We have used recent surveys of the composition of exoplanet host stars to investigate the expecte... more We have used recent surveys of the composition of exoplanet host stars to investigate the expected composition of condensed material in planetesimals formed beyond the snow line in the circumstellar nebulae of these systems. Of the major solid-forming elements, C and O abundances (and particularly the C/O abundance ratio) strongly affect the amounts of volatile ices and refractory phases in icy planetesimals formed in these systems. This results from these elements' effects on the partitioning of O among gas, refractory solid and ice phases in the final condensate. The calculations use a self-consistent model for the condensation sequence of volatile ices from the nebula gas after refractory (silicate and metal) phases have condensed. The resultant mass fractions (compared to the total condensate) of refractory phases and ices were calculated for a range of nebular temperature structures and redox conditions. Planetesimals in systems with sub-solar C/O should be water ice-rich, with lower than solar mass fractions of refractory materials, while in super-solar C/O systems planetesimals should have significantly higher mass fractions of refractories, in some cases having little or no water ice. C-bearing volatile ices and clathrates also become increasingly important with increasing C/O depending on the assumed nebular temperatures. These compositional variations in early condensates in the outer portions of the nebula will be significant for the equivalent of the Kuiper Belt in these systems, icy satellites of giant planets, and the enrichment (over stellar values) of volatiles and heavy elements in giant planet atmospheres.
We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.... more We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5 and 8 µm obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. After correcting for systematic effects of the instrument, we fitted the light curves -including limb darkening effects -using the Markov Chain Monte Carlo technique. The robustness of our reduction methods was then tested by adopting the Bayesian Information Criterion. The final transit depth measurements obtained are 0.712±0.006%, 0.638±0.018%, and 0.692±0.007% respectively, at 3.6 µm, 4.5 µm, and 8 µm. Combining these new data with the EPOXI, HST and groundbased V, I, H and K s observations available in the literature, the range 0.5 − 10 µm can be covered. A possible source of systematic errors when combining data taken over different epochs and in different bands is the influence of magnetic activity, i.e. starspots. To test that possibility, an accurate study of the star was performed; due to the low activity level of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the dataset, well below our typical transit depth measurement error. The temperature distribution of the planet was estimated by using a three-dimensional, pseudo-spectral general circulation model with idealised thermal forcing. Transmission spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the molecular species expected to be present in such planetary atmosphere, namely water vapour, methane, Methane in the atmosphere of the transiting hot Neptune GJ436b? 2 ammonia, carbon monoxide and dioxide, and hydrogen sulphide. In particular, a new, ab-initio calculated, linelist for hot ammonia has been used for the first time. The photometric data observed at multiple wavelengths can be interpreted with methane being the dominant species after molecular hydrogen, possibly with minor contributions from ammonia, water and other molecules. No clear evidence of carbon monoxide and dioxide is found from transmission photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesised to interpret secondary transit photometric data. In particular we show that the emission photometric data are not incompatible with the presence of abundant methane, but further spectroscopic data are desirable to confirm this scenario.
Kuiper Belt Objects and cometary nuclei are considered among the most pristine bodies of the oute... more Kuiper Belt Objects and cometary nuclei are considered among the most pristine bodies of the outer Solar system. However, the composition of these objects might not reflect that of the planetesimals from which they accreted. They have experienced some collisional activity since the formation of the Edgeworth-Kuiper Belt, leading to a possible alteration of their structure and composition. Here, we examine the possible alteration of icy bodies (10 to 100 km radii) located in the primitive Edgeworth-Kuiper Belt due to the heat generated by collisions of planetesimals with sizes not exceeding 10 per cent of the target body. We use a cometary nucleus model initially made of a mixture of amorphous ice and dust to investigate the influence of the target's intrinsic properties on its post-impact thermodynamical evolution. We show that multiple collisions must be considered over long periods to trigger a continuous crystallization within a target owning a typical cometary composition. However, the collision rates we have determined are approximately 1000 times greater than those predicted for the current collisional environment in the Edgeworth-Kuiper Belt. This implies that the collisional processes that occurred over the age of the Solar system did not produce any phase transition of H 2 O ice from amorphous to crystalline forms in cometary size bodies located in the primitive Edgeworth-Kuiper Belt.
Mid-infrared 7–20μm imaging of Jupiter from ESO’s Very Large Telescope (VLT/VISIR) demonstrate th... more Mid-infrared 7–20μm imaging of Jupiter from ESO’s Very Large Telescope (VLT/VISIR) demonstrate that the increased albedo of Jupiter’s South Equatorial Belt (SEB) during the ‘fade’ (whitening) event of 2009–2010 was correlated with changes to atmospheric temperature and aerosol opacity. The opacity of the tropospheric condensation cloud deck at pressures less than 800mbar increased by 80% between May 2008 and July
This report is the follow-up of the paper of A. Drouart et al. (1999, Icarus 140, 129) in which i... more This report is the follow-up of the paper of A. Drouart et al. (1999, Icarus 140, 129) in which it was demonstrated that appropriate models of the solar nebula permit us to interpret the deuterium enrichment in water with respect to the protosolar D/H ratio measured in LL3 meteorites and comets. In the present report, we show that the models selected by Drouart et al. are also able to explain D/H in HCN measured in Comet C/1995 O1 (Hale-Bopp). We find that the D/H ratio in HCN entering the nebula is ∼4 × 10 −3 , which is significantly less than values measured in cold dark clouds, but consistent with values found in hot molecular cores. Both H 2 O and HCN ices infalling from the presolar cloud onto the nebula discoid evaporated in the turbulent part of the nebula, isotopically exchanged with hydrogen, and mixed with water vapor coming from the inner part of the nebula. Subsequently, H 2 O and HCN ices with D/H ratios measured in Comet Hale-Bopp condensed, agglomerated and were incorporated in cometesimals. In the light of these results, we discuss the story of molecules detected in comets coming from Oort cloud. Most molecules detected in Comet Hale-Bopp originated from ices embedded in the presolar cloud. Ices vaporized prior to entering into the nebula or in the early nebula, and subsequently recondensed, except highly volatile molecules. According to A. Kouchi et al. (1994, Astron. Astrophys. 290, 1009), water ice condensed in crystalline form. We discuss the possibility that the most volatile species were then trapped in the form of clathrate hydrates. The oversolar C/N ratio and the strong depletion of Ne/O with respect to the solar abundance observed in comets are in agreement with the theory of clathrate hydrates of J. I. Lunine and D. J. . Comets formed in the Kuiper belt may contain amorphous water ice and have kept the isotopic signature of the presolar cloud. New published models of interiors of Uranus and Neptune permit us to calculate that the D/H ratios in proto-uranian and protoneptunian water ices are in agreement with those measured in comets. This confirms the current assumption that cometesimals and planetesimals that formed the cores of Uranus and Neptune had similar compositions.
Protoplanetary disks start their lives with a dust free inner region where the temperatures are h... more Protoplanetary disks start their lives with a dust free inner region where the temperatures are higher than the sublimation temperature of solids. As the star illuminates the innermost particles, which are immersed in gas at the sublimation edge, these particles are subject to a photophoretic force. We examine the motion of dust particles at the inner edge of protoplanetary disks
We study the formation conditions of icy planetesimals in protoplanetary disks in order to determ... more We study the formation conditions of icy planetesimals in protoplanetary disks in order to determine the composition of ices in small and cold extrasolar planets. Assuming that ices are formed from hydrates, clathrates, and pure condensates, we calculate their mass fractions with respect to the total quantity of ices included in planetesimals, for a grid of disk models. We find that the composition of ices weakly depends on the adopted disk thermodynamic conditions, and is rather influenced by the initial composition of the gas phase. The use of a plausible range of molecular abundance ratios and the variation of the relative elemental carbon over oxygen ratio in the gas phase of protoplanetary disks allow us to apply our model to a wide range of planetary systems. Our results can thus be used to constrain the icy/volatile phase composition of cold planets evidenced by microlensing surveys, hypothetical ocean planets, and carbon planets, which could be detected by COROT or Kepler. Subject headingg s: planetary systems -planetary systems: formation
We have used recent surveys of the composition of exoplanet host stars to investigate the expecte... more We have used recent surveys of the composition of exoplanet host stars to investigate the expected composition of condensed material in planetesimals formed beyond the snow line in the circumstellar nebulae of these systems. Of the major solid-forming elements, C and O abundances (and particularly the C/O abundance ratio) strongly affect the amounts of volatile ices and refractory phases in icy planetesimals formed in these systems. This results from these elements' effects on the partitioning of O among gas, refractory solid and ice phases in the final condensate. The calculations use a self-consistent model for the condensation sequence of volatile ices from the nebula gas after refractory (silicate and metal) phases have condensed. The resultant mass fractions (compared to the total condensate) of refractory phases and ices were calculated for a range of nebular temperature structures and redox conditions. Planetesimals in systems with sub-solar C/O should be water ice-rich, with lower than solar mass fractions of refractory materials, while in super-solar C/O systems planetesimals should have significantly higher mass fractions of refractories, in some cases having little or no water ice. C-bearing volatile ices and clathrates also become increasingly important with increasing C/O depending on the assumed nebular temperatures. These compositional variations in early condensates in the outer portions of the nebula will be significant for the equivalent of the Kuiper Belt in these systems, icy satellites of giant planets, and the enrichment (over stellar values) of volatiles and heavy elements in giant planet atmospheres.
We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.... more We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5 and 8 µm obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. After correcting for systematic effects of the instrument, we fitted the light curves -including limb darkening effects -using the Markov Chain Monte Carlo technique. The robustness of our reduction methods was then tested by adopting the Bayesian Information Criterion. The final transit depth measurements obtained are 0.712±0.006%, 0.638±0.018%, and 0.692±0.007% respectively, at 3.6 µm, 4.5 µm, and 8 µm. Combining these new data with the EPOXI, HST and groundbased V, I, H and K s observations available in the literature, the range 0.5 − 10 µm can be covered. A possible source of systematic errors when combining data taken over different epochs and in different bands is the influence of magnetic activity, i.e. starspots. To test that possibility, an accurate study of the star was performed; due to the low activity level of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the dataset, well below our typical transit depth measurement error. The temperature distribution of the planet was estimated by using a three-dimensional, pseudo-spectral general circulation model with idealised thermal forcing. Transmission spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the molecular species expected to be present in such planetary atmosphere, namely water vapour, methane, Methane in the atmosphere of the transiting hot Neptune GJ436b? 2 ammonia, carbon monoxide and dioxide, and hydrogen sulphide. In particular, a new, ab-initio calculated, linelist for hot ammonia has been used for the first time. The photometric data observed at multiple wavelengths can be interpreted with methane being the dominant species after molecular hydrogen, possibly with minor contributions from ammonia, water and other molecules. No clear evidence of carbon monoxide and dioxide is found from transmission photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesised to interpret secondary transit photometric data. In particular we show that the emission photometric data are not incompatible with the presence of abundant methane, but further spectroscopic data are desirable to confirm this scenario.
Kuiper Belt Objects and cometary nuclei are considered among the most pristine bodies of the oute... more Kuiper Belt Objects and cometary nuclei are considered among the most pristine bodies of the outer Solar system. However, the composition of these objects might not reflect that of the planetesimals from which they accreted. They have experienced some collisional activity since the formation of the Edgeworth-Kuiper Belt, leading to a possible alteration of their structure and composition. Here, we examine the possible alteration of icy bodies (10 to 100 km radii) located in the primitive Edgeworth-Kuiper Belt due to the heat generated by collisions of planetesimals with sizes not exceeding 10 per cent of the target body. We use a cometary nucleus model initially made of a mixture of amorphous ice and dust to investigate the influence of the target's intrinsic properties on its post-impact thermodynamical evolution. We show that multiple collisions must be considered over long periods to trigger a continuous crystallization within a target owning a typical cometary composition. However, the collision rates we have determined are approximately 1000 times greater than those predicted for the current collisional environment in the Edgeworth-Kuiper Belt. This implies that the collisional processes that occurred over the age of the Solar system did not produce any phase transition of H 2 O ice from amorphous to crystalline forms in cometary size bodies located in the primitive Edgeworth-Kuiper Belt.
Mid-infrared 7–20μm imaging of Jupiter from ESO’s Very Large Telescope (VLT/VISIR) demonstrate th... more Mid-infrared 7–20μm imaging of Jupiter from ESO’s Very Large Telescope (VLT/VISIR) demonstrate that the increased albedo of Jupiter’s South Equatorial Belt (SEB) during the ‘fade’ (whitening) event of 2009–2010 was correlated with changes to atmospheric temperature and aerosol opacity. The opacity of the tropospheric condensation cloud deck at pressures less than 800mbar increased by 80% between May 2008 and July
This report is the follow-up of the paper of A. Drouart et al. (1999, Icarus 140, 129) in which i... more This report is the follow-up of the paper of A. Drouart et al. (1999, Icarus 140, 129) in which it was demonstrated that appropriate models of the solar nebula permit us to interpret the deuterium enrichment in water with respect to the protosolar D/H ratio measured in LL3 meteorites and comets. In the present report, we show that the models selected by Drouart et al. are also able to explain D/H in HCN measured in Comet C/1995 O1 (Hale-Bopp). We find that the D/H ratio in HCN entering the nebula is ∼4 × 10 −3 , which is significantly less than values measured in cold dark clouds, but consistent with values found in hot molecular cores. Both H 2 O and HCN ices infalling from the presolar cloud onto the nebula discoid evaporated in the turbulent part of the nebula, isotopically exchanged with hydrogen, and mixed with water vapor coming from the inner part of the nebula. Subsequently, H 2 O and HCN ices with D/H ratios measured in Comet Hale-Bopp condensed, agglomerated and were incorporated in cometesimals. In the light of these results, we discuss the story of molecules detected in comets coming from Oort cloud. Most molecules detected in Comet Hale-Bopp originated from ices embedded in the presolar cloud. Ices vaporized prior to entering into the nebula or in the early nebula, and subsequently recondensed, except highly volatile molecules. According to A. Kouchi et al. (1994, Astron. Astrophys. 290, 1009), water ice condensed in crystalline form. We discuss the possibility that the most volatile species were then trapped in the form of clathrate hydrates. The oversolar C/N ratio and the strong depletion of Ne/O with respect to the solar abundance observed in comets are in agreement with the theory of clathrate hydrates of J. I. Lunine and D. J. . Comets formed in the Kuiper belt may contain amorphous water ice and have kept the isotopic signature of the presolar cloud. New published models of interiors of Uranus and Neptune permit us to calculate that the D/H ratios in proto-uranian and protoneptunian water ices are in agreement with those measured in comets. This confirms the current assumption that cometesimals and planetesimals that formed the cores of Uranus and Neptune had similar compositions.
Protoplanetary disks start their lives with a dust free inner region where the temperatures are h... more Protoplanetary disks start their lives with a dust free inner region where the temperatures are higher than the sublimation temperature of solids. As the star illuminates the innermost particles, which are immersed in gas at the sublimation edge, these particles are subject to a photophoretic force. We examine the motion of dust particles at the inner edge of protoplanetary disks
We study the formation conditions of icy planetesimals in protoplanetary disks in order to determ... more We study the formation conditions of icy planetesimals in protoplanetary disks in order to determine the composition of ices in small and cold extrasolar planets. Assuming that ices are formed from hydrates, clathrates, and pure condensates, we calculate their mass fractions with respect to the total quantity of ices included in planetesimals, for a grid of disk models. We find that the composition of ices weakly depends on the adopted disk thermodynamic conditions, and is rather influenced by the initial composition of the gas phase. The use of a plausible range of molecular abundance ratios and the variation of the relative elemental carbon over oxygen ratio in the gas phase of protoplanetary disks allow us to apply our model to a wide range of planetary systems. Our results can thus be used to constrain the icy/volatile phase composition of cold planets evidenced by microlensing surveys, hypothetical ocean planets, and carbon planets, which could be detected by COROT or Kepler. Subject headingg s: planetary systems -planetary systems: formation
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Papers by O. Mousis