The Composition of Comets

This paper is the result of the International Cometary Workshop, held in Toulouse, France in April 2014, where the participants came together to assess our knowledge of comets prior to the ESA Rosetta Mission. In this paper, we look at the composition of the gas and dust from the comae of comets. With the gas, we cover the various taxonomic studies that have broken comets into groups and compare what is seen at all wavelengths. We also discuss what has been learned from mass spectrometers during flybys. A few caveats for our interpretation are discussed. With dust, much of our information comes from flybys. They include {\it in situ} analyses as well as samples returned to Earth for laboratory measurements. Remote sensing IR observations and polarimetry are also discussed. For both gas and dust, we discuss what instruments the Rosetta spacecraft and Philae lander will bring to bear to improve our understanding of comet 67P/Churyumov-Gerasimenko as "ground-truth" for our previous comprehensive studies. Finally, we summarize some of the initial Rosetta Mission findings.Comment: To appear in Space Science Review

Observations of Rocks in Jezero Landing Site: SuperCam/LIBS technique overview of results from the first six months of operations.

On-board the Perseverance rover, the SuperCam instrument is being used as a remote-sensing facility to analyze rocks and soils targets. SuperCam is a suite of five coaligned techniques: just like ChemCam (onboard MSL/Curiosity rover on Mars since 2012), it uses the Laser Induced Breakdown Spectroscopy (LIBS) technique to determine the elementary composition of the targets, but it also uses Raman (for the first time in planetary science) and visible-infrared (VISIR - for the first time in situ) spectroscopic methods in order to access some mineralogical and structural information. A microphone gives access to some physical parameters of the sampled rocks (such as hardness) as well as to some atmospheric parameters (wind direction). These chemical and mineralogical analyses are contextualized thanks to a color remote micro-imager (RMI). In this study, we focus mainly on the LIBS results obtained so far

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds

Diffusion de la lumière par des agrégats irréguliers : simulations numériques et expérimentales, applications aux petits corps dans le système solaire.

The light scattered by particles present in cometary comæ can be used to provide an estimate of the size distribution, structure and composition of the particles.Experimental simulations I participated in the definition and calibration of the ICAPS-PE (LSU) experiment selected by ESA for the ISS. It will produce fractal aggregates and analyze the light they scatter at several wavelengths and phase angles. I validated the concept of the instrument and developed a new concept to measure the Stokes parameters with liquid crystal variable retarders. I analyzed the light scattering measurements performed with the PROGRA2 experiment for coated spherical particles. The results give an estimate of the width and complex optical indices of absorbing mantles.Numerical simulationsI developed a model of cometary coma to analyze polarimetric observations in terms of physical properties of solid particles. The model consists of aggregates (up to 256 spheroidal grains) and oblate spheroidal particles. A size distribution with a power law of coefficient -3 between radii values of 0.1 and 20 microns and with around 50% in mass of organics and silicates can reproduce the phase angle and wavelength variations of the polarization of C/1995 O1 (Hale-Bopp). The same model was used to analyze the interplanetary dust cloud. A size distribution between radii of 0.1 and 100 microns can reproduce the linear polarization phase curve. The decrease of the linear polarization at 90 degrees with decreasing heliocentric distance canbe explained by the degradation of organics material from 50% to 0% in mass between 1.5 and 0.5 AU.Les particules cométaires sont des témoins de l'évolution du système solaire, dont les caractéristiques peuvent être estimées à partir de la lumière qu'elles diffusent et émettent.Je montre qu'un modèle de diffusion lumineuse par un nuage d'agrégats fractals et de sphéroïdes permet d'interpréter, en fonction de la distribution en taille et des matériaux constitutifs, des observations polarimétriques en angle de phase et longueur d'onde. Le modèle est en particulier appliqué à la comète Hale-Bopp, et au milieu interplanétaire en modélisant aussi les observations thermiques.Je développe des outils de diffusion lumineuse (numériques et expérimentaux) pour analyser des agrégats analogues aux particules protoplanétaires qui seront formés avec ICAPS à bord de l'ISS. De façon complémentaire, une simulation expérimentale en vol parabolique avec PROGRA2 me permet de déterminer les propriétés physiques de microparticules d'intérêt astrophysique par des mesures polarimétriques

An Exploration of Heterogeneity in Supernova Type Ia Samples

International audienceWe examine three SNe Type Ia datasets: Union2.1, JLA and Panstarrs to check their consistency using cosmology blind statistical analyses as well as cosmological parameter fitting. We find that the Panstarrs dataset is the most stable of the three to changes in the data, although it does not, at the moment, go to high enough redshifts to tightly constrain the equation of state of dark energy, w. The Union2.1, drawn from several different sources, appears to be somewhat susceptible to changes within the dataset. The JLA reconstructs well for a smaller number of cosmological parameters. At higher degrees of freedom, the dependence of its errors on redshift can lead to varying results between subsets. Panstarrs is inconsistent with the other two datasets at about 2σ confidence level, and JLA and Union2.1 are about 1σ away from each other. For the Ω(0)m−w cosmological reconstruction, with no additional data, the 1σ range of values in w for selected subsets of each dataset is two times larger for JLA and Union2.1 as compared to Panstarrs. The range in Ω(0)m for the same subsets remains approximately similar for all three datasets. We find that although there are differences in the fitting and correction techniques used in the different samples, the most important criterion is the selection of the SNe, a slightly different SNe selection can lead to noticeably different results both in the purely statistical analysis and in cosmological reconstruction. We note that a single, high quality low redshift sample could help decrease the uncertainties in the result. We also note that lack of homogeneity in the magnitude errors may bias the results and should either be modeled, or its effect neutralized by using other, complementary datasets. A supernova sample with high quality data at both high and low redshifts, constructed from a few surveys to avoid heterogeneity in the sample, and with homogeneous errors, would result in a more robust cosmological reconstruction

Early Mars serpentinization-derived CH4 reservoirs, H2 induced warming and paleopressure evolution

International audienc

Methane storage capacity of the early martian cryosphere

Methane is a key molecule to understand the habitability of Mars due to its possible biological origin and short atmospheric lifetime. Recent methane detections on Mars present a large variability that is probably due to relatively localized sources and sink processes yet unknown. In this study, we determine how much methane could have been abiotically produced by early Mars serpentinization processes that could also explain the observed martian remanent magnetic field. Under the assumption of a cold early Mars environment, a cryosphere could trap such methane as clathrates in stable form at depth. The extent and spatial distribution of these methane reservoirs have been calculated with respect to the magnetization distribution and other factors. We calculate that the maximum storage capacity of such a clathrate cryosphere is about 2.1 × 10^19 – 2.2 × 10^20 moles of CH4, which can explain sporadic releases of methane that have been observed on the surface of the planet during the past decade (∼1.2 × 10^9 moles). This amount of trapped methane is sufficient for similar sized releases to have happened yearly during the history of the planet. While the stability of such reservoirs depends on many factors that are poorly constrained, it is possible that they have remained trapped at depth until the present day. Due to the possible implications of methane detection for life and its influence on the atmospheric and climate processes on the planet, confirming the sporadic release of methane on Mars and the global distribution of its sources is one of the major goals of the current and next space missions to Mars

Regolith weathering through heating samples under reducing conditions for Phobos surface studies

International audienceAtmosphereless bodies of the Solar System present surface evolution under the harsh conditions of space weathering. Their regolith are exposed to thermal cycling, cosmic and solar rays irradiation, solar wind sputtering and micrometeorites bombardment and vaporization. With time these materials accumulate optically active opaque particles such as nanophase metallic iron particles on the surface or rims of dust grainsor larger iron particles. The density increase in iron particles modifies the spectral properties of the material with a lowering of the particlesalbedo, and of the absorption bands amplitude generally associated with a global reddening of the spectral slope [1, 2].Previous studies have shown that nanophase iron particles inducing weathering spectral properties will accumulate at the surface of olivine and pyroxene minerals under heating conditions simulating micrometeorite impacts [3]. The skin depth of weathered material depends on theweathering process and minerals.Laboratory simulations by heating samples under reducing conditions can recreate the conditions under which regolith may be weathered inspace with surface alteration of grains and apparition of nanophase iron on the altered depth. The effect of the changes on the grain spectralproperties depending on the experimental conditions will be further studied for applications to airless bodies in the Solar System. The sampleswill be analyzed with SEM at IRAP and their reflectance spectra acquired with the SHADOWS instrument at IPAG [12] for future comparisonswith the spectra of Phobos and Deimos