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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. [ABSTRACT FROM AUTHOR]

MicrOmega is a near-IR hyperspectral microscope designed to characterize in situ the texture and composition of the surface materials of the Hayabusa2 target asteroid. MicrOmega is implemented within the MASCOT lander (Ho et al. in Space Sci. Rev., 2016, this issue, doi:10.1007/s11214-016-0251-6). The spectral range (0.99-3.65 μm) and the spectral sampling ( $20~\mbox{cm}^{-1}$ ) of MicrOmega have been chosen to allow the identification of most potential constituent minerals, ices and organics, within each 25 μm pixel of the $3.2\times 3.2~\mbox{mm}^{2}$ FOV. Such an unprecedented characterization will (1) enable the identification of most major and minor phases, including the potential organic phases, and ascribe their mineralogical context, as a critical set of clues to decipher the origin and evolution of this primitive body, and (2) provide the ground truth for the orbital measurements as well as a reference for the analyses later performed on returned samples. [ABSTRACT FROM AUTHOR]

In situ images of the 67P/Churyumov-Gerasimenko nucleus acquired by the CIVA cameras on-board PHILAE revealed a rough landscape dominated by consolidated materials. These data provide a unique view to constrain the past and present conditions prevailing at the surface of the comet. A quantitative analysis of microscopic structures (fractures and pebbles) is derived using a manual extraction from the images. Fractures/cracks are rather ubiquitous at various spatial scales with network and size (from sub-cm to 10 cm) well correlated to the texture of the landscape. The pebble size distributions are derived and compared to the size distribution of other cometary materials. The nature of the landscape is then discussed in relation to endogenic and exogenic processes of surface modification. The block seen in CIVA no. 1 is interpreted to be close-ups of fractured boulder/cliff belonging to the boulder field identified from the orbit near Abydos, this boulder field being itself the result of gravitational regressive erosion due to sublimation. The observed fractures are best explained by thermal insolation leading to thermal fatigue and/or to loss of volatile materials. This surficial fragmentation (up to >10 cm length) could generate macroscopic erosion that is also visible at larger scale from the orbit. There is at least an intriguing possibility that the pebbles are remnants of primordial accretion processes. We thus speculate that the Abydos landscape could be in favour of pebble accretion model instead of runaway coagulation model with a formation location in the outer region of the Solar system. [ABSTRACT FROM AUTHOR]

Context. On 12 November 2014, the European mission Rosetta delivered the Philae lander on the nucleus of comet 67P/Churyumov- Gerasimenko (67P). After the first touchdown, the lander bounced three times before finally landing at a site named Abydos. Aims. We provide a morphologically detailed analysis of the Abydos landing site to support Philae's measurements and to give context for the interpretation of the images coming from the Comet Infrared and Visible Analyser (CIVA) camera system onboard the lander. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 6 December 2014 to perform the analysis of the Abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. We also computed the albedo and spectral reddening maps. Results. The morphological analysis of the region could suggest that Philae is located on a primordial terrain. The Abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km2 talus deposit rich in boulders. The boulder size frequency distribution gives a cumulative power-law index of -4:0 + 0:3=-0:4, which is correlated with gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. The average value of the albedo is 5.8% at λ1 = 480:7 nm and 7.4% at λ2 = 649:2 nm, which is similar to the global albedos derived by OSIRIS and CIVA, respectively. [ABSTRACT FROM AUTHOR]

Introduction: The Ryugu samples brought back by the Hayabusa2 spacecraft in December 2020 have been delivered to the JAXA Extraterrestrial Curation Center [1]. Bulk samples and then individual grains have been picked up and stored into sapphire dishes, weighted, and analyzed with an optical microscope, FTIR spectroscopy, and MicrOmega hyperspectral imaging [2-4] for initial description. The MicrOmega instrument used in the JAXA Extraterrestrial Curation Center is a near-infrared (NIR) hyperspectral microscope [5]. It has a total field of view of ~5 mm x 5 mm, with a resolution of ~22 µm/pixel in the focal plane. It covers the spectral domain from 0.99 µm to ~3.6 µm, enabling the identification of most candidate minerals and molecules of relevance (e.g. mafic minerals, altered phases, salts, ices, aliphatic/aromatic CH, NH-rich compounds) [6]. In particular, in the spectral domain of MicrOmega, carbonates have a strong characteristic double absorption band in the 3.3-3.5 µm range, accompanied by two other weaker bands around 2.5 and 2.3 µm. The exact position of these bands varies with the cation content of the carbonate [7]. Iron-bearing carbonates also show a strong Fe2+ absorption below 1.5 µm. Initial analyses with MicrOmega were first made on the bulk samples from chambers A and C of the Hayabusa 2 returned capsule, and then on individual grains stored in their sapphire dishes (by the end of 2021, ~180 individual grains have been analyzed), as well as 14 sub-bulks. Such extensive characterization provides a unique opportunity to assess the different processes that shaped Ryugu's material. Here, we focus on the MicrOmega analyses of Ryugu carbonate-rich grains and inclusions which record the alteration processes encountered on Ryugu parent body. Results: Spectra of the Ryugu samples at the mm-scale share common features: a very low reflectance (2-3%), an absorption band centered around 2.715 µm attributed to OH, and a weak absorption centered around 3.4 µm attributed to a variety of CH-rich compounds and carbonates [2]. Only at a sub-millimeter scale do heterogeneities clearly show up, either or both at grain level or as inclusions within grains. In total, more than 200 carbonate-rich areas larger than ~45 µm (2x2 MicrOmega pixels) have been detected among the grains and bulks/sub-bulks observed with MicrOmega by the end of 2021 (which does not preclude the presence of carbonates at finer scale). While most of the detections are smaller than ~100 µm in size, the largest carbonate-rich areas can reach several hundreds of µm, displaying various kinds of morphologies. The analysis of the position of the absorption features enabled the identification of various types of carbonates, similar to dolomite and breunnerite for the large majority of them. These various detections and the context in which they are made will be presented. Implications for the alteration processes encountered on Ryugu's parent body will also be discussed. [ABSTRACT FROM AUTHOR]

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 Ryugu [1,2]. Its surface was first sampled on February 22, 2019 ("bulk A"), then on July 11, 2019, close to a 15-meter large artificial crater, so as to possibly access sub-surface material ("bulk C") [3]. The collected samples are now kept at ISAS (Institute of Space and Astronautical Science) for a first round of preliminary analyses, with the objective of characterizing in a non-destructive manner both the bulk samples and a few hundreds of grains extracted from them [4]. In particular, the goal is 1) to support their further detailed characterization by the international Initial Analysis Teams, and 2) to build a catalogue of the grains, accessible to the international community through AO selection, starting mid-2022. Importantly, the analyzed samples have always been kept, since their collection, in a fully clean and controlled environment either under vacuum or ultra-clean GN2. Methods: The preliminary characterization of these samples is being conducted with a visible microscope with six color filters [4], a FTIR spectrometer (1-4 μm) [4], and MicrOmega, a hyperspectral microscope [5], operating in the near-infrared range (0.99-3.65 μm) where diagnostic signatures of most candidate minerals and molecules of relevance (e.g. mafic minerals, altered phases, salts, ices, aliphatic/aromatic CH, NH-rich compounds) can be found. For each 22.5x22.5 μm² pixel of the 250x256 pixels² field of view, the reflectance spectrum is retrieved in up to 400 contiguous spectral channels. Both the negligible amount of illuminating power at less than 10-8 W/px and the lack of contact with the samples allow entirely non-destructive and non-invasive characterization. By the beginning of 2022, bulk samples from chamber A and chamber C of the Hayabusa2 returned capsule (each divided into 3 sub-bulks), as well as >200 individual grains and 14 "small-bulks" extracted from them have been analyzed with MicrOmega. Results: When analyzed at the mm-scale by averaging thousands of pixels, the spectra of bulk A and bulk C exhibit a pattern similar to those acquired remotely down to the meter scale by the NIRS3 IR spectrometer on board Hayabusa2 [6]. The global reflectance is extremely low, 2-3 %, in agreement with the measurements of the ONCs and NIRS3 at Ryugu [7,8], and consistent with the taxonomic spectral classification of Ryugu as a C-type asteroid [1,2]. The main spectral feature is the diagnostic OH absorption centered at 2.715 +/-0.005 μm, position compatible with that of NIRS3 spectra [8,9]. No significant differences can be observed between bulk A and bulk C for this specific feature. MicrOmega spectra also exhibit a broad feature in the 3.3-3.5 μm range, centered around 3.4 μm, present throughout the sub-bulk samples. This feature is considered indicative of the large-scale presence of a variety of CHrich compounds and carbonates. A fainter ~3.1 μm broad feature, indicative of the presence of NH-bearing compounds is also detected, although with varying and much fainter intensities. Only at a sub-millimeter scale do heterogeneities clearly show up, either or both at grain level or as inclusions within grains. Detections include for example: 1) carbonates of various compositions, detected on a rather large number of occurrences with sizes ranging from a few tens to a few hundreds of micrometers [10]; 2) spots enriched in organics, in particular through a 3.4 μm feature indicative of the presence of aliphatic compounds; 3) spots enriched in a nitrogen-rich phase, through a ~3.1 μm feature sometimes coupled to additional spectral features. These detections, as well as others, will be presented and candidates will be discussed. Noticeably, no chondrules nor refractory inclusions have been identified yet. Conclusion: The initial spectral characterization of the returned samples by MicrOmega currently points towards Ryugu containing a fascinating variety of grains, including OH-, CH- and NH- rich compounds spread at a global scale, and alteration products, among which highly diagnostic carbonates. The occurrence of volatile-rich species, likely originating from the outer solar system, would support Ryugu having preserved some of its building blocks, together with their partially altered phases. The Hayabusa2 returned samples, thus, appear among the most primordial material available in our laboratories. [ABSTRACT FROM AUTHOR]

Microscopy and spectroscopy are important methods of studies. The use of a microscope onboard a spacecraft is connected with the fact that the closer approach to the objects and the switch to the in situ measurement methods have become possible. The combination of taking an image and performing a spectral analysis forms a new type of instrument, so-called videospectrometers. The scientific payload of the Phobos-Grunt spacecraft includes the microscope spectrometer designed to analyze the composition of the surface regolith of Phobos in detail. [ABSTRACT FROM AUTHOR]

Channel C of the orbital hyperspectrometer OMEGA onboard Mars Express spacecraft has delivered data on the distribution and seasonal variability of water ice spectral features at 1.25, 1.5, 2.0 μm, based on which one may conclude about the thickness of ice coverage and microstructure of the upper, optically active ice layer on the Martian surface. Data covering polar regions during spring-to-summer periods of both hemispheres have been analyzed. Microstructure of the North polar cap, as well as the residual frost deposits of the seasonal South polar cap, have revealed remarkable zonal variations with regularly located maxima. Based on the comparison with the atmospheric general circulation model results, it has been proposed that these variations result from the impact of mesoscale inertial waves in the circumpolar vortex on water exchange processes between the atmosphere and planetary surface. [ABSTRACT FROM AUTHOR]

Parameterization of the spectral dependence of the optical characteristics of Martian aerosols has been proposed for processing the results of measurements of outgoing radiation. A method for retrieving the altitude profiles of the microphysical characteristics of Martian aerosols from the limb spectrometry of the OMEGA instrument of the Mars Express mission have been developed. For one of the observational sessions, the altitude profiles of the concentration and the modal radius of the size distribution function of aerosol particles retrieved with the proposed parameterization are presented. For the purpose of the interpretation of the data acquired from the optical remote sensing of planetary atmospheres, we consider how the spectral dependence of aerosol optical characteristics, in particular the volume coefficients of aerosol scattering and absorption and the phase function, can be parameterized in a specified, probably wide, spectral range. The method of such a parameterization has been proposed for the cases of a fixed chemical composition of the aerosol materials dominating in the atmosphere. It has been shown that these cases allow the required spectral dependences to be presented as a function of a small number of parameters, for which the parameters of the size distribution function of aerosol particles can be successfully used. However, since such direct calculations of the aerosol characteristics require an inadmissibly long period of time for the tasks of interpretation of the remote sensing data, an algorithm for organizing the parameterization function as a special, preliminary generated computer database has been suggested. This database provides the continuity in the dependence on the parameters, the specified computation accuracy, and the required output speed of the results. As a specific application, the parameterization of the spectral dependence of the optical characteristics of the Martian aerosols has been proposed for the tasks of processing the results of measurements of outgoing radiation. As a result, the method for retrieving the altitude profiles of the microphysical characteristics of Martian aerosols from the limb spectrometric measurements of the OMEGA instrument of the Mars Express mission has been developed. For one of the observational sessions, the altitude profiles of the concentration and the modal radius of the size distribution function of aerosol particles retrieved with the proposed parameterization are presented. [ABSTRACT FROM AUTHOR]

The results of the analysis of the spectral observations of Mars carried out with the OMEGA spectrometer onboard the Mars Express spacecraft are presented. The data from one of the spectrometer’s channels working in the near-IR spectral range (0.93–2.69 µm) were analyzed. This range includes the characteristic absorption bands of both condensed water phases (ice and frost) and bound water contained in hydrated minerals of the Martial soil. From the 1.93-µm band indicating the presence of these minerals, global maps of the bound-water index have been made. They show a noticeable latitude dependence of the index: the largest values refer to high latitudes (>60°), while they gradually diminish toward the equator. Seasonal variations of the spectral index obtained by the 1.93-µm band are connected with the hydration-dehydration processes occurring in hydrogenous minerals when the temperature of the soil and the relative humidity in the near-surface atmospheric layer are changing. The evolution of the spectral absorption bands of water ice (1.2 and 1.5 µm) dependent on the season testifies to the changes in the microstructure of the surface layer in the North ploar cap caused by the sublimate re-crystallization processes in the ice sheet. The spatial pattern of the location of the areas where the microstructure most quickly grows could be formed under the influence of the stationary atmospheric waves. [ABSTRACT FROM AUTHOR]

Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L’Eau, les Glaces et l’Activitié) instrument1,2, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars³), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars’s history4. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)5 of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability. [ABSTRACT FROM AUTHOR]

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright ‘dipole’ feature surrounded by a cold ‘collar’ at its north pole. The polar dipole is a ‘double-eye’ feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus’ south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. [ABSTRACT FROM AUTHOR]

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90–120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft and ground-based observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission owing to a lack of data and of an adequate observing geometry. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 µm, extending from 90 to 120 km altitude, and of night-side O2 emission extending from 95 to 100 km. The CO2 emission peak occurs at ∼115 km and varies with solar zenith angle over a range of ∼10 km. This confirms previous modelling, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96 km ± 1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted. [ABSTRACT FROM AUTHOR]