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Depuis un demi-siècle, la planète Mars a été étudiée par de nombreuses missions spatiales : aux missions de survol ont succédé les orbiteurs, puis les modules de descente et les véhicules robotiques. Le lancement quasi simultané de trois nouvelles missions vers Mars, en juillet 2020, atteste de l'intérêt que porte à la planète la communauté scientifique, mais aussi le grand public. Le but ultime est la recherche de formes de vie, passée ou présente. Mais, au-delà de cet objectif, certains rêvent d'une exploration habitée de la planète, voire d'une « colonisation » humaine. Est-ce possible, et est-ce souhaitable ?

We have used infrared spectra of the dark side of Venus, recorded by the VIRTIS-H spectrometer (Drossart et al. Proc. SPIE 5543, 175, 2014) aboard Venus Express (Svedhem et al. JGR 113, E00B33, 2008), to analyze the CO (1-0) band around 4.7 µm. The resolving power of VIRTIS-H (about 1200) is sufficient to separate the individual lines of CO. We have selected two sets of spectra, the first one at mid-latitude (43°S) and the other in the polar collar (69-83°S). The CO individual lines appear in absorption in the first case, and in emission in the second case, as a consequence of a temperature inversion occurring at high latitude at the level of the upper cloud top. Synthetic models have been calculated using the Planetary Spectrum Generator (Villanueva et al. JQSRT 217, 86, 2018). Information is retrieved on the thermal vertical profile and the CO vertical distribution at both latitudes. This work illustrates the capabilities of high-resolution infrared spectroscopy for monitoring minor atmospheric species in the mesosphere of Venus, in the perspective of the EnVision mission (Helbert et al. Proc. SPIE 11128, A1112804, 2019).

Observed chemical species in the Venusian mesosphere show local-time variabilities. SO2 at the cloud top exhibits two local maxima over local time, H2O at the cloud top is uniformly distributed, and CO in the upper atmosphere shows a statistical difference between the two terminators. In this study, we investigated these local-time variabilities using a three-dimensional (3D) general circulation model (GCM) in combination with a two-dimensional (2D) chemical transport model (CTM). Our simulation results agree with the observed local-time patterns of SO2, H2O, and CO. The two-maximum pattern of SO2 at the cloud top is caused by the superposition of the semidiurnal thermal tide and the retrograde superrotating zonal (RSZ) flow. SO2 above 85 km shows a large day-night difference resulting from both photochemistry and the sub-solar to anti-solar (SS-AS) circulation. The transition from the RSZ flows to SS-AS circulation can explain the CO difference between two terminators and the displacement of the CO local-time maximum with respect to the anti-solar point. H2O is long-lived and exhibits very uniform distribution over space. We also present the local-time variations of HCl, ClO, OCS and SO simulated by our model and compare to the sparse observations of these species. This study highlights the importance of multidimensional CTMs for understanding the interaction between chemistry and dynamics in the Venusian mesosphere., Comment: 51 pages, 19 figures, accepted by Planetary Science Journal

1. IntroductionVenus is hosting a global sulfuric acid cloud layer between 45 and 70 km which has been investi- gated by the Venus Express and Akatsuki mission as well as its coupling with the surface. One of the main questions that remains unclear about the dynamics of the Venusian atmosphere is how this convective cloud layer mixes momentum, heat, and chemical species and generates gravity waves. Several models have been developed to study these phenomenons. We proposed to use these models to study the impact of this turbulence on the chemical species, focusing on water and sulfuric dioxide. 2. ModelTo study the convective layer, a Large Eddy Simulations (LES) model [1] has been developed using the Weather-Research Forecast (WRF) non-hydrostatic dynamical core [2] coupled with the IPSL Venus GCM physics package [3]. The model is able to resolve a realistic convective layer between 47 and 55 km as well as one convective layer at cloud top altitudes (70 km) at the substellar point (Fig 1). Figure 1: Vertical cross-section of the vertical wind (m/s) at the Equator at noon. Between 47 and 55 km is the main convective layer, between 55 and 67 km are the gravity waves induced by convection and between 67 and 73 is the cloud top convective layer presents only at the substellar point. Tracers has been included in the model representing H2O and SO2, the chemistry and photodissociation sources and sinks are modeled by a linear relaxation of the tracer abundance toward a prescribed vertical profile with a characteristic time. The relaxation time ranges from 102 to 106 s. The prescribed vertical tracer profiles are constructed using observed abundance visible in Fig 2. Figure 2: Vertical profile of the tracer abudance relaxation profile. The black represents the value for the deep atmosphre [4], the star is the SO2 ground based observations at 65 km [5] and the circle is the cloud top H2O Venus Express value [6, 7]. 3. ResultsThis simple model is able to determine the vertical mixing for SO2 and H2O in the cloud layer, and for which chemical timescale the convection plays an important role. The resolution of 500 m allow an estimate of the horizontal turbulent spatial features, induced by the convection and gravity waves, for SO2 and H2O. References[1] Lefèvre et al., JGR : Planets, 123, 2773-2789, 2018.[2] Skamarock, W. C. and J. B. Klemp, J., Comput. Phys., 227, 3465-3485, 2008[3] Garate-Lopez, I. and Lebonnois., S., Icarus, 314,1-11, 2018.[4] Bézard, B. and De Bergh, C., JGR : Planets, 112, 2007.[5] Encrenaz, T. et al., A. & A., 595, 2016.[6] Fedorova, A. et al., Icarus, 275, 143-162, 2016.[7] Cottini., V. et al., Icarus, 217, 561-569, 2012.

Ce chapitre décrit d’abord l’histoire de l’exploration des planètes géantes. Puis il présente une description globale des quatre planètes géantes, Jupiter, Saturne, Uranus et Neptune, en étudiant successivement les atmosphères, les structures internes et les magnétosphères.

Après une introduction historique, cette étude décrit les objets dénués d’atmosphère, Mercure et la Lune (paramètres orbitaux, exosphère, structure interne, surface, origine et, dans le cas de Mercure, magnétosphère). Puis elle présente une étude globale des trois planètes telluriques dotées d’une atmosphère (Vénus, la Terre et Mars) en traitant successivement l’intérieur, la surface, l’atmosphère et, dans le cas de Mars, les satellites.

Following the announcement of the detection of phosphine (PH$_3$) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the infrared range. Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO$_2$ and H$_2$O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm$^{-1}$ where a PH$_3$ transition is present. From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-$\sigma$ upper limit of 5 ppbv for the PH$_3$ mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths. Our result brings a strong constraint on the maximum PH$_3$ abundance at the cloud top and in the lower mesosphere of Venus., Comment: Astronomy & Astrophysics, in press

International audience; Following our previous work (Marcq et al., 2013, Marcq et al., 2011), we have updated our forward radiative transfer code and processed the whole SPICAV-UV/Venus Express nadir dataset (2006-2014) in order to retrieve SO2 abundance at cloud top – assuming a SO2 decreasing scale height of 3 km and a ratio SO/SO2 tied to 10% – as well as the imaginary index of scattering mode 1 particles, representative of the remaining UV absorption, since the OSSO vertical profile found by Frandsen et al. (2016) cannot account for our observations. Our main results mostly confirm and extend the validity of those discussed by Marcq et al. (2013), namely: (i) long-term variations of low latitude SO2 at 70 km between ∼ 100 ppbv (2007, 2009) and less than 10 ppbv (2014); (ii) in average, decreasing SO2 with increasing latitude and depletion near the sub-solar point, consistent with a competition between advection and photo-chemical destruction; (iii) secular increase of mode 1 imaginary index at 250 nm, from 10−2 to 5 ⋅ 10−2 between 2006 and 2010; (iv) if not related instead to long-term variability, a possible localized enrichment of SO2 and UV brightness increase above the western slopes of Aphrodite Terra, consistent with Bertaux et al. (2016) supply mechanism through orographic gravity waves. This spatial and temporal variability underlines the need for a long term monitoring of Venus SO2 and cloud top from ground-based facilities until the next generation of Venusian orbiters is operational.

We present a comparison of VLT-VISIR images and Keck-NIRC2 images of Neptune, which highlight the coupling between its troposphere and stratosphere. VLT-VISIR images were obtained on September 16th 2008 (UT) at 7.90 μ m and 12.27 μ m, which are primarily sensitive to 1-mbar CH 4 and C 2 H 6 emission, respectively. NIRC2 images in the H band were obtained on October 5th, 6th and 9th 2008 (UT) and sense clouds and haze in the upper troposphere and lower stratosphere (from approximately 600 to 20 mbar). At 7.90 μ m, we observe enhancements of CH 4 emission in latitude bands centered at approximately 25 ∘ S and 48 ∘ S (planetocentric). Within these zonal bands, tentative detections ( 2 σ ) of discrete hotspots of CH 4 emission are also evident at 24 ∘ S, 181 ∘ W and 42 ∘ S, 170 ∘ W. The longitudinal-mean enhancements in the CH 4 emission are also latitudinally-coincident with bands of bright (presumably CH 4 ice) clouds in the upper troposphere and lower stratosphere evidenced in the H-band images. This suggests the Neptunian troposphere and stratosphere are coupled in these specific regions. This could be in the form of (1) ‘overshoot’ of strong, upwelling plumes and advection of CH 4 ice into the lower stratosphere, which subsequently sublimates into CH 4 gas and/or (2) generation of waves by plumes impinging from the tropopause below, which impart their energy and heat the lower stratosphere. We favor the former process since there is no evidence of similar smaller-scale morphology in the C 2 H 6 emission, which probes a similar atmospheric level. However, we cannot exclude temperature variations as the source of the morphology observed in CH 4 emission. Future, near-infrared imaging of Neptune performed near-simultaneously with future mid-infrared spectral observations of Neptune by the James Webb Space Telescope would allow the coupling of Neptune’s troposphere and stratosphere to be confirmed and studied in greater detail.

International audience; Several temperate Jupiters have been discovered to date, but most of them remain to be detected. In this note, we analyse the expected infrared transmission spectrum of a temperate Jupiter, with an equilibrium temperature ranging between 350 and 500 K. We estimate its expected amplitude signal through a primary transit, and we analyse the best conditions for the host star to be filled in order to optimize the S/N ratio of its transmission spectrum. Calculations show that temperate Jupiters around M stars could have an amplitude signal higher than 10−4 in primary transits, with revolution periods of a few tens of days and transit durations of a few hours. In order to enlarge the sampling of exoplanets to be observed with ARIEL (presently focussed on objects warmer than 500 K), such objects could be considered as additional possible targets for the mission.

The global D/H ratio on Mars is an important measurement for understanding the past history of water on Mars; locally, through condensation and sublimation processes, it is a possible tracer of the sources and sinks of water vapor on Mars. Measuring D/H as a function of longitude, latitude and season is necessary for determining the present averaged value of D/H on Mars. Following an earlier measurement in April 2014, we used the Echelon Cross Echelle Spectrograph (EXES) instrument on board the Stratospheric Observatory for Infrared Astronomy (SOFIA) facility to map D/H on Mars on two occasions, on March 24, 2016 (Ls = 127°), and January 24, 2017 (Ls = 304°), by measuring simultaneously the abundances of H2O and HDO in the 1383–1391 cm−1 range (7.2 μm). The D/H disk-integrated values are 4.0 (+0.8, −0.6) × Vienna Standard Mean Ocean Water (VSMOW) and 4.5 (+0.7, −0.6) × VSMOW, respectively, in agreement with our earlier result. The main result of this study is that there is no evidence of strong local variations in the D/H ratio nor for seasonal variations in the global D/H ratio between northern summer and southern summer.

The germane molecule, GeH4, is present in the atmospheres of giant planets Jupiter and Saturn. The ongoing NASA mission Juno has renewed interest in its spectroscopy, whose accurate modeling is essential for the retrieval of other tropospheric species. We present here the first complete analysis and modeling of line positions and intensities in the strongly absorbing ν1/ν3 stretching dyad region near 2100 cm − 1 , for all five germane isotopologues in natural abundance. New infrared spectra were recorded, absolute intensities were extracted through a careful procedure and modeled thanks to the formalism and programs developed in the Dijon group. A database of calculated germane lines, GeCaSDa, has been build and is available online through the Virtual Atomic and Molecular Data Centre (VAMDC) portal and at http://vamdc.icb.cnrs.fr/PHP/gecasda.php .

High-resolution ( R ~ 43 , 000 ) spectroscopic observations of both day and night sides of Venus were acquired using CSHELL at IRTF between 2202 and 2207 cm − 1 (4.53– 4.54 μ m ) during the latest maximal eastern and western elongations of Venus in two four-nights observing runs in August 2012 and November 2013. Their purpose was to investigate the effect of the recent (from 2007 onwards) decrease of sulfur dioxide (SO2) at the cloud top level on the spatial distribution of carbon monoxide (CO), since both species are involved in the mesospheric photochemical cycles. Observations of neighboring CO2 lines are fully consistent with the previously determined aerosol scale height in the 68–74 km range. We could therefore determine CO mixing ratio on both day and night sides of Venus, taking into account both scattered solar and thermal components, as well as the overlying CO dayglow on the day side. CO spatial distribution is mostly unchanged compared to previous measurements, ranging from 25 ppmv to 45 ppmv at 70 km. The scattered solar component reveals an increase in CO with increasing altitude with a scale height of ( 5 ± 0.5 ) km between 70 and 76 km. Horizontal variability is found to be weak, with a possible increase towards higher latitudes on the day side of about 10 ppmv. Yet the accuracy of our absolute values of CO mixing ratio is limited by several assumptions, and we cannot rule out that some of the variability we measure for CO could alternatively be explained by other changes occurring in the Venusian atmosphere, e.g. changes in both dT/dz and aerosol scale height.

Millimeter and submillimeter heterodyne spectroscopy offers the possibility of probing the mesosphere of Venus and monitoring minor species and winds. ALMA presents a unique opportunity to map mesospheric species of Venus. During Cycle 0, we have observed Venus on November 14 and 15, 2011, using the compact configuration of ALMA. The diameter of Venus was 11″ and the illumination factor was about 90%. Maps of CO, SO, SO 2 and HDO have been built from transitions recorded in the 335–347 GHz frequency range. A mean mesospheric thermal profile has been inferred from the analysis of the CO transition at the disk center, to be used in support of minor species retrieval. Maps of SO and SO 2 abundance show significant local variations over the disk and contrast variations by as much as a factor 4. In the case of SO 2 , the spatial distribution appears more “patchy”, i.e. shows short-scale structures apparently disconnected from day-side and latitudinal variations. For both molecules, significant changes occur over a timescale of one day. From the disk averaged spectrum of SO recorded on November 14 at 346.528 GHz, we find that the best fit is obtained with a cutoff in the SO vertical distribution at 88±2 km and a uniform mixing ratio of 8.0±2.0 ppb above this level. The SO 2 map of November 14, derived from the weaker transition at 346.652 GHz, shows a clear maximum in the morning side at low latitudes, which is less visible in the map of November 15. We find that the best fit for SO 2 is obtained for a cutoff in the vertical distribution at 88±3 km and a uniform mixing ratio of 12.0±3.5 ppb above this level. The HDO maps retrieved from the 335.395 GHz show some enhancement in the northern hemisphere, but less contrasted variations than for the sulfur species maps, with little change between November 14 and 15. Assuming a typical D/H ratio of 200 times the terrestrial value in the mesosphere of Venus, we find that the disk averaged HDO spectrum is best fitted with a uniform H 2 O mixing ratio of 2.5±0.6 ppm (corresponding to a HDO mixing ratio of 0.165±0.040 ppm). We note that our spectrum is also compatible with a H 2 O mixing ratio of 1.5 ppm in the 80–90 km altitude range, and a mixing ratio of 3 ppm outside this range, as suggested by the photochemical model of Zhang et al. (2012, Icarus , vol. 217, pp. 714–739). Our results are in good general agreement with previous single dish submillimeter observations of Sandor and Clancy (2005, Icarus , vol. 177, pp. 129–143), Gurwell et al. (2007, Icarus , vol. 188, p. 288), and Sandor et al. (2010, Icarus , vol. 208, pp. 49–60; 2012, Icarus, vol. 217, pp. 839–844 ) and with SPICAV/Venus Express results of Fedorova et al. (2008, J. Geophys. Res. , vol. 113, p. E00B25) and Belyaev et al. (2012).

International audience

Context. Water vapor and sulfur compounds are key species in the photochemistry of Venus mesosphere. These species, together with mesospheric temperatures, exhibit drastic temporal variations, both on short timescales (diurnal and day-to-day) as well on long timescales, far from being understood. Aims. We targeted CO, SO, HDO and SO 2 transitions in the submillimeter range using the Atacama Large Millimeter Array (ALMA) to study their spatial and temporal variations. Methods. Four sets of observations were acquired on different dates in November 2011 during the first ALMA Early Science observation Cycle 0. Venus angular diameter was about 11′′ with an illumination factor of 92%, so that mostly the day side of the planet was mapped. Assuming a nominal CO abundance profile, we retrieved vertical temperature profiles over the entire disk as a function of latitude and local time. Temperature profiles were later used to retrieve SO, SO 2 , and H 2 O. We used HDO as a tracer for water assuming a D/H enrichment of 200 times the terrestrial value. Results. We derived 3D maps of mesospheric temperatures in the altitude range 70−105 km. SO, SO 2 , and H 2 O are characterized by a negligible abundance below ~ 85 km followed by an increase with altitude in the upper mesosphere. Disk-averaged SO abundances present a maximum mixing ratio of 15.0 ± 3.1 ppb on November 26 followed the next day by a minimum value of 9.9 ± 1.2 ppb. Due to a very low S/N, SO 2 could only be derived from the disk-averaged spectrum on the first day of observation revealing an abundance of 16.5 ± 4.6 ppb. We found a SO 2 /SO ratio of 1.5 ± 0.4. Global maps of SO reveal strong variations both with latitude and local time and from day to day with abundance ranging from 2 O disk-averages retrievals reveal a steady decrease from November 14 to 27, with the abundance varying from 3.6 ± 0.6 ppm on the first day to 2.9 ± 0.7 ppm on the last day. H 2 O maps reveal a slightly higher abundance on the evening side compared to the morning side and a strong depletion between the first and the second day of observation.

International audience; The vertical distribution of sulfur species in the Venus atmosphere has been investigated and discussed in Part I of this series of papers dealing with the variability of SO2 on Venus. In this second part, we focus our attention on the spatial (horizontal) and temporal variability exhibited by SO2. Appropriate data sets – SPICAV/UV nadir observations from Venus Express, ground-based ALMA and TEXES, as well as UV observation on the Hubble Space Telescope – have been considered for this analysis. High variability both on short-term and short-scale are observed. The long-term trend observed by these instruments shows a succession of rapid increases followed by slow decreases in the SO2 abundance at the cloud top level, implying that the transport of air from lower altitudes plays an important role. The origins of the larger amplitude short-scale, short-term variability observed at the cloud tops are not yet known but are likely also connected to variations in vertical transport of SO2 and possibly to variations in the abundance and production and loss of H2O, H2SO4, and Sx.

International audience; A scientific forum on "The Future Science of Exoplanets and Their Systems," sponsored by Europlanet* and the International Space Science Institute (ISSI)† and co-organized by the Center for Space and Habitability (CSH)‡ of the University of Bern, was held during December 5 and 6, 2012, in Bern, Switzerland. It gathered 24 well-known specialists in exoplanetary, Solar System, and stellar science to discuss the future of the fast-expanding field of exoplanetary research, which now has nearly 1000 objects to analyze and compare and will develop even more quickly over the coming years. The forum discussions included a review of current observational knowledge, efforts for exoplanetary atmosphere characterization and their formation, water formation, atmospheric evolution, habitability aspects, and our understanding of how exoplanets interact with their stellar and galactic environment throughout their history. Several important and timely research areas of focus for further research efforts in the field were identified by the forum participants. These scientific topics are related to the origin and formation of water and its delivery to planetary bodies and the role of the disk in relation to planet formation, including constraints from observations as well as star-planet interaction processes and their consequences for atmosphere-magnetosphere environments, evolution, and habitability. The relevance of these research areas is outlined in this report, and possible themes for future ISSI workshops are identified that may be proposed by the international research community over the coming 2-3 years.

Aims: Disk-averaged infrared spectra of Neptune between 1.8 and 13 $\mu$m, obtained by the AKARI Infrared Camera (IRC) in May 2007, have been analysed to (a) determine the globally-averaged stratospheric temperature structure; (b) derive the abundances of stratospheric hydrocarbons; and (c) detect fluorescent emission from CO at 4.7 $\mu$m. Methods: Mid-infrared spectra were modelled using a line-by-line radiative transfer code to determine the temperature structure between 1-1000 $\mu$bar and the abundances of CH$_4$, CH$_3$D and higher-order hydrocarbons. A full non-LTE radiative model was then used to determine the best fitting CO profile to reproduce the fluorescent emission observed at 4.7 $\mu$m in the NG channel (with a spectral resolution of 135). Results: The globally-averaged stratospheric temperature structure is quasi-isothermal between 1-1000 $\mu$bar, which suggests little variation in global stratospheric conditions since studies by the Infrared Space Observatory a decade earlier. The derived CH$_4$ mole fraction of $(9.0\pm3.0)\times10^{-4}$ at 50 mbar, decreasing to $(0.9\pm0.3)\times10^{-4}$ at 1 $\mu$bar, is larger than that expected if the tropopause at 56 K acts as an efficient cold trap, but consistent with the hypothesis that CH$_4$ leaking through the warm south polar tropopause (62-66 K) is globally redistributed by stratospheric motion. The ratio of D/H in CH$_4$ of $3.0\pm1.0\times10^{-4}$ supports the conclusion that Neptune is enriched in deuterium relative to the other giant planets. We determine a mole fraction of ethane of $(8.5\pm2.1)\times10^{-7}$ at 0.3 mbar, consistent with previous studies, and a mole fraction of ethylene of $5.0_{-2.1}^{+1.8}\times10^{-7}$ at 2.8 $\mu$bar. An emission peak at 4.7 $\mu$m is interpreted as a fluorescent emission of CO, and requires a vertical distribution with both external and internal sources of CO., Comment: In press, accepted manuscript

International audience; On a planetary scale, the D/H ratio on Mars is a key diagnostic for understanding the past history of water on the planet; locally, it can help to constrain the sources and sinks of water vapor through the monitoring of condensation and sublimation processes. To obtain simultaneous measurements of H2O and HDO lines, we have used the Echelle Cross Echelle Spectrograph (EXES) instrument aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) facility to map the abundances of these two species over the Martian disk. High-resolution spectra (R = 6 × 104) were recorded in the 1383−1390 cm-1 range (7.2 μm) on April 08, 2014. Mars was very close to opposition and near northern summer solstice (Ls = 113°). Maps of the H2O and HDO mixing ratios were retrieved from the line depth ratios of weak H2O and HDO transitions divided by a weak CO2 line. As expected for this season, the H2O and HDO maps show a distinct enhancement toward polar regions, and their mixing ratios are consistent with previous measurements and with predictions by the global climate models, except at the north pole where the EXES values are weaker. We derive a disk-integrated D/H ratio of 6.8 (+1.6, −1.0) × 10-4. It is higher than the value in Earth’s oceans by a factor 4.4 (+1.0, −0.6). The D/H map also shows an enhancement from southern to northern latitudes, with values ranging from about 3.5 times to 6.0 times the VSMOW (Vienna standard mean ocean water) value. The D/H distribution shows a depletion over the Tharsis mountains and is consistent with observed latitudinal variations. The variations in D/H with latitude and altitude agree with the models and with the isotope fractionation expected from condensation and sublimation processes.

In this paper, we summarize the main capabilities of the James Webb Space Telescope (JWST) for performing observations of Mars. The distinctive vantage point of JWST at the Sun-Earth Lagrange point (L2) will allow sampling the full observable disk, permitting the study of short-term phenomena, diurnal processes (across the east-west axis), and latitudinal processes between the hemispheres (including seasonal effects) with excellent spatial resolutions (0.''07 at 2 micron). Spectroscopic observations will be achievable in the 0.7-5 micron spectral region with NIRSpec at a maximum resolving power of 2700 and with 8000 in the 1-1.25 micron range. Imaging will be attainable with the Near-Infrared Camera at 4.3 micrometers and with two narrow filters near 2 micron, while the nightside will be accessible with several filters in 0.5 to 2 micron. Such a powerful suite of instruments will be a major asset for the exploration and characterization of Mars. Some science cases include the mapping of the water D/H ratio, investigations of the Martian mesosphere via the characterization of the non-local thermodynamic equilibrium CO2 emission at 4.3 micron, studies of chemical transport via observations of the O2 nightglow at 1.27 micron, high-cadence mapping of the variability dust and water-ice clouds, and sensitive searches for trace species and hydrated features on the Martian surface. In-flight characterization of the instruments may allow for additional science opportunities.

L’exploration de la planete Mars, entreprise par les astronomes des l’apparition de la lunette de Galilee au debut du XVIIe siecle, a vecu un nouvel essor avec l’avenement de l’exploration spatiale au cours des annees 1960. Plus petite et plus froide que la Terre, Mars a sans doute connu au debut de son histoire une atmosphere plus dense, plus chaude et plus humide qu’aujourd’hui, susceptible d’abriter l’eau liquide. Puis la planete a vu son activite interne decroitre avant la fin du premier milliard d’annees, et son atmosphere s’est rarefiee. Aujourd’hui, Mars est plus que jamais au coeur de l’exploration planetaire; l’enjeu est de determiner si la vie a pu apparaitre au debut de son histoire et si nous pouvons esperer y decouvrir un jour des traces de vie fossile.

International audience; Using TEXES, the Texas Echelon cross Echelle Spectrograph, mounted on the Gemini North 8-m telescope we have mapped the spatial variation of H 2, CH 4, C 2H 2 and C 2H 6 thermal-infrared emission of Neptune. These high-spectral-resolution, spatially resolved, thermal-infrared observations of Neptune offer a unique glimpse into the state of Neptune's stratosphere in October 2007, LS = 275.4° just past Neptune's southern summer solstice ( LS = 270°). We use observations of the S(1) pure rotational line of molecular hydrogen and a portion of the nu4 band of methane to retrieve detailed information on Neptune's stratospheric vertical and meridional thermal structure. We find global-average temperatures of 163.8 ± 0.8, 155.0 ± 0.9, and 123.8 ± 0.8 K at the 7.0 × 10 -3-, 0.12-, and 2.1-mbar levels with no meridional variations within the errors. We then use the inferred temperatures to model the emission of C 2H 2 and C 2H 6 in order to derive stratospheric volume mixing ratios (hence forth, VMR) as a function of pressure and latitude. There is a subtle meridional variation of the C 2H 2 VMR at the 0.5-mbar level with the peak abundance found at -28° latitude, falling off to the north and south. However, the observations are consistent within error to a meridionally constant C 2H 2 VMR of 3.3-0.9+1.2×10-8 at 0.5 mbar. We find that the VMR of C 2H 6 at 1-mbar peaks at the equator and falls by a factor of 1.6 at -70° latitude. However, a meridionally constant VMR of 9.3-2.6+3.5×10-7 at the 1-mbar level for C 2H 6 is also statistically consistent with the retrievals. Temperature predictions from a radiative-seasonal climate model of Neptune that assumes the hydrocarbon abundances inferred in this paper are lower than the measured temperatures by 40 K at 7 × 10 -3 mbar, 30 K at 0.12 mbar and 25 K at 2.1 mbar. The radiative-seasonal model also predicts meridional temperature variations on the order of 10 K from equator to pole, which are not observed. Assuming higher stratospheric CH 4 abundance at the equator relative to the south pole would bring the meridional trends of the inferred temperatures and radiative-seasonal model into closer agreement. We have also retrieved observations of C 2H 4 emission from Neptune's stratosphere using TEXES on the NASA Infrared Telescope Facility (IRTF) in June 2003, LS = 266°. Using the observations from the middle of the planet and an average of the middle three latitude temperature profiles from the 2007 observations (9.5° of LS later, the seasonal equivalent of 9.5 Earth days within Earth's seasonal cycle), we infer a C 2H 4 VMR of 5.9-0.8+1.0×10-7 at 1.5 × 10 -3 mbar, a value that is 3.25 times that predicted by global-average photochemical models.

Discovery of CH4 in the Martian atmosphere has led to much discussion since it could be a signature of biological and/or geological activities on Mars. However, the presence of CH4 and its temporal and spatial variations are still under discussion because of the large uncertainties embedded in the previous observations. We performed sensitive measurements of Martian CH4 by using the Echelon-Cross-Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) on 16 March 2016, which corresponds to summer (Ls = 123.2∘) in the northern hemisphere on Mars. The high altitude of SOFIA (~13.7 km) enables us to significantly reduce the effects of terrestrial atmosphere. Thanks to this, SOFIA/EXES improves our chances of detecting Martian CH4 lines because it reduces the impact of telluric CH4 on Martian CH4, and allows us to use CH4 lines in the 7.5 μm band which has less contamination. However, our results show no unambiguous detection of Martian CH4. The Martian disk was spatially resolved into 3 × 3 areas, and the upper limits on the CH4 volume mixing ratio range from 1 to 9 ppb across the Martian atmosphere, which is significantly less than detections in several other studies. These results emphasize that release of CH4 on Mars is sporadic and/or localized if the process is present.

The four giant planets - Jupiter, Saturn, Uranus and Neptune - have common properties which make them very different from the terrestrial planets: located at large distances from the Sun, they have big sizes and masses but low densities; they all have a ring system and a large number of satellites. These common properties can be understood in the light of their formation scenario, based upon the accretion of protosolar gas on an initial icy core. Giant planets have been explored by space missions (Pioneer 10 and 11, Voyager 1 and 2, Galileo and Cassini) but also by Earth-orbiting satellites and ground-based telescopes. There are still open questions related to the origin and evolution of the giant planets, in particular their moderate migration, the origin of the cold planetesimals which formed Jupiter, the origin of the atmospheric dynamics in Jupiter and Saturn, and the differences in the internal structures of Uranus and Neptune.