Indications of supersaturated stratospheric methane in Neptune from its atmospheric thermal profile

An iterative inversion method is used to retrieve the thermal structure of Neptune from available infrared measurements. The most plausible thermal profile leads to an effective temperature of 58.4°K, implying the presence of an internal heat source equal to about 1.6 times the solar-absorbed power. The interpretation of Neptunian infrared measurements in the 8-μm range requires a very strong supersaturation of CH₄ in the upper atmosphere of the planet.     

Scattering from a fractal surface: acoustical experiments and comparison with near-nadir models

A homogeneous resin print of the surface of a naturally-fractured granite block with an experimental Hurst exponent H?0.7 is placed in a water tank. An acoustical source insonifies the surface in a near-nadir direction and the backscattered waves are recorded near the source. Such measurements are made at different positions along a profile above the surface in order to obtain the energy spectrum of the mean backscattered wavefield. The wavelength range considered is 0.58?λ?8.72 mm in water. A synthetic energy spectrum is obtained from a model [Shepard and Campbell, Icarus 141 (1999) 156] which represents the rough surface as an ensemble of point scatterers and assumes a single-scattering regime. This model reasonably fits with the experimental spectrum with the largest discrepancies observed for λ<2.5 mm. The fit is improved in the whole wavelength interval by accounting for the long-range topography variations occurring along the averaging profile.     

Airborne interferometric measurement of the infrared spectrum of Jupiter from 6 to 14 μm

A new spectrum of Jupiter from 700 to 1600 cm^?1 was obtained with an interferometric experiment using the 91.5 cm telescope of the NASA Airborne Infrared Observatory. The spectral resolution is 10 cm^?1 and the signal-to-noise ratio is 30 at 900 cm^?1. NH₃ absorption lines are observed between 820 and 1020 cm^?1. The 1306 cm^?1ν₄CH₄ band strongly appears in emission at a temperature of at least 145° K. The Jovian brightness temperature between 1400 and 1600 cm^?1, according to our measurement, is lower than 170° K.     

On the detectability of H2S in Jupiter

The influence of hydrogen sulfide, a still-undetected key molecule for the Jovian atmospheric chemistry in the infrared spectrum, was investigated. Synthetic spectra including various vertical distribution profiles of H₂S have been computed and compared with observational data for Jupiter in the 2- to 15-cm^?1 and 1160- to 1200-cm^?1 spectral ranges. No firm conclusion about the presence of H₂S can be drawn from the latter spectral region because of large uncertainties in gaseous opacities. In the microwave range, H₂S is found to be a possible candidate to explain the measurements. Constraints to its vertical distribution which would imply a significant supersaturation in the troposphere are derived. Physical and chemical processes involving H₂S in the atmosphere are discussed in the light of this hypothesis.     

A methodological approach of fluvial dynamics oriented towards hydrosystem management: case study of the Loire and Allier rivers

Abstract

This study was conducted as part of the European LIFE Loire Nature program for the conservation and management of a 110-km-long section of the Loire and Allier rivers, an area renowned for its ecological richness. The methodological approach is based on statistical analysis (bivariate and multivariate analyses) of hydro-geomorphologic and biogeographical variables, complemented by reach typology and mapping. The main results show, on the one hand, the great spatial variability of fluvial mosaic complexity along the river continuum and on the other hand, some independence between the riparian forest characteristics and the channel forms. The fluvial pattern (e.g. anabranching) and the forest establishment along the Loire river register specific features. © 2000 Éditions scientifiques et médicales Elsevier SAS     

Infrared spectra of gaseous mononitriles: Application to the atmosphere of Titan

A list of volatile nitriles, not yet detected in the atmosphere of Titan, but likely to be present in this environment, has been selected: acetonitrile, propionitrile, acrylonitrile, crotononitrile, allyl cyanide, methacrylonitrile, and cyanopropyne. The spectra of these compounds in the gas phase have been systematically studied, in the mid- and far-infrared ranges. For each selected nitrile, the most intense vibration bands have been determined. Their strengths have been characterized by estimating the monochromatic absorption coefficient at the maximum(s) of the bands, and the integrated absorbance over the entire band. Then, in order to estimate the detectability of the selected compounds by infrared spectroscopy in the atmosphere of Titan, the data obtained have been extrapolated to the case of Titan.     

New Constraints on the Composition of Jupiter from Galileo Measurements and Interior Models

Using the helium abundance measured by Galileo in the atmosphere of Jupiter and interior models reproducing the observed external gravitational field, we derive new constraints on the composition and structure of the planet. We conclude that, except for helium which must be more abundant in the metallic interior than in the molecular envelope, Jupiter could be homogeneous (no core) or could have a central dense core up to 12M_⊕. The mass fraction of heavy elements is less than 7.5 times the solar value in the metallic envelope and between 1 and 7.2 times solar in the molecular envelope. The total amount of elements other than hydrogen and helium in the planet is between 11 and 45M_⊕.     

Shale-Gas Assessment: Comparison of Gas-In-Place Versus Performance-Based Approaches

The recent interest in exploration for shale gas increases the demand for a reliable, compatible resource assessment. Many different assessment methods are used, commonly depending on types and quantity of data available, which may lead to significantly divergent results for the same shale-gas play. This study compares results obtained using performance-based and gas-in-place methodologies to assess a well-developed and active shale-gas play (Woodford Shale, Arkoma Basin, USA) and two untested, hypothetical shale-gas plays (Shublik and Brookian, Alaska North Slope, USA). Results show that the two assessment methods produce comparable results when assessment units are identically defined and similar geological constraints are used as input parameters. Inherent uncertainties are associated with both assessment methods, and these are related to aspects of shale-gas production that are not well understood. The performance-based method relies on decline trend analysis to generate distributions of estimated ultimate recovery (EUR), and uncertainty increases in cases of short production history. The gas-in-place method requires the application of a recovery factor to estimate technically recoverable resources, and both absolute values of recovery factors and their spatial variability are poorly documented, and therefore a source of uncertainty.     

Nitrile gas chemistry in Titan’s atmosphere

This work presents the first study of the gaseous products resulting from the partial dissociation of methane and nitrogen in the PAMPRE experimental setup simulating Titan’s atmospheric chemistry.Using cryogenic trapping, the gaseous products generated from the chemical reactions occurring in the reactor have been trapped. Analyses of these products by gas chromatography coupled to mass spectrometry have allowed the detection and identification of more than 30 reaction products. Most of them are identified as nitrile species, accompanied by aliphatic hydrocarbons and a few aromatics compounds. The observed species are in agreement with the data from the recent Cassini-Huygens mission as well as from other laboratory setups capable of dissociating nitrogen and methane. This work emphasizes the probable importance of nitrogen-bearing compounds in the chemistry taking place in Titan’s atmosphere.Furthermore, a quantification of mono-nitriles with saturated alkyl chains has been performed relatively to hydrogen cyanide and shows a power law dependence in their concentration. This dependence is consistent with the Cassini-INMS data and Titan’s photochemical models.An empirical relationship has been extracted from our experimental data: [C_xH_2x−1N] = 100x⁻⁵, where x is the number of carbon atoms in the nitrile molecule. This relationship can be directly used in order to foretell the concentration of heavier nitriles induced by chemistry in Titan’s atmosphere.