Olivier Mousis

... Olivier; de Pater, Imke; Hammel, Heidi; Lisse, Carey; Edwards, Michelle; Sanchez-Lavega, Agustin; Simon-Miller, Amy; Yanamandra-Fisher ... Science Institute, Boulder, CO, USA), AF(Johns Hopkins University Applied Physics Laboratory, MD, USA), AG(Gemini South Observatory ...

Cette these est dediee a l'etude de l'origine de Titan et de son atmosphere. Dans l'hypothese ou la subnebuleuse de Saturne etait geometriquement mince, le modele de disque turbulent utilise, derive des travaux de Dubrulle (1993), est moins dense que le modele de Prinn et Fegley (1981). De ce fait, les conversions de Co en CH4 et de N2 en NH3 ont ete inhibees dans la subnebuleuse, contrairement a ce qui est couramment admis pour interpreter la presence du methane dans l'atmosphere de Titan. C'est pourquoi nous avons developpe un nouveau scenario de la formation de titan, qui tient compte simultanement des contraintes resultant de la chimie de la subnebuleuse et des abondances de CH4, N2 et CH3D mesurees dans l'atmosphere du satellite. Nous faisons l'hypothese que ces gaz proviennent initialement de la vaporisation du nuage presolaire, qui s'effondra et forma le Soleil et son disque environnant. Lors du refroidissement de la nebuleuse, les volatils auraient ete pieges sous formes de clathrates d'hydrates dans les grains, puis dans les planetesimaux qu'ils formerent. Les planetesimaux hydrates a l'origine de la formation de Titan seraient alors des rescapes de l'effondrement hydsrodynamique de la feeding zone de Saturne. Ce scenario a ete applique aux subnebuleuses de Jupiter et d'Uranus, et a apporte un certain nombre de contraintes sur la formation des satellites reguliers de ces planetes. Le temps et la zone de formation des grains cometaires ont egalement ete estimes dans la nebuleuse solaire. Enfin, l'etude experimentale de la temperature de fusion du dihydrate d'ammoniac dans la gamme des hautes pressions a apporte des nouvelles donnees thermodynamiques qui permettront d'ameliorer les modeles de l'interieur de Titan.

Using the clathrate hydrates trapping theory, we calculate the enrichments in volatiles in the atmospheres of Jupiter and Saturn from the thermodynamical evolution of the solar nebula, in a way consistent with recent models of giant planets formation (Alibert et al. 2005a). We also discuss the influence of the recent Cassini measurement of carbon abundance in Saturn (Flasar et al. 2005) on the amount of heavy elements required in the giant planet.

The 1.0m telescope at Sutherland (SAAO, South-Afrika) was used to image the objects (17493) WILDCAT, (22653) 1998 QW2, 2006 FZ51, 2006 GZ42, 2006 HH89. All of these asteroids have orbits with a Tisserand parameter close to 3, corresponding to the boundary between asteroidal and cometary orbits (Hsieh and Jewitt 2006 Science, 312, 561). Short exposure sequences of 30 to 60 seconds per frame were acquired between 2006-06-01 and 2006-06-11, giving a total exposure time of 45 to 60 minutes per object.

Using the clathrate hydrates trapping theory, we discuss the enrichments in volatiles in the atmosphere of Jupiter measured by the Galileo probe in the framework of new extended core accretion planet formation models including migration and disk evolution. We construct a self-consistent model in which the volatile content of planetesimals accreted during the formation of Jupiter is calculated from the thermodynamical evolution of the disk. Assuming CO2:CO:CH4=30:10:1 (ratios compatible with interstellar medium measurements), we show that we can explain the enrichments in volatiles in a way compatible with the recent constraints set from internal structure modeling on the total amount of heavy elements present in the planet.

Using a statistical model based on the theory of van der Waals and Platteeuw, we show that clathrate hydrates may influence the gas partionning in the atmosphere of Titan and Mars. Indeed, in January 2005, the atmospheric measurements carried out during the descent of the Huygens probe showed that, except for some tiny amounts of 36Ar, no other primordial noble gases were detected in Titan's atmosphere (their mole fractions may be smaller than the GCMS instrument's sensibility). It has been recently proposed that the formation of clathrate hydrates on the surface of Titan may act as a sink for atmospheric gases and that the trapping of noble gases in such hydrates can deeply modify their atmospheric concentration. The results of our calculations show that there is actually a strong correlation between the evolution of Titan's climate and the efficiency of the noble gases trapping in hydrates. Moreover, we find that, when the Titan's atmospheric temperature and pressure conditions decrease, the capture of Kr and Xe in hydrates becomes more efficient, whereas that of Ar diminishes. Moreover, recent observations have evidenced traces of methane (CH4) heterogeneously distributed in the Martian atmosphere. However, because the lifetime of CH4 in the atmosphere of Mars is estimated to be around 250-430 years on the basis of gas-phase chemistry, its actual sources on Mars remain controversial. Among other assumptions, it has been proposed that clathrate hydrates located in the subsurface of Mars could be at the origin of the small quantities of CH4 detected. Our results show that methane enriched clathrate hydrates could be stable in the subsurface of Mars only if a primitive CH4-rich atmosphere has existed or if a subsurface source of CH4 has been (or is still) present.

We present an evolutionary turbulent model of the Jovian subnebula consistent with the extended core accretion formation models of Jupiter described by Alibert et al. (2005a). We calculate the thermodynamical conditions inside the subnebula, and the migration of proto-satellites. By tempting to reproduce the location vs. ice content of the Jovian satellites, we obtain constraints on the dissipation parameter inside the subnebula.

We examine the implications of collisional effects on the physical and chemical differentiation of the planetesimals located in the primitive Edgeworth-Kuiper Belt. Results show changes in the initial composition only in the subsurface layers.

The trapping of volatile species in the form of clathrate hydrates during the formation of icy planetesimals in the outer solar nebula is a realistic mechanism to interpret the volatile enrichments observed in the giant planets. However, up until now, some ad hoc assumptions have been made in the scenarios using clathration as the main process to allow the trapping of volatiles in the solar nebula gas-phase. In particular, the clathration process is always assumed to be fully efficient. Moreover, the abundance of oxygen is still considered as a free parameter adjusted in order to provide enough water to trap as clathrate hydrate the required volatile species in the outer nebula. In this work, we address these shortcomings and we demonstrate that it is possible to fit the volatile enrichments in Jupiter and Saturn by postulating a partial efficiency of the clathration process and using an oxygen solar abundance. We also show that the volatile species that are not trapped via clathration crystallize as pure condensates at the temperature and pressure conditions of the outer solar nebula. Icy planetesimals formed in the outer nebula then incorporate volatiles trapped both in the form of clathrate hydrates and pure condensates. We finally show that the resulting quantities of volatiles contained within the envelopes of Jupiter and Saturn are compatible with the amounts of heavy elements (ices + rocks) predicted by their internal structure models.

We investigate here the sensitivity of gas hydrate occupancies predicted on the basis of van der Waals-Platteeuw theory, as a function of the treatment of the intermolecular guest-water interaction potential. First, we determine the minimum number of water molecules that have to be taken into account in the calculations of this interaction potential. We show that analytical correction terms that account for the interactions with the water molecules beyond the cutoff distance (typically chosen to take into account at least 4 water layers around the guest molecule) must be introduced to improve significantly the convergence rate, and hence the efficiency of the computation of the Langmuir constants. Then we use different recent guest-water interaction potential models to calculate the cage occupancies in pure methane or carbon dioxide clathrates. We show that the corresponding predicted cage occupancies can vary significantly depending on the model, although all the results are within the uncertainties of the available experimental data. That sensitivity becomes especially strong in the case of multiple guest clathrates, and, for instance, the results obtained for guest clathrate hydrates potentially formed on the surface of Mars can vary by more than two orders of magnitude depending on the model. These results underline the strong need for experimental data on pure and multiple guest clathrate hydrates, in particular in the temperature and pressure range that are relevant in extreme environment conditions, to discriminate among the theoretical models.

Comets have been considered to be representative of icy planetesimals that may have contributed a significant fraction of the volatile inventory of the terrestrial planets. For example, comets must have brought some water to Earth. However, the magnitude of their contribution is still debated. We report the detection of argon and its relation to the water abundance in the Jupiter family comet 67P/Churyumov-Gerasimenko by in situ measurement of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) mass spectrometer aboard the Rosetta spacecraft. Despite the very low intensity of the signal, argon is clearly identified by the exact determination of the mass of the isotope (36)Ar and by the (36)Ar/(38)Ar ratio. Because of time variability and spatial heterogeneity of the coma, only a range of the relative abundance of argon to water can be given. Nevertheless, this range confirms that comets of the type 67P/Churyumov-Gerasimenko cannot be the major source of Earth'...

In recent years, broadband colors on trans-Neptunian objects (TNOs) have greatly increased the knowledge of their surface properties. With the large and high quality color available datasets, strong and significant results have been found. We present here the last B-V, V-R and R-I color measurements obtained with the CFH12K mosaic camera of the 3.6m Canada-France-Hawaii Telescope (CFHT). This work is the latest extension of the Meudon Multicolor Survey (2MS) that totalizes now a dataset of 70 Centaurs and TNOs. In previous work (Doressoundiram et al., 2002, AJ, 124, 2279-2296), we found significant correlations between optical colors and some orbital parameters (i, e, q) for the Classical Kuiper Belt. On the other hand, no clear trend was obvious for Plutinos, Scattered objects or Centaurs. In this new and larger dataset, we looked for confirmation of the correlations found and possible detection of new significant trends for populations previously under sampled (e.g. scattered disk objects). We make also some comparison with related populations (e.g. irregular satellites, cometary nuclei). This analysis will be presented and discussed.

We calculate the structure and the evolution of the Saturn's subnebula, in a way consistent with the formation process of the planet, by using a two-dimensional evolutionary turbulent alpha-model. We also discuss the implications for the formation of Titan in the subnebula.

White Oval BA, constituted from 3 predecessor vortices (known as Jupiter's "classical" White Ovals) after successive mergers in 1998 and 2000, became second-largest vortex in the atmosphere of Jupiter (and possibly the solar system) at the time of its formation. While it continues in this distinction,it required a name change after a 2005 December through 2006 February transformation which made

We present analysis of thermal-infrared imaging and spectroscopy of the impact site near the south polar region of Jupiter (see Orton et al., AGU 2009). Enhanced thermal emission was first detected on July 20 2009 in 7-25 micron imaging from the MIRSI instrument on NASA's IRTF. These observations, just two rotations after the impact, indicated the localised, high-temperature thermal signature

Rising plumes and high temperature shocks resulting from collisions of primitive bodies with Jupiter produce dramatic perturbations to the atmospheric structure and chemistry. Spectroscopy of Jupiter's 7-25 µm spectrum, from NASA/IRTF, VLT and Gemini, demonstrates that these atmospheric perturbations differ substantially between impacts and can reveal the nature of the impactor. VLT/VISIR spectroscopy of the July 2009 impact site revealed

Observations of Jupiter were made between February and June of 2007 to provide an expanded spectral coverage and timeline for the New Horizons remote-sensing of Jupiter's atmosphere. From March to May, two prominent vertical jets in the southern portion of Jupiter's North Temperate Belt (NTBs) initiated a major darkening of this region, and their wakes restored the darker color of the belt but not its bright 5-micron appearance. A brightening of the southern component of the dark South Equatorial Belt (SEBs) was interrupted by a series of vertical outbursts from which a darker material emanated in both directions was appeared bright at 5 microns.It also generated a series of anticyclonic vortices with upwelling interiors and substantial downwelling annuli which continue to this writing.

Introduction: We investigate the interplay that would happen between a reservoir of liquid hydrocarbons located in Titan's subsurface and a hypothetical clath-rate reservoir that progressively forms when the liquid mixture diffuses throughout a coexisting porous icy layer. Hundreds of lakes and a few seas are observed to cover the polar regions of Titan [1]. While a significant number of these lakes and seas should be regularly filled by hydrocarbon rainfalls [2], some of them could be also renewed via their interconnection with liquid reservoirs of alkanes located in the subsurface [3]. These lakes could result from the interaction between subsurface liquid and clathrate reservoirs and possess a composition differing from that of lakes and rivers engendered by precipitations. As a liquid reservoir occupies a finite volume, the progressive transfer and fractionation of the molecules in the forming clathrate reservoir could alter the lakes' chemical composition. In order to e...

The European Space Agency has selected the Jupiter Icy Moons Explorer (JUICE) mission to fly to the Jupiter system and visit the moons Europa, Ganymede, and Callisto. One of the selected scientific instru-ments is the Particle Environment Package (PEP) that includes a Neutral gas and Ion mass spectrometer (NIM). NIM will measure the composition of the exospheres of these three moons during flybys and in orbit of Ganymede. Since all these exospheres are in direct contact with the surface of the respective moon, the chemical com-position of the surface can be inferred from of the exospheric measurements. Knowing the chemical composition of the surface, and accounting for radiation induced chemistry at and near the surface, one can compare with models of the formation of these icy satellites from the proto-planetary disk from which Jupiter and the icy moons formed. In addition, if the JUICE flyby trajectory allows sampling the recently discovered plume on Europa with NIM we can measure...

A comet's origins in the primitive nebula can be probed by examining the degree to which fossil deuterium is enriched compared to the protosolar abundance. Calculations of the temporal and radial evolution of the deuterium enrichment in the solar nebula can reproduce existing D/H measures for comets [1, 2, 3]. These calculations show that the deuterium enrichment in water ice strongly depends on the distance from the Sun at which the ice was formed. Comparing the D/H value measured in comets with those predicted by such models allows retrieval of their formation location. The measurement of the D/H ratio at Enceladus by the Ion and Neutral Mass Spectrometer aboard the Cassini spacecraft [4] provides a new, and tighter, constraint on the deuterium enrichment profile in the outer solar nebula prompting us to reconsider models presented in previous works [5].

In recent years, broadband colors on trans-Neptunian objects (TNOs) have greatly increased the knowledge of their surface properties. With the large and high quality color available datasets, strong and significant results have been found. We present here the last B-V, V-R and R-I color measurements obtained with the CFH12K mosaic camera of the 3.6m Canada-France-Hawaii Telescope (CFHT). This work is

ABSTRACT Amateur contributions to professional publications have increased exponentially over the last decades in the field of Planetary Astronomy. Here we review the different domains of the field in which collaborations between professional and amateur astronomers are effective and regularly lead to scientific publications. We discuss the instruments, detectors, softwares and methodologies typically used by amateur astronomers to collect the scientific data in the different domains of interest.

Multiple lines of evidence from the Cassini-Huygens mission demonstrate that Titan's large lakes and seas are composed of liquid ethane and methane. In addition to the aforementioned constituents, recent work on solubility indicates that propane, dissolved acetylene and nitriles will be significant components (Cordier, D. et al., ApJ v. 707, 128, 2009). Here we make a preliminary examination of the