In situ measurements of the physical characteristics of Titan’s environment. Nature

LESIA, Observatoire de Paris, 5 Place Janssen, 92195 Meudon, France. [2
Nature (Impact Factor: 41.46). 01/2006; 438(7069):785-91. DOI: 10.1038/nature04314
Source: PubMed

ABSTRACT On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was mainly nitrogen, with some methane, but its temperature and pressure profiles were poorly constrained because of uncertainties in the detailed composition. The extent of atmospheric electricity ('lightning') was also hitherto unknown. Here we report the temperature and density profiles, as determined by the Huygens Atmospheric Structure Instrument (HASI), from an altitude of 1,400 km down to the surface. In the upper part of the atmosphere, the temperature and density were both higher than expected. There is a lower ionospheric layer between 140 km and 40 km, with electrical conductivity peaking near 60 km. We may also have seen the signature of lightning. At the surface, the temperature was 93.65 +/- 0.25 K, and the pressure was 1,467 +/- 1 hPa.

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Available from: R. Grard, Sep 29, 2015
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    • "As evident from the change of the infrared spectra with increasing temperature , the C 4 N 2 pure amorphous ice crystallizes around 95 K. This temperature is close to Titan's surface temperature of 94 K (Fulchignoni et al., 2005). Hence under the present experimental conditions at 100 K, C 4 N 2 condensed films are crystalline. "
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    ABSTRACT: Following our recent communication (Gudipati, M.S. et al. [2013]. Nat. Commun. 4, 1648. on the discovery of condensed-phase non-volatile polymeric material with similar spectral features as tholins, we present here a comprehensive spectroscopic study of photochemical formation of polymeric material from condensed dicyanoacetylene (C4N2) ice films. C4N2 is chosen as starting material for the laboratory simulations because of the detection of this and similar molecules (nitriles and cyanoacetylenes) in Titan’s atmosphere. UV–Vis and infrared spectra obtained during long-wavelength (>300 nm) photon irradiation and subsequent warming of the ice films are used to analyze changes in C4N2 ice, evolution of tholins, and derive photopolymerization mechanisms. Our data analysis revealed that many processes occur during the photolysis of condensed Titan’s aerosol analogs, including isomerization and polymerization leading to the formation of long-chain as well as aromatic cyclic polymer molecules. In the light of tremendous new data from the Cassini mission on the seasonal variations in Titan’s atmosphere, our laboratory study and its results provide fresh insight into the formation and evolution of aerosols and haze in Titan’s atmosphere.
    Icarus 05/2014; 234:81–90. DOI:10.1016/j.icarus.2014.02.016 · 3.04 Impact Factor
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    • "This in turn affects the rate of photoemission of electrons in the atmosphere. Fulchignoni et al. (2005) and Hamelin et al. (2007) reported the electrical measurements made using the PWA subsystem, which is a component of the Huygens Atmospheric Structure Instrument (HASI) during the Huygens probe landing at Titan . PWA detected an ionized layer in the altitude region of 50–80 km, attributed mainly to GCRs, with a maximum conductivity at around 60–65 km, although the previous models (Molina-Cuberos et al., 1999; Borucki et al., 1987, 2006) predicted instead a peak at higher altitude, at around 90–100 km. "
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    ABSTRACT: The atmospheric electrical conductivity measured by the Permittivity, Wave and Altimetry (PWA) subsystem on board the Huygens Probe, during the landing mission on Titan, has been modeled in the present work. Previous modeling studies showed a Galactic Cosmic Ray (GCR) peak of conductivity at a higher altitude and a quantitative overestimation in the altitude range 0-100 km compared to that observed by the PWA instrument. Recently the PWA data was revisited and provided new constraints on the conductivity at altitudes 100 - 180 km. Because the aerosols in the atmosphere are known to alter the electron concentration, using a detailed distribution of the aerosols at all altitudes, the electron conductivity has been calculated in the altitude range 0-180 km. By using a variable range of photoemission threshold for the aerosols, the present model is able to reasonably predict the altitude at which the GCR peak of conductivity occurs and to meet the new constraints for the conductivity profile.
    Icarus 05/2014; 238. DOI:10.1016/j.icarus.2014.04.018 · 3.04 Impact Factor
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    • "Precise knowledge of methane absorption is crucial in the study of planetary systems because its spectral features are used to determine the physical properties of these atmospheres [1] [2] [3]. This is especially true for Titan (Saturn's largest satellite) whose atmosphere is composed of 98.6% nitrogen and 1.4% methane at temperatures ranging between 70 K and 200 K. Improving the methane spectroscopic parameters is essential [4] [5] [6] for full interpretation of near infrared observations returned by the ground-based and orbiting observatories. "
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    ABSTRACT: A new study of 12CH4 line positions and intensities was performed for the lower portion of the Tetradecad region between 4800 and 5300 cm−1 using long path (1603 m) spectra of normal sample CH4 at three pressures recorded with the Fourier transform spectrometer in Reims, France. Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective Dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. An existing spectrum of enriched 13CH4 was used to discern the isotopic lines. A new measured linelist produced positions and intensities for 5851 features (a factor of two more than prior work). Assignments were made for 46% of these; 2725 experimental line positions and 1764 selected line intensities were fitted with RMS standard deviations of 0.004 cm−1 and 7.3%, respectively. The RMS of prior intensity fits of the lower Tetradecad was previously a factor of two worse. The sum of observed intensities between 4800 and 5300 cm−1 fell within 5% of the predicted value from variational calculations.
    Journal of Quantitative Spectroscopy and Radiative Transfer 05/2014; 138. DOI:10.1016/j.jqsrt.2014.02.005 · 2.65 Impact Factor
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