡田, 達明; 安部, 正真; 山本, 幸生; 田中, 智; 白井, 慶; 松岡, 萌; 横田, 康弘; 山口, 智宏; 尾川, 順子; 三桝, 裕也; 高橋, 忠輝; 竹井, 洋; 藤井, 淳; 岩田, 隆浩; 早川, 雅彦; 細田, 聡史; 森, 治; 澤田, 弘崇; 嶋田, 貴信; Soldini, Stefania; 矢野, 創; 月崎, 竜童; 尾崎, 正伸; 飯島, 祐一; 藤本, 正樹; 照井, 冬人; 佐伯, 孝尚; 中澤, 暁; 津田, 雄一), Accepted: 2019-03-07, 資料番号: SA1180386000

Analyses of meteorites and theoretical models indicate that some carbonaceous near-Earth asteroids may have been thermally altered due to radiative heating during close approaches to the Sun1–3. However, the lack of direct measurements on the subsurface doesn’t allow us to distinguish thermal alteration due to radiative heating from parent-body processes. In April 2019, the Hayabusa2 mission successfully completed an artificial impact experiment on the carbonaceous near-Earth asteroid (162173) Ryugu4,5, which provided an opportunity to investigate exposed subsurface material and test potential effects of radiative heating. Here we report observations of Ryugu’s subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. The strength and shape of the OH feature suggests that the subsurface material experienced heating above 300 °C, similar to the surface. In contrast, thermophysical modelling indicates that radiative heating cannot increase the temperature above 200 °C at the estimated excavation depth of 1 m, even at the smallest heliocentric distance possible for Ryugu. This supports the hypothesis that primary thermal alteration occurred on Ryugu’s parent body. Hayabusa2 created an artificial crater on Ryugu to analyse the subsurficial material of the asteroid. Results show that the subsurface is more hydrated than the surface. It experienced alteration processes that can be traced back to Ryugu’s parent body.

A radiative transfer model was used to reproduce several millions of OMEGA (Observatoire pour la Min\'eralogie, l'Eau, les Glaces et l'Activit\'e) spectra representative of igneous terrains of Mars. This task provided the modal composition and grain sizes at a planetary scale. The lithology can be summarized in five mineral maps at km-scale. We found that the low albedo equatorial regions of the Martian surface (from 60{\deg}S to 30{\deg}N) are globally dominated by plagioclase with average abundance ~50 vol% and pyroxenes with total averaged abundance close to 40 vol%. An evolution of the LCP/(LCP+HCP) ratio is observed with time at the global scale, suggesting an evolution of the degree of partial melting throughout the Martian eras. Olivine and Martian dust are minor components of the modelled terrains. The olivine distribution is quite different from the other minerals because it is found on localized areas with abundance reaching 20 vol%. A statistical approach, to classify the pixels of the abundances maps, using k-means clustering, highlighted seven distinct mineral assemblages on the surface. This classification illustrates that diverse mineralogical units are found in the Noachian and Hesperian terrains, which suggests the presence of various and complex magmatic processes at a global scale during the two oldest eras. The chemical composition was derived from the modal composition maps. The OMEGA-derived chemical composition is quite consistent with several distinctive geochemical characteristics previously considered as fingerprints of the Martian surface. A major discrepancy is in regards to the Fe content that is significantly smaller than soil and rock analyses from GRS and in situ measurements. The discrepancy could be partly explained by the assumptions used for the spectral modelling or could also indicate surface alteration rinds.

International audience; Multiple spectroscopic techniques have been selected on previous, present and forthcoming missions to explore planetary surfaces in the Solar System. In particular, forthcoming ESA/Roscosmos and NASA missions to the surface of Mars will bring instruments capable of near-infrared (NIR), Raman and Laser Induced Breakdown Spectroscopies to analyze the mineralogy and chemistry of rocks. The PTAL (Planetary Terrestrial Analogues Library) project aims at building a multi-instrument spectral database of a large variety of natural Earth rock samples, including Mars analogues. The NIR hyperspectral microscope MicrOmega was selected to characterize the mineralogy of these analogues within the PTAL project. The instrument model used for the PTAL project is a spare flight model that requires specific care. For the safety of the instrument, and because of the large number of samples in the PTAL library and the requirement to optimize the observational conditions, a dedicated and semiautomated setup was built for the use of the MicrOmega instrument for this project. This paper presents the requirements specified for this setup, the technical solutions that have been selected, their implementation and the performances of the setup. Sample preparation and operations during sample observations are explained, and a characterization example is presented to briefly illustrate the capabilities of MicrOmega in this setup. The complete results from the MicrOmega characterizations of the PTAL rock analogues will be presented in a forthcoming paper (Loizeau et al. in prep).

We extracted a Martian water-ice cloud climatology from OMEGA data covering 7 Martian years (MY 26-32). 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{\deg} longitude x 1{\deg} latitude x 1{\deg} 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 location of the main cloud structures mapped with the ICIR, and gives a more accurate image of the cloud cover. We observed a denser cloud coverage over Hellas Planitia, Lunae Planum and over large volcanoes 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 cloud diurnal cycle at a given season by combining 7 years of observations. However, because of the eccentric orbit, the temporal coverage remains limited. Other 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 (all longitudes). We found that in the tropics around northern summer solstice, the diurnal thermal tide modulates the abundance of clouds, which is reduced around noon. At northern midlatitudes, clouds corresponding to the edge of the north polar hood are observed mainly in the morning and around noon during northern winter (Ls=260-30{\deg}). 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 and 160{\deg}., Comment: PDF, 55 pages, 22 figures, 2 tables. Accepted article (journal : Icarus)

This paper is the first paper of a series that will present the derivation of the modal mineralogy of Mars (M3 project) at a global scale from the near-infrared dataset acquired by the imaging spectrometer OMEGA (Observatoire pour la Min\'eralogie, l'Eau, les Glaces et l'Activit\'e) on board ESA/Mars Express. The objective is to create and provide a global 3-D image-cube of Mars at 32px/{\deg} covering most of Mars surface. This product has several advantages. First, it can be used to instantaneously extract atmospheric- and aerosol-corrected near-infrared (NIR) spectra from any location on Mars. Second, several new data maps can be built as discussed here. That includes new global mineral distributions, quantitative mineral abundance distributions and maps of Martian surface chemistry (wt % oxide) detailed in a companion paper (Riu et al., submitted). Here we present the method to derive the global hyperspectral cube from several hundred millions of spectra. Global maps of some mafic minerals are then shown, and compared to previous works.

On the 12th of November 2014, the Rosetta Philae Lander descended to make the first soft touchdown on the surface of a comet – comet 67P/Churyumov- Gerasimenko. That soft touchdown did occur but due to the failure in the firing of its two harpoons, Philae bounced and travelled across the comet making contact with the surface twice more before finally landing in a shaded rocky location somewhere on the southern hemisphere of the comet. The search campaign, led by ESA, involved multiple teams across Europe with a wide range of techniques used in support of it. This search campaign would continue through 2015 where a prime candidate on the surface was identified and on into 2016 to end on the 2nd of September 2016 when a definitive and conclusive image was taken of the lander on the surface of the comet, confirming the prime candidate to indeed be Philae.

The Mawrth Vallis region is covered by some of the largest phyllosilicate-rich outcrops on Mars, making it a unique window into the past history of Mars in terms of water alteration, potential habitability, and the search for past life. A landing ellipse had been proposed for the Curiosity rover. This area has been extensively observed by the High Resolution Imaging Science Experiment and the Compact Reconnaissance Imaging Spectrometer for Mars, offering the possibility to produce geologic, structural, and topographic maps at very high resolution. These observations provide an unprecedented detailed context of the rocks at Mawrth Vallis, in terms of deposition, alteration, erosion, and mechanical constraints. Our analyses demonstrate the presence of a variety of alteration environments on the surface and readily accessible to a rover, the presence of flowing water at the surface postdating the formation of the clay-rich units, and evidence for probable circulation of fluids in the rocks at different depths. These rocks undergo continuous erosion, creating fresh outcrops where potential biomarkers may have been preserved. The diversity of aqueous environments over geological time coupled to excellent preservation properties make the area a very strong candidate for future robotic investigation on Mars, like the NASA Mars 2020 mission.

The objective of this study is to identify and map spectral analogues of some key martian meteorites (basaltic shergottites Los Angeles, Shergotty, QUE 94201, lherzolitic shergottite ALH A77005, Nakhla, Chassigny and the orthopyroxenite ALH 84001) in order to localize terrain candidates for their source regions. We develop a best fit procedure to reproduce the near-infrared (NIR) spectral properties of the martian surface as seen by the hyperspectral imaging spectrometer OMEGA/MEx from the NIR spectra of the martian meteorites. The fitting process is tested and validated, and Root Mean Square (RMS) global maps for each meteorite are obtained. It is found that basaltic shergottites have NIR spectral properties the most representative of the martian surface with the best spectral analogues found in early Hesperian volcanic provinces. Sites with spectral properties similar to those of ALH A77005 are scarce. They are mainly localized in olivine-bearing regions such as Nili Fossae and small Noachian/early Hesperian terrains. The only plausible source region candidate for Chassigny is the Nili Patera caldera dated to 1.6 Ga. Widespread spectral analogues for the ALH 84001 meteorite are found northeast of Syrtis Major and northwest of the Hellas basin. While this distribution is in agreement with the low-calcium-pyroxene-rich composition and old age (4.1 Ga) of this meteorite, the modal mineralogy of these candidates is not consistent with that of this meteorite. No convincing spectral analogue is found for the Amazonian-aged Nakhla meteorite suggesting that its olivine/high-calcium-pyroxene-rich composition could be representative of the Amazonian terrains buried under dust. Finally, some young rayed craters are proposed as possible candidates for source craters of the studied martian meteorites.

MicrOmega is an NIR hyperspectral microscope that has been selected as part of the ExoMars rover payload. We demonstrate here that this instrument has the capability through automated algorithms to identify and locate grains of interest (composition-wise) within a collected sample that could be further targeted by other instruments within the ExoMars payload. Results will also be used to perform an optimized compression of the data, with regard to the relevance of the different grains, in order to limit the volume of downloaded data. The algorithms that we have developed, using combined spectral criteria and different tests to avoid false positive, have proven to be both highly robust and efficient. They will be used onboard ExoMars rover, and could also be adapted for future robotic missions involving hyperspectral microscopes.

Hyperspectral microscopy, by its capability to characterize in situ the composition of samples at their grain size scale and the coupling between the different phases, complements efficiently the remote sensing hyperspectral imagers. Objectives, rationale and limits of hyperspectral microscopy in the planetary science field are summarized in this paper. A new concept of NIR reflectance hyperspectral microscope, MicrOmega is presented and results obtained both with a representative breadboard and a first version of the MicrOmega instrument, recently integrated on the Phobos Grunt lander, are discussed. Results show that we are now able to build instruments capable of analyzing samples at the grain scale, typically a few tens of microns per pixel, within volume, weight, power and time budgets compatible with typical rover’s constraints. We demonstrate the ability of such instruments to characterize samples, identify their major and minor constituents, some non-detectable from orbit, and their spatial coupling. Instruments based on the MicrOmega concept have been selected as part of the Hayabusa-2 Mascot Lander that will study in situ a C-class asteroid, as well as of the ExoMars rover that would characterize Mars potential past and present habitability. In both cases, these in situ analyses should provide essential data to improve our understanding of the history of the object explored.

By using the images acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) and ROLIS (ROsetta Lander Imaging System) cameras, we derive the size¿ frequency distribution (SFD) of cometary pebbles and boulders covering the size range 0.05¿ 30.0 m on the Agilkia landing site. The global SFD measured on OSIRIS images, reflects the different properties of the multiple morphological units present on Agilkia, combined with selection effects related to lifting, transport and redeposition. Contrarily, the different ROLIS SFD derived on the smooth and rough units may be related to their different regolith thickness present on Agilkia. In the thicker, smoother layer, ROLIS mainly measures the SFD of the airfall population which almost completely obliterates the signature of underlying boulders up to a size of the order of 1 m. This is well matched by the power-law index derived analysing coma particles identified by the grain analyser Grain Impact Analyser and Dust Accumulator. This result confirms the important blanketing dynamism of Agilkia. The steeper SFD observed in rough terrains from 0.4 to 2 m could point out intrinsic differences between northern and southern dust size distributions, or it may suggest that the underlying boulders `peek through¿ the thinner airfall layer in the rough terrain, thereby producing the observed excess in the decimetre size range. Eventually, the OSIRIS SFD performed on the Philae landing unit may be due to water sublimation from a static population of boulders, affecting smaller boulders before the bigger ones, thus shallowing the original SFD., The support of the national funding agencies of Germany (DLR), France(CNES), Italy(ASI), Spain(MEC), Sweden(SNSB) and the ESA Technical Directorate is gratefully acknowledged.

We present a method to derive the 2D maps of the O 2 (a 1 Δ g ) airglow emission at 1.27 μm from the OMEGA/MEx nadir observations. The OMEGA imaging capabilities allow monitoring the 2D distribution, daily and seasonal variation of the O 2 emission intensities with a detection limit of 4 MR. The highest values, of the order of ∼31 MR, are found on the south pole for 11 h [Clancy, R.T., Wolff, M.J., Christensen, P.R., 2003. Mars aerosol studies with the MGS TES emission phase function observations: Optical depths, particle sizes, and ice cloud types versus latitude and solar longitude. J. Geophys. Res. 108. doi: 10.1029/2003JE002058] . In the polar regions the day-by-day variability, associated with polar vortex turbulences, is obtained of the order of 30–50% as predicted by the model [Lefevre, F., Lebonnois, S., Montmessin, F., Forget, F., 2004. Three-dimensional modeling of ozone on Mars. J. Geophys. Res. 109, E07004. doi: 10.1029/2004JE002268 ] and found by SPICAM [Perrier, S., Bertaux, J.-L., Lebonnois, S., Korablev, O., Fedorova, A., 2006. Global distribution of total ozone on Mars from SPICAM/MEX UV measurements. J. Geophys. Res. 111, E09S06. doi: 10.1029/2006JE002681 ]. In the considered set of data a maximum of the O 2 emission is observed between 11 h and 15 h LT in the latitude range 70–85° during early spring on both hemispheres, while for the southern autumn–winter season a maximum is found between 50° and 60° in the southern hemisphere for MY28. Increase of intensity of the O 2 emission observed from Ls 130° to 160° at southern high latitudes may be explained by increase of solar illumination conditions in the maps acquired during the considered period. Atmospheric waves crossing the terminator on the southern polar regions are observed for the first time during the MY28 early spring. The spatial scale of the waves ranges from 100 to 130 km, and the intensity fluctuations are of the order of 4MR. This study confirms the high potentiality of O 2 (a 1 Δ g ) day glow as a passive tracer of the martian atmosphere dynamics at high latitudes.

The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.

The structure and composition of cometary constituents, down to their microscopic scale, are critical witnesses of the processes and ingredients that drove the formation and evolution of planetary bodies toward their present diversity. On board Rosetta's lander Philae, the Comet Infrared and Visible Analyser (CIVA) experiment took a series of images to characterize the surface materials surrounding the lander on comet 67P/Churyumov-Gerasimenko. Images were collected twice: just after touchdown, and after Philae finally came to rest, where it acquired a full panorama. These images reveal a fractured surface with complex structure and a variety of grain scales and albedos, possibly constituting pristine cometary material.

The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle “splashing” is responsible for the observed formations.

International audience; The structure and composition of cometary constituents, down to their microscopic scale, are critical witnesses of the processes and ingredients that drove the formation and evolution of planetary bodies toward their present diversity. On board Rosetta's lander Philae, the Comet Infrared and Visible Analyser (CIVA) experiment took a series of images to characterize the surface materials surrounding the lander on comet 67P/Churyumov-Gerasimenko. Images were collected twice: just after touchdown, and after Philae finally came to rest, where it acquired a full panorama. These images reveal a fractured surface with complex structure and a variety of grain scales and albedos, possibly constituting pristine cometary material.

The area of Meridiani Planum on Mars became of particular interest after the detection of coarse-grained, gray hematite, which led to the choice of this region as final landing site for the Mars Exploration Rover Opportunity. Multiple additional minerals have since been detected in the region, both from orbit and in situ. The present paper reassesses in detail the mineralogy and geomorphology of the area (between 3.5°S to 6.5°N latitude and 8.0°W to 8.0°E longitude) using visible and near-infrared hyperspectral data, merged with high spatial resolution images into a Geographic Information System. Fe/Mg-rich phyllosilicates, as well as several types of sulfates are identified within the kilometer of sedimentary deposits constituting the etched terrains and the overlying hematite-rich plains. The mineralogical stratigraphy of the etched terrains is characterized by a sulfate-rich unit, enriched in Fe/Mg-rich clays in its uppermost part. This clay-rich horizon is capped by another sulfate-rich unit, of different composition, associated with hematite detections and constituting the material of the hematite plains unit. The clay-bearing unit, which directly underlies the hematite plains, may be exposed in the rim of Endeavour Crater and could correspond to the material that is currently being analyzed by Opportunity. Diverse landforms including karsts and pan features are observed at the surface of the hydrated etched terrains and indicate past surface water and potential groundwater aquifers. Our analysis reveals that both surficial water and groundwater processes are required to explain the diversity of morphologies and mineralogies observed in the area. Although orbital detections are consistent with the hematite and sulfate detections made in situ by Opportunity in the hematite plains, they also show the presence of a clay-rich horizon at depth, overlying another, thicker, possibly chemically distinct, sulfate-rich unit within the etched terrains. Therefore we conclude that the very acidic conditions that prevailed during the formation of the topmost sulfate-rich unit, as observed in Meridiani Planum and in the hematite plains by the rover Opportunity, are not representative of the entire history of the etched terrains. In contrast, most hydrated minerals in Meridiani Planum likely formed at more neutral pH, at the beginning of the Hesperian. The overall sulfate/clay/sulfate sequence is similar to the one observed in Gale Crater, the landing site of the Mars Science Laboratory rover.

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ(-1)), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

In this paper we discuss the on-ground and in-flight performances of the visual channel of the OMEGA instrument on board the European mission Mars Express. OMEGA is a mapping spectrometer designed for mineralogical and atmospheric investigation of Mars. This work aims to be a guide to future users for the analysis of the OMEGA data. We give a detailed description of the instrumental characteristics of the OMEGA visual channel and systematic effects known so far, providing the guideline for the correct data processing.

Being successfully launched on March 2, 2004, ESA’s cornerstone mission “ROSETTA” (originally planned to be launched in January 2003 to comet Wirtanen) is en route. It will also bring the 100 kg Lander “Philae” with a scientific payload of 26.7 kg to the surface of comet 67P/Churyumov-Gerasimenko. After a first scientific sequence in 2014 it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and at least 2 AU). The Lander, after separation, is an autonomous spacecraft powered with solar cells and using the ROSETTA Orbiter as a telemetry relais to Earth. The main scientific objectives are the in situ investigation of the chemical, elemental, isotopic and mineralogical composition of the comet, study of the physical properties of the surface material, analyze the internal structure of the nucleus, observe temporal variations (day/night cycle, approach to sun), study the relationship between the comet and the interplanetary matter and provide ground truth data for the Orbiter instruments. Ten experiments with a number of sub-experiments are foreseen to fulfil these objectives. Philae is operated (via ESOC) by the Lander Control Centre (LCC) at DLR and the Science Operations and Navigation Centre (SONC) at CNES. In this paper we present the flight status of the scientific instruments as it is known after in-orbit commissioning.

The recent identification of large deposits of sulphates by remote sensing and in situ observations has been considered evidence of the past presence of liquid water on Mars. Here we report the unambiguous detection of diverse phyllosilicates, a family of aqueous alteration products, on the basis of observations by the OMEGA imaging spectrometer on board the Mars Express spacecraft. These minerals are mainly associated with Noachian outcrops, which is consistent with an early active hydrological system, sustaining the long-term contact of igneous minerals with liquid water. We infer that the two main families of hydrated alteration products detected-phyllosilicates and sulphates--result from different formation processes. These occurred during two distinct climatic episodes: an early Noachian Mars, resulting in the formation of hydrated silicates, followed by a more acidic environment, in which sulphates formed.

International audience; The OMEGA imaging spectrometer aboard Mars Express has been used to map the water vapor abundance over the martian surface, from the analysis of the 2.6 mum band of H2O. As a preliminary result of this study, we present water vapor maps in the northern hemisphere at the time of the northern polar cap sublimation (Ls = 94-112 deg). The maps show a mean H2O mixing ratio of about 2-3× 10-4 at a latitude of 40N, and in the range of 5 × 10-4-10-3 at 60N-80N latitudes. The corresponding mean H2O column densities are about 25 pr-mum at 40N and between 40 and 60 pr-mum at 60N-80N, with uncertainties of about 30 percent. Our results are in agreement with previous results by MAWD/Viking and TES/MGS for latitudes up to 60N, but seem to indicate lower values at high latitude. However they are still globally consistent in view of our error bars.

International audience; The Mars Express mission was launched in June 2003 and was inserted into orbit around Mars in December 2003. Its main objective is to study the Mars' subsurface, surface, atmosphere and interaction with the solar wind. A secondary objective is to study the martian moons, in particular the largest one Phobos, thanks to a near polar and elliptical orbit which allows the spacecraft to perform close flybys about every five months. The Mars Express data not only consist of high-resolution 3D color images, but also astrometric images, spectra from 0.18 to 20 μm, radar echoes, Doppler signals from gravity experiments, and ion data. A new view of the moons has emerged from this data set, favoring now the idea that they are not captured asteroids, but rather the result of a re-accretion following a major impact on Mars. This unique set of data is available in the ESA Planetary Science Archive (PSA) and mirror imaged in the NASA Planetary Data System (PDS). This paper presents an overview of the Mars Express Phobos flybys, the specificities of their operations and the scientific achievements.

In the context of dust collections in space, the COMET experiment (Collecte en Orbite de Matiere ExtraTerrestre) was proposed in 1982 and has been accepted in 1985 in the framework of the Soviet-French space cooperation program. The idea of such an experiment was to install collectors inside hermetic boxes, to have these boxes mounted outside a space station, orbiting the Earth and to have the capability of chosing the date and duration of the collection. In February 94, it has been proposed to fly an improved version of this instrument, as part of the payload of the EUROMIR 95 mission. Renamed as the European Space Exposure Facility (ESEF), it carries experiments from several principal investigators (PIs). These experiments have been designed to analyse in real time some parameters of the encountered particles and to collect material, both of terrestrial and extraterrestrial origin, to be brought back to the Earth at the end of the mission. Three types of collecting material are used: high purity metals, foams and silica aerogels. All grains down to submicron sizes can be possibly identified by such a variety of collectors; the presence of very low density collectors, like the foams and silica aerogels, should permit the collection of grains least modified, one of the primary goals of this investigation. This paper refers to the description of the instrument and of the various experiments.

Observations of Mars with the infrared imaging spectrometer ISM on board the Phobos -2 spacecraft provided more than 40,000 spectra in the wavelength range 0.7–3.2 μm with a spatial resolution of about 20 km. These spectra bear features of both atmospheric and surface origin. Measurements in the water vapour bands near 1.9 and 2.6 μm along the flanks of huge Martian volcanoes provided the data on the H 2 O spatial variations above them. The retrieved mixing ratio was about 200 ppm above the volcanoes, which was about a factor of five higher than that found above the surrounding terrains. The origin of the observed water vapour anomaly is likely to be connected to the volcanoes and could be explained by the regolith-atmosphere water vapour exchange. On the basis of a new theoretical approach to the process of diffusion of adsorbed water from the regolith to the atmosphere, a model of the observed anomaly was proposed. It implies an intensive vapour desorption during the day hours from the volcanic regolith, which was assumed to be different in composition from that of surrounding highlands.

Poster; International audience

— The COMET program is a program for the collection of micron to submicron interplanetary dust particles in low Earth orbits. Since collection takes place as the Earth crosses a given meteor stream, the particles are mainly of cometary origin. The grain remnants, located at their impact positions on high purity metallic collectors, are analysed in the laboratory for chemical and isotopical identification. The COMET-1 experiment took place in 1985 October, during encounter with the Draconid meteor stream, related to the Giacobini-Zinner comet. The fluence of extraterrestrial grains that had impacted our detectors was ∼10x higher than the value of the mean meteroid fluence at ∼1AU, which suggests that most of the grains originated from the Giacobini-Zinner comet. One of the most important results of their chemical analysis was that ∼90% of them are enriched in low Z elements (C and O have undoubedly been identified). They could contain a CHON phase similar to that observed in the close environment of Halley's nucleus. The first imagery of the grain remnants by field emission scanning electron microscopy suggests that they are very low density aggregates still present at the impacting positions which, in most cases, are very different from the impact craters observed for the same mean relative velocity for full grains of the same size. These results show that the COMET program has constituted an important step towards the analysis of cometary material and the understanding of the evolution of the early Solar System.

The study characterizes Syrtis Major, an old, low relief volcanic plateau near the equatorial regions of Mars, on the basis of ISM data in order to characterize the spectral properties of the surface, to identify the major mafic mineralogy of the volcanic materials, and to derive estimates of the chemistry of these minerals. The value and spatial distribution of four primary spectral variables (albedo, continuum slope, wavelength of the ferric-ferrous band minimum, and area of the ferric-ferrous absorption) are mapped and coregistered to Viking digital photomosaics. It is shown that although there is a high degree of overall spectral variability on the plateau, the key indicators of mafic mineralogy are relatively homogeneous.

International audience; The Rosetta spacecraft accomplished a flyby of Mars on its way to 67P/Churyumov-Gerasimenko on 25 February 2007. In this paper we describe the measurements obtained by the M channel of the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS-M) and the first scientific results derived from their analysis. The broad spectral coverage of the VIRTIS-M in the IR permitted the study of various phenomena occurring in the Martian atmosphere; observations were further exploited to achieve accurate absolute radiometric calibration. Nighttime data from the VIRTIS-M constrain the air temperature profile in the lower atmosphere (5-30 km), using variations in CO2 opacity at 4.3 mum. A comparison of this data with the global circulation model (GCM) by Forget et al. (1999) shows a trend of slightly higher air temperature in the VIRTIS-M retrievals; this is accompanied by the presence of moderate decreases (˜5 K) in large sections of the equatorial region. This is potentially related to the occurrence of water ice clouds. Daytime data from the VIRTIS-M reveal CO2 non-local thermodynamic equilibrium emission in the high atmosphere. A mapping of emission intensity confirms its strict dependence on solar zenith angle. Additionally, devoted limb observations allowed the retrieval of vertical emission intensity profiles, indicating a peak around 105 km in southern tropical regions. Ozone content can be effectively monitored by the emission of O2 (a1Deltag) at 1.27 mum. Retrieved emission intensity shows that polar regions are particularly rich in ozone. Aerosol scattering was observed in the 1-2.5 mum region above the night region above the night disk, suggesting the occurrence of very high noctilucent clouds.

International audience

The spectrum of some portion of the Phobos surface was measured at the same points by two instruments (KRFM and ISM) on board the Phobos-2 mission in two ranges: 0.315–0.6 and 0.8–3.1 μm. An example of a spectrum based on data from both experiments obtained in the same locations is presented and discussed. It is substantially different from a previously published “average” spectrum of Phobos / 1 /. There is no direct analog to the presented spectrum among the known reflectivity spectra of meteorites and asteroids. The spectral reflectivity of observed part of Phobos is like carbonaceous C1–C2 chondrites for the range λ μ m, but not at λ >0.8 μ m, where it shows a rise of reflectivity with wavelength even stronger than in the case of CM chondrites. No traces of the hydration band near 3 μm are visible. The nature of the surface layer is probably complicated, and it consist of inhomogeneous material.

Photometric limb to limb profiles of Mars were obtained in 8 narrow bands between 315 and 550 nm from the Phobos-2 spacecraft. Tentative results of analysis are presented in terms of optical properties of the atmosphere and surface. Imaginary part of the refraction index ae from 0.0075 to 0.02 for 315 nm and from 0.005 to 0.01 for 550 nm was estimated for the “constant” dust haze, using Mie theory for spherical particles. These values of ae are in a few times higher than obtained by laboratory tests of terrestrial analogues including basalt, andesit and montmorillonite. Two explanations are possible: influence of irregular shape of particles and/or presence of some more absorbing substances ( as goethit ). Particle sizes a few tenths micron having refraction index 1.55 are compatible with the discussed model of the “constant” haze. Full shape of the near equatorial photometric profile on 550 nm can be explained by the slightly absorbed atmosphere ( with the optical depth 0.4 and imaginary part of the refraction index 0.0075 ). Icy particles with the same average sizes as in the haze (r m =0.4 microns) but with more narrow size distribution can explaine the bright spot above the Arsia Mons. Optical depth τ =0.1 and column mass density 7·10 −5 g cm −2 of the icy clouds were evaluated.

Definitive exposures of pristine, ancient crust on Mars are rare, and the finding that much of the ancient Noachian terrain on Mars exhibits evidence of phyllosilicate alteration adds further complexity. We have analyzed high-resolution data from the Mars Reconnaissance Orbiter in the well-exposed Noachian crust surrounding the Isidis basin. We focus on data from the Compact Reconnaissance Imaging Spectrometer for Mars as well as imaging data sets from High Resolution Imagine Science Experiment and Context Imager. These data show the lowermost unit of Noachian crust in this region is a complex, brecciated unit of diverse compositions. Breccia blocks consisting of unaltered mafic rocks together with rocks showing signatures of Fe/Mg-phyllosilicates are commonly observed. In regions of good exposure, layered or banded phyllosilicate-bearing breccia rocks are observed suggestive of pre-Isidis sedimentary deposits. In places, the phyllosilicate-bearing material appears as a matrix surrounding mafic blocks, and the mafic rocks show evidence of complex folded relationships possibly formed in the turbulent flow during emplacement of basin-scale ejecta. These materials likely include both pre-Isidis basement rocks as well as the brecciated products of the Isidis basin–forming event at 3.9 Ga. A banded olivine unit capped by a mafic unit covers a large topographic and geographic range from northwest of Nili Fossae to the southern edge of the Isidis basin. This olivine-mafic cap combination superimposes the phyllosilicate-bearing basement rocks and distinctly conforms to the underlying basement topography. This may be due to draping of the topography by a fluid or tectonic deformation of a previously flatter lying morphology. We interpret the draping, superposed olivine-mafic cap combination to be impact melt from the Isidis basin–forming event. While some distinct post-Isidis alteration is evident (carbonate, kaolinite, and serpentine), the persistence of olivine from the time of Isidis basin suggests that large-scale aqueous alteration processes had ceased by the time this unit was emplaced.

International audience

We present an Iterative Linear Spectral Unmixing Model (ILSUM) which is aimed at finding the main surface components that contribute to the signal in visible and infrared hyperspectral images. We processed the global dataset of the OMEGA imaging spectrometer onboard Mars Express up to orbit 5300, covering two martian years. We also present a preliminary test on AVIRIS data on the Cuprite (Nevada) site. We use ILSUM to identify the contribution of each endmember of an input library containing laboratory spectra of ices and mineral powders that are representative of the main mineral families. Synthetic spectra (pure slope endmembers) are included to account at first order for aerosol and grain size variations. Applied to the global OMEGA data set, this algorithm provides a distribution map for the main minerals present on the martian surface, which appears to be mainly dominated by pyroxenes, olivine, ferric oxides, with localized exposures of sulfates and phyllosilicates.

International audience