Temperature-dependent VNIR spectroscopy of sodium sulfates

The surfaces of the icy Galilean satellites Europa, Ganymede and Callisto, dominated by water ice, also show substantial amounts of non-water-ice compounds both at regional and local scales. These satellites will be the subject of close exploration by the ESA JUICE mission and the NASA Europa Clipper mission, which will focus on Ganymede and Europa, respectively. Among non-water-ice compounds thought to exist on the surfaces of the Jovian icy satellites, hydrated salt minerals have been proposed to exist as a by-product of endogenic processes. In particular, Europa and Ganymede's non-ice material appears to be a complex mixture of sulfate hydrates and other materials. Seasonal cycles of hydration-dehydration at Martian Polar Caps boundaries have also been suggested for Na-sulfate compounds mirabilite and thénardite. Safe detection of these minerals shall rely on laboratory spectroscopic analysis of these materials carried out under appropriate environmental conditions. Following the selection of a Europlanet Transnational Access (TA) 2020 Research Infrastructure proposal, we took advantage of the Cold Surfaces Spectroscopy (CSS) facility at the Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) to acquire visible to near-infrared spectral profiles of anhydrous sodium sulfate or thénardite (Na2ṡSO4) and sodium sulfate decahydrate or mirabilite (Na2SO4ṡ10H2O). The samples were measured under cryogenic conditions representative of real planetary surfaces. The sulfates were first sieved in three different grain size ranges: <50 μm, 75-100 μm, and 125-150 μm. Each grain size was measured with the SHINE Spectro-Gonio-Radiometer facility in the overall 0.5-5.0 μm spectral range, with spectral resolution decreasing with increasing wavelength. For each sample, the overall 80-275 K temperature range was acquired in 12 steps. In the case of anhydrous sodium sulfate (thénardite), our spectral profiles reveal absorption features at 1.9 and ∼3 μm, due to a weak but unavoidable hydration of the sample, although this has always been optimally preserved prior to the measurements. On the other hand, the main absorption of sodium sulfate in the considered spectral range is centered at about 4.5 μm, and shows a clear dependence on the grain size, whereas the dependence on temperature is weaker. The spectral profiles of sodium sulfate decahydrate (mirabilite) are significantly different. Given the high level of hydration of this mineral, in the 1-3 μm range we mainly observe the spectral signatures due to combinations and overtones of the fundamental vibration modes of the water molecule, together with SO42-H2O complexes vibrations; the shape and intensity of these bands show a marked dependence both on the grain size and on the temperature, with low temperatures revealing a fine structure. We analyze the spectral behaviour of the diagnostic signatures of these minerals as a function of both grain size and temperature, deriving trends related to specific spectral indices such as band center, band depth, band area, and bandwidth. We plan to develop this work in the near future by measuring VIS-NIR spectra of magnesium chlorides following the same approach

Temperature-dependent VNIR spectroscopy of thénardite and mirabilite

In the framework of the EuroPlanet 2020 Research Infrastructure (RI) programme, we took advantage of the CSS distributed planetary simulation facility at IPAG-Grenoble to perform a series of laboratory measurements aimed to acquire VIS-NIR spectra of anhydrous sodium sulfate (thénardite) and sodium sulfate decahydrate (mirabilite), in three different grain sizes and in a broad range of cryogenic temperatures, representative of real planetary surfaces. These measurements are key to correctly interpret data acquired by spectrometers carried onboard ongoing and future interplanetary space missions aimed at various planetary bodies, particularly the Jovian icy satellites (JUICE, Europa Clipper) and Mars (ExoMars 2020, Mars 2020)

Identification of Ammonium Salts on Comet 67P/C-G Surface from Infrared VIRTIS/Rosetta Data Based on Laboratory Experiments. Implications and Perspectives

The nucleus of comet 67P/Churyumov-Gerasimenko exhibits a broad spectral reflectance feature around 3.2 $\mu$m, which is omnipresent in all spectra of the surface, and whose attribution has remained elusive since its discovery. Based on laboratory experiments, we have shown that most of this absorption feature is due to ammonium (NH4+) salts mixed with the dark surface material. The depth of the band is compatible with semi-volatile ammonium salts being a major reservoir of nitrogen in the comet, which could dominate over refractory organic matter and volatile species. These salts may thus represent the long-sought reservoir of nitrogen in comets, possibly bringing their nitrogen-to-carbon ratio in agreement with the solar value. Moreover, the reflectance spectra of several asteroids are compatible with the presence of NH4+ salts at their surfaces. The presence of such salts, and other NH4+-bearing compounds on asteroids, comets, and possibly in proto-stellar environments, suggests that NH4+ may be a tracer of the incorporation and transformation of nitrogen in ices, minerals and organics, at different phases of the formation of the Solar System

Spectrophotometry of extra-terrestrial matter

La spectroscopie en réflectance est l’une des techniques majeures permettant d’obtenir des informations physiques et minéralogiques sur la surfaces des corps planétaires. Cependant, la réflectance d’un corps dépend fortement de paramètres extérieurs à sa surface, tels que sa température ou encore la configuration de l’éclairement et de l’observation. Le nouveau spectro-gonio radiomètre de l’IPAG, SHADOWS, a été spécialement conçu pour réaliser des mesures de réflectance bidirectionnelle de surfaces sombres et de petite taille, telles que les météorites. Ce goniomètre compte également deux cellules environnementales, MIRAGE et IceBERG, permettant de placer les échantillons étudiés dans des conditions de température et pression similaires aux petis corps du Système Solaire. L’analyse des signatures d’hydratation détectées sur des spectres de météorites en conditions astéroïdales a permis de mettre en évidence l’altération de la minéralogie due à la haute température. Un nouveau modèle de déconvolution a été utilisé pour séparer et analyse de manière indépendante les composantes de la bande à 3-µm. La comparaison entre les mesures effectuéesen laboratoire et les observations d’astéroïdes ont mis en évidence un lien entre cette signature spectrale et l’histoire d’altération aqueuse et thermique de la surface. La dépendance de la réflectance avec la géométrie de la mesure a été montré par une série d’analyse en réflectance bidirectionnelle de différentes surfaces. Ces résultats ont ensuite été appliqués sur des simulations d’astéroïde, pour montrer l’effet de la forme du corps sur son spectre intégré.Reflectance spectroscopy is one of the major techniques used to retrieve information on physical and mineralogical configuration of the surface of planetary bodies. However, the reflectance of a surface strongly depends on parameters unrelated to its surface, such as the temperature or the illumination and observation configuration. The new spectro-gonio radiometer at IPAG, SHADOWS, has been specially designed to conduct bidirectional reflectance spectroscopy on dark and small surfaces, such as meteorites. This goniometeralso owns two environmental cells, MIRAGE and IceBERG, allowing the study on thesamples under similar temperature and pressure conditions as the Solar System small bodies. The analysis of the hydration signatures on meteoritic spectra under asteroidal condition showed the alteration of the mineralogy by the high temperature. A new deconvolution model has been used to separate and independently analyze the components of the 3-µm band. Comparison between laboratory measurements and telescopic observations of asteroids highlighted the link between this spectral signature and the aqueous and thermal alteration history of the surface. A serie of bidirectional reflectance spectroscopyon various surfaces showed that the reflectace strongly depends on the geometrical configuration of the measurement. These results have been then applied to a simulated asteroid to show the effect of the shape of the body on its integrated spectrum

Spectrophotométrie de la matière extra-terrestre

Reflectance spectroscopy is one of the major techniques used to retrieve information on physical and mineralogical configuration of the surface of planetary bodies. However, the reflectance of a surface strongly depends on parameters unrelated to its surface, such as the temperature or the illumination and observation configuration. The new spectro-gonio radiometer at IPAG, SHADOWS, has been specially designed to conduct bidirectional reflectance spectroscopy on dark and small surfaces, such as meteorites. This goniometeralso owns two environmental cells, MIRAGE and IceBERG, allowing the study on thesamples under similar temperature and pressure conditions as the Solar System small bodies. The analysis of the hydration signatures on meteoritic spectra under asteroidal condition showed the alteration of the mineralogy by the high temperature. A new deconvolution model has been used to separate and independently analyze the components of the 3-µm band. Comparison between laboratory measurements and telescopic observations of asteroids highlighted the link between this spectral signature and the aqueous and thermal alteration history of the surface. A serie of bidirectional reflectance spectroscopyon various surfaces showed that the reflectace strongly depends on the geometrical configuration of the measurement. These results have been then applied to a simulated asteroid to show the effect of the shape of the body on its integrated spectrum.La spectroscopie en réflectance est l’une des techniques majeures permettant d’obtenir des informations physiques et minéralogiques sur la surfaces des corps planétaires. Cependant, la réflectance d’un corps dépend fortement de paramètres extérieurs à sa surface, tels que sa température ou encore la configuration de l’éclairement et de l’observation. Le nouveau spectro-gonio radiomètre de l’IPAG, SHADOWS, a été spécialement conçu pour réaliser des mesures de réflectance bidirectionnelle de surfaces sombres et de petite taille, telles que les météorites. Ce goniomètre compte également deux cellules environnementales, MIRAGE et IceBERG, permettant de placer les échantillons étudiés dans des conditions de température et pression similaires aux petis corps du Système Solaire. L’analyse des signatures d’hydratation détectées sur des spectres de météorites en conditions astéroïdales a permis de mettre en évidence l’altération de la minéralogie due à la haute température. Un nouveau modèle de déconvolution a été utilisé pour séparer et analyse de manière indépendante les composantes de la bande à 3-µm. La comparaison entre les mesures effectuéesen laboratoire et les observations d’astéroïdes ont mis en évidence un lien entre cette signature spectrale et l’histoire d’altération aqueuse et thermique de la surface. La dépendance de la réflectance avec la géométrie de la mesure a été montré par une série d’analyse en réflectance bidirectionnelle de différentes surfaces. Ces résultats ont ensuite été appliqués sur des simulations d’astéroïde, pour montrer l’effet de la forme du corps sur son spectre intégré

The impact of asteroid shapes and topographies on their reflectance spectroscopy

International audienceHere we report the comparison between unresolved reflectance spectroscopy of Solar System small bodies and laboratory measurements on reference surfaces. We measure the bidirectional reflectance spectroscopy of a powder of howardite and a sublimation residue composed of a Ceres analogue. The spectra are then inverted using the Hapke semi-empirical physical model and the MRTLS parametric model to be able to simulate the reflectance of the surfaces under any geometrical configuration needed. We note that both models enable an accurate rendering of the reflectance spectroscopy, but the MRTLS model adds less noise on the spectra compared to the Hapke model. Using the parameters resulting from the inversions, we simulate two spherical bodies and the small bodies (1)Ceres and (4)Vesta whose surfaces are homogeneously covered with the Ceres analogue and powder of howardite respectively. We then simulate various scenarios of illumination and spectroscopic observations, i.e. spot-pointing and fly-bys, of these small bodies for phases angles between 6° and 135°. The unresolved reflectance spectroscopy of the simulated bodies is retrieved from the resulting images, and compared to the reflectance spectroscopy of the reference surface measured in the laboratory. Our results show that the photometric phase curves of the simulated bodies are different from the reference surfaces because of the variations of the local incidence and emergence angles due to the shape and topography of the surface. At low phase angle, the simulated bodies are brighter than the reference surfaces, with lower spectral slope and shallower absorption bands. We observe the maximum differences at wide phase angles with the various simulated observations of (4)Vesta due to its high surface topography. Finally, we highlight the differences in the spectral parameters derived from the unresolved observations at 30° with laboratory measurements acquired under a single geometrical configuration

Comparison of photometric phase curves resulting from various observation scenes

International audienceThe Solar System small bodies can be observed from ground-based or Earth orbiting telescopes but only span over a few pixels on the images due to their distance to the observer, their small size and atmospheric conditions blurring the images. The highest spatial resolution on the surface is achieved by in-situ observations by spacecrafts orbitting their target

Comparison of photometric phase curves resulting from various observation scenes

International audienceThe Solar System small bodies can be observed from ground-based or Earth orbiting telescopes but only span over a few pixels on the images due to their distance to the observer, their small size and atmospheric conditions blurring the images. The highest spatial resolution on the surface is achieved by in-situ observations by spacecrafts orbitting their target

Comparison of photometric phase curves resulting from various observation scenes

International audienceThe Solar System small bodies can be observed from ground-based or Earth orbiting telescopes but only span over a few pixels on the images due to their distance to the observer, their small size and atmospheric conditions blurring the images. The highest spatial resolution on the surface is achieved by in-situ observations by spacecrafts orbitting their target

Detection and identification of rabbit liver metallothionein-2 subisoforms by capillary zone electrophoresis - inductively coupled plasma spectrometry and microbore HPLC - electrospray mass spectrometry

International audienceTwo recently developed approaches to the subisoform-specific detection and identification methallothionein (MT) isoforms are compared. They are based on the coupling of capillary electrophoresis with ICP MS and microbore chromatography with electrospray MS. The resolution of HLPC is judged to be slightly better since differently metaliated forms of the same sub-isoform can be separated. Detection by electrospray MS is mandatory to avoid the attribution of artefact signals observed in element-specific chromatograms to different sub-isoforms.Two recently developed approaches to the subisoform-specific detection and identification of metallothionein (MT) isoforms are compared. They are based on the coupling of capillary electrophoresis with ICP MS and microbore chromatography with electrospray MS. The resolution of HPLC is judged to be slightly better since differently metallated forms of the same sub-isoform can be separated. Detection by electrospray MS is mandatory to avoid the attribution of artefact signals observed in element-specific chromatograms to different sub-isoforms