P. Bruston

Interuniversity Laboratory of Atmospheric Systems, Lutetia Parisorum, Île-de-France, France

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Publications (47)115.31 Total impact

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    ABSTRACT: The study of the minor constituents of the planetary atmospheres from the analysis of the scattered light properties requires the knowledge of the absolute incident solar irradiance at high resolution. The data were obtained from the UVSP experiment on board the Solar Maximum Mission satellite in the 184.5–232.5nm spectral range. We have reconstituted the solar spectrum measured in three different regions of the solar disk with a spectral resolution of 0.01nm and a spatial resolution of 3arcsec. The wavelength scale was determined with a standard deviation of 0.0025nm. The comparison of the relative intensities in three locations of the solar disk with those obtained by other authors allowed us to determine these positions accurately and to derive the integrated spectrum of the whole disk. Finally, the resulting spectrum has been expressed in absolute units using the spectral irradiance by the SOLSPEC and SUSIM spectrometers, respectively operated with the ATLAS 1 mission and from the Upper Atmosphere Research Satellite. We obtained the absolute solar irradiance with an accuracy of 10% in the 184.5–232.5nm spectral range with a spectral resolution of 0.01nm for the first time using data from space observations.
    Solar Physics 06/2001; 201(2):253-269. · 3.26 Impact Factor
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    ABSTRACT: Laboratory spectral data (peak positions and integrated band intensities) of the infrared bands of acrylonitrile (CH2CHCN) gas in the region 4000-220 cm-1 are presented. Even though CH2CHCN has not yet been identified in Titan's atmosphere, it is among the possible photochemical and cosmic irradiation products of CH4 + N2 chemistry in the atmosphere of Titan. Laboratory simulations of Titan's atmospheric chemistry also give CH2CHCN as a product species. The results of our evaluation of the infrared intensity data provide an upper limit of the stratospheric abundance of CH2CHCN. Copyright 1999 Academic Press.
    Journal of Molecular Spectroscopy 05/1999; 194(2):206-210. · 1.67 Impact Factor
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    ABSTRACT: Titan, the largest satellite of Saturn, with a dense atmosphere very rich in organics, and many couplings in the various parts of its "geofluid", is a reference for studying prebiotic chemistry on a planetary scale. New data have been obtained from experiments simulating this organic chemistry (gas and aerosol phases), within the right ranges of temperature and a careful avoiding of any chemical contamination. They show a very good agreement with the observational data, demonstrating for the first time the formation of all the organic species already detected in Titan atmosphere including, at last, C4N2, together with many other species not yet detected in Titan. This strongly suggests the presence of more complex organics in Titan's atmosphere and surface, including high molecular weight polyynes and cyanopolyynes. The NASA-ESA Cassini-Huygens mission has been successfully launched in October 1997. The Cassini spacecraft will reach the Saturn system in 2004 and become an orbiter around Saturn, while the Huygens probe will penetrate into Titan's atmosphere. In situ measurements, in particular from Huygens GC-MS and ACP instruments, will provide a detailed analysis of the organics present in the air, aerosols, and surface. This very ambitious mission should yield much information of crucial importance for our knowledge of the complexity of Titan's chemistry, and, more generally for the field of exobiology.
    Advances in Space Research 02/1999; 24(4):453-60. · 1.18 Impact Factor
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    ABSTRACT: The Chemical Analysis of Released Gas Experiment (CHARGE), is one of several investigations selected for the Champollion New Millennium DS4 Mission. CHARGE is presently being designed to carry out a detailed molecular and isotopic analysis of material collected for the surface and several centimeters below the surface of comet Tempel I. The highest priority scientific issues addressed by this investigation include: the chemical conditions present in the region of cometary formation; the chemical changes during cometary formation and over the lifetime of the comet; the relationship of comets to other primitive and more evolved bodies in the solar system and to the parent interstellar cloud; the contribution of cometary material to the atmospheres and oceans of planets; and the nature of the mixture of ices and dust grains which give rise to the coma and extended sources of gas as a comet approaches perihelion. CHARGE will be designed to thermally process samples of solid phase material from near the ambient temperature to approximately 900 K. Gases evolved from the frozen ices will be continuously analyzed as a function of sample temperature by a quadrupole mass spectrometer with a mass range of 2 to 300 amu. A broad range of major and trace species, both organic and inorganic, from the gases evolved from the solid samples will undergo both chemical and cold trapping for subsequent analysis by gas chromatograph mass spectrometer (GCMS) analysis. CHARGE technology heritage includes the Galileo Probe Mass Spectrometer (Niemann et al., 1996) that successfully measured the composition of Jupiter's atmosphere in December of 1995. The landed portion of the mission will enable analysis of subsurface materials and allow identification of organic species present at sub-parts per million mole-fraction in the nucleus. Prior to the landed operations, CHARGE will carry out measurements from orbit for a period of several weeks.
    Advances in Space Research. 01/1999;
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    L. Guez, C. P. McKay, P. Bruston, F. Raulin
    01/1999; 31:1136.
  • L. Guez, C. P. McKay, P. Bruston, F. Raulin
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    ABSTRACT: We have added a model of methane condensation into a radiative equilibrium model of the temperature profile of Titan's atmosphere. We have assumed that particles settling from the upper atmosphere serve as condensation nuclei for methane, and that nucleation of methane occurs readily on every such particle. We have used a tropospheric eddy diffusion of 0.2 m2.s-1, as a nominal value. In that case, the flux of condensation nuclei is high enough and the eddy diffusion coefficient is low enough that supersaturation is negligible. Methane condensation then has a significant effect on the temperature profile. The effect is twofold: through opacity and through latent heat. Substituting cloud opacity to haze opacity in the condensation region leads to an increase of about 1.5 K for the surface temperature. The absorption of latent heat associated to evaporation a few kilometers above the surface brings back the surface temperature about 2 K down. Besides, the release of latent heat accompanying condensation increases the temperature in the middle troposphere, by as much as 5 K at 20 km. All those values vary in the same direction as the eddy diffusion coefficient. The temperature increase in the middle troposphere improves the fit to the profile derived from Voyager radio-occultation data. However, the modeled surface temperature is too low. Limited methane nucleation and condensation, leading to methane supersaturation, may increase the surface temperature while still releasing significant latent heat in the middle troposphere. Alternatively, methane supersaturation could be due to a high eddy diffusion coefficient. Modeling the impact of latent heat release will allow to discriminate between those two possibilities.
    09/1998;
  • N. S. Smith, Y. Bénilan, P. Bruston
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    ABSTRACT: We have measured the mid UV (195–265 nm) absorption coefficients of diacetylene, C4H2, over the temperature range 193–293 K. An impurity involved in the synthesis of C4H2, namely C4H3Cl, can strongly influence the measured absorption coefficients. This impurity has a mid UV absorption approximately 300 times stronger than C4H2 and we demonstrate that its presence, at low levels, in previously published spectra has strongly influenced the published coefficients and their temperature dependence. We have obtained an ultra-pure sample of C4H2 by repeated distillation and show here its clean spectrum and temperature dependence. We confirm previous band assignments, but our superior resolution (0.02 nm) has shown the presence of other, previously undetected bands. These new results have wide implications for the modelling of Titans atmosphere and the analysis of observational data.
    Planetary and Space Science 01/1998; 46(9):1215-1220. · 2.11 Impact Factor
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    ABSTRACT: The largest satellite of Saturn, Titan, is the only one in the solar system having a dense atmosphere. In many aspects it is similar to the Earth. Moreover, organic chemistry on Titan and prebiotic chemistry on Earth involve the same N-containing organic molecules: nitriles, including acetylenic nitriles and dinitriles, and their oligomers. Thus, in spite of much lower temperatures and the absence of liquid water, because of its environment very rich in organics, and the many couplings involved in the various parts of its “geofluid”, Titan is a reference laboratory for studying prebiotic chemistry on a planetary scale. In the frame of the NASA-ESA Cassini-Huygens mission, which includes an orbiter (Cassini) around Saturn and a probe (Huygens) in Titan's atmosphere, organic chemistry in Titan's “geofluid” will be studied in great detail. In situ measurements, in particular from Huygens GC-MS and ACP instruments, will provide detailed analysis of the organics present in the air, aerosols, and surface. The mission will be launched in october 1997, for an arrival in the Saturn System in 2004. Thus, at horizon 2000, we can expect many information of crucial importance for the field of exobiology.
    Advances in Space Research. 01/1998;
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    L. Guez, P. Bruston, F. Raulin, C. Régnaut
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    ABSTRACT: The uncertainty about possible supersaturation of methane, condensation of volatile species and the existence of clouds in Titan's lower atmosphere affects our understanding of photochemistry, the nature of the surface and the atmospheric thermal structure. Indeed, photochemistry depends on the depth of penetration of energetic photons, affected by methane abundance. Radar and infrared observations of bright surface regions have been explained by rain washing of highlands. As for the thermal profile, it is sensitive to CH4N2 gas opacity, cloud opacity and could be influenced by latent heat exchange. A rudimentary model with no methane supersaturation and gas transport by eddy diffusion indicates a methane latent heat release of 0.2 W m−2 between 20 and 30 km altitude for a surface mole fraction of 4.4% and an eddy diffusion coefficient of 0.2 m2s−1. Description of nucleation seems to be one of the first improvements which should be included in a model of phase changes. The suspicion of difficult methane nucleation comes from analysis of Voyager IRIS spectra. Moreover, species are expected to condense to the solid phase, which excludes very efficient nucleation and condensation processes associated with the presence of a liquid phase, such as deliquescence. The classical theory of heterogeneous nucleation, despite its deficiencies, is employed in atmospheric models, owing to its general nature and relative simplicity. Yet, it requires physical quantities for which experimental values do not exist. It is shown how surface free enthalpies of solids and contact angles may be linked to other material properties which are within reach of laboratory experiments, mainly ultraviolet absorption spectra of solid phases. It is found that a value of 10−9–10−7 s−1 for the “critical nucleation rate” (per nucleus) is adapted to the case of Titan, though we question the ability of the critical rate concept to make predictions for the condensation altitudes. A possible consequence of difficult methane nucleation is periodic evolution of the lower atmosphere, on a timescale of the order of 102 years.
    Planetary and Space Science 06/1997; · 2.11 Impact Factor
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    ABSTRACT: Laboratory experiments simulating organic synthesis in Neptune's atmosphere have been performed. We have submitted to a spark discharge gaseous mixtures containing 9 mbar of molecular nitrogen and 3 mbar of methane (the p(N2)/p(CH4) ratio is compatible with upper limits in Neptune's stratosphere) with varying quantities of molecular hydrogen. The spark discharge is used to model the energetic electrons produced by the impact of cosmic rays on the high atmosphere of Neptune. HCN is synthesized in the described experimental conditions, even with a low mixing ratio of molecular nitrogen. Studying the variation of HCN production with the initial composition of the gas mixture and extrapolating to high mixing ratio of molecular hydrogen allows to estimate HCN production in Neptune's atmosphere. The computed HCN production flux is 7x10(7) m-2 s-1, which is two orders of magnitude lower than the value predicted by chemical models for an internal source of N atoms. The major uncertainty in our extrapolation is the energetic distribution of electrons, implicitly assumed comparable in the discharge and in Neptune's atmosphere. We note that this distribution is also a source of uncertainty in chemical models. The chemical mechanism responsible for the local formation of HCN in the stratosphere probably occurs in the reactor too. We propose a simple characterization of the spark discharge. We thus link the molecular nitrogen dissociation cross section by electron impact to the measured parameters of the experiments (current, voltage, initial partial pressures) and to the resulting HCN partial pressures. However, other laboratory experiments with larger hydrogen pressures, requiring a more powerful electric source, have to be performed to yield a value of the cross section.
    Advances in Space Research 02/1997; 19(7):1135-44. · 1.18 Impact Factor
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    ABSTRACT: The IR spectrum of gaseous dicyanoacetylene, NCCCCN, is studied in the 3500-220 cm−1 range, employing Fourier transform spectroscopy. A total of 17 bands are analyzed and assigned. The absolute intensity is determined and the associated uncertainty is estimated for each of the bands. The resulting data are used to study the detectability of gaseous C4N2 in Titan's atmosphere. In particular a better estimate of the upper limits of its abundance in Titan's atmosphere is obtained when our results are used to reanalyse Voyager IRIS infrared spectra.
    Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy - SPECTROCHIM ACTA PT A-MOL BIO. 01/1997; 53(5):707-712.
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    ABSTRACT: In the frame of a program of systematic studies to determine or reassess the absolute intensities of gas phase organics of interest to Titan, we have experimentally studied the IR spectra in the gas phase of diazomethane, methyl azide, and methyl isocyanide, at room temperature, in the 250–4300 cm−1region. The absolute intensities,Sν, of the most intense vibrational bands of these compounds were determined experimentally together with the associated uncertainties. In order to estimate the detectability of the selected compounds by infrared spectroscopy in Titan's atmosphere, our data were compared with Voyager IRIS spectra of Titan. Upper limits of, respectively, 5, 5.4, and 1.3 ppb on the mean stratospheric abundances are inferred. These values are consistent with photochemical modeling of Titan's atmosphere. They appear auspicious for possible detection in Titan using upcoming space missions.
    Icarus 11/1996; 124(1):318–328. · 3.16 Impact Factor
  • Origins of Life and Evolution of Biospheres 09/1996; 26(3):531-531. · 1.83 Impact Factor
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    ABSTRACT: Three organic compounds (HC3N, C6H2, and C4N2) relevant of Titan's atmosphere have been studied within the framework of the SIPAT (Spectroscopie UV d'Intrt Prbiologique dans l'Atmosphre de Titan) program. Since this facility is still unable to reach the very low temperatures (170 K) of Titan's high atmosphere, spectra have to be obtained at several absorption-cell temperatures, and the data extrapolated towards lower temperatures. Previously published HC3N and C6H2 absorption coefficient data are reviewed, while new spectroscopic data are presented on C4N2. Integrated intensity calculations over the vibrational bands are performed apart from the background continuum. Thus, only the band contrast is considered here. While, the temperature dependence of the hot-band integrated intensity follows a Boltzmann distribution, we have enhanced the fit through an empirical parametrisation to account for the observed temperature dependence of the C4N2 and HC3N absorption coefficients, and to extrapolate those data to the low temperature conditions of Titan's high atmosphere. Finally, we discuss the implications of the results to possible detection by remote sensing observations of these minor compounds in Titan's atmosphere.
    Astrophysics and Space Science 01/1996; 236(1):85-95. · 2.06 Impact Factor
  • F Raulin, P Bruston
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    ABSTRACT: UV induced syntheses of organic compounds from the main atmospheric constituents can be a very important source of organics in a given planetary environment provided the atmosphere is in a reduced state. The evolution of a CO2 rich medium only produces very low yields of formaldehyde and related oxygenated compounds. Considering a CO rich atmosphere, the photochemical yield of O-organics formation is much higher, when the synthesis of N-organics remains difficult. The most favourable atmosphere as far as photochemical organic synthesis is concerned is a CH4 rich milieu.. The photochemical evolution of such a CH4 atmosphere under UV irradiation leads to a chain of various organics, the complexity of which increases together with the number of pathways involved in their formation. Their complexity also closely correlates with their UV photoabsorption spectrum: the more complex they are, the more shifted is their UV spectrum toward the visible range. Direct photodissociation of methane requires UV photon of wavelengths shorter than about 145 nm. It mainly produces ethane which absorbs UV at wavelengths shorter than about 160 nm, and acetylene, that presents an absorption spectrum extending up to 200 nm. This shift still continuously increases with further increase in number of C atoms. Unsaturated hydrocarbons with 4 and more C atoms have UV absorption characteristics including noticeable band structures in the 250–300 nm range. This trend has very important implication in the photochemical behaviour of a CH4-rich planetary atmosphere, as it induces many catalytic processes. The occurrence of such processes is closely related to vertical atmospheric and energy deposition profiles. Titan provides a very good example of such a UV-directed organic atmospheric chemistry.
    Advances in Space Research 01/1996; · 1.18 Impact Factor
  • 05/1995; 27:1096.
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    ABSTRACT: Organic chemistry on Titan and prebiotic chemistry on Earth involve the same N-containing organics: nitriles and their oligomers. Couplings of their chemistry in the three parts of Titan's geofluid (atmosphere, aerosols and surface) seem to play a key role in the organic chemical evolution of the planet. If liquid water was present on Titan, then a prebiotic chemistry, involving eutectics, similar to that of the early Earth, may have occurred. However, liquid water is currently absent and a prebiotic chemistry based only on N-organics may be evolving now on Titan. The other consequence of the low temperatures of Titan is the possible formation of organics unstable at room temperature and very reactive. So far, these compounds have not been systematically searched for in experimental studies of Titan's organic chemistry. C4N2 has already been detected on Titan. Powerful reactants in organic chemistry, CH2N2, and CH3N3, may be also present. They exhibit spectral signatures in the mid-IR strong enough to allow their detection at the 10-100 ppb level. They may be detectable on future IR spectra (ISO and Cassini) of Titan.
    Advances in Space Research 04/1995; 15(3):321-33. · 1.18 Impact Factor
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    ABSTRACT: With a dense N2-CH4 atmosphere rich in organics, both in gas and aerosol phases, and with the possible presence of hydrocarbons oceans on its surface, Titan, the largest satellite of Saturn, appears as a natural laboratory to study chemical evolution toward complex organic systems, in a planetary environment and over a long time scale. Thanks to many analogies with planet Earth, it provides a unique way to look at the various physical and chemical processes, and their couplings which may have been involved in terrestrial prebiotic chemistry. Indeed, analogies with the Earth have a limit since Titan's temperatures are much lower than on the Earth and since liquid water is totally absent. However, from that aspect, Titan also serves as a reference laboratory worth studying — indirectly — the role of liquid water in exobiology. The Cassini-Huygens mission currently developed by NASA and ESA will send an orbiter around Saturn and Titan and a probe in Titan's atmosphere. This mission which will be launched in 1997 for an expected arrival in 2004, offers a unique opportunity to study in detail extra-terrestrial, not life-controled, organic processes, and consequently it will have significant implications in the fields of exobiology and the origins of life.
    Journal of Biological Physics 01/1995; 20(1):39-53. · 0.95 Impact Factor
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    ABSTRACT: We have reviewed the most recent results on acetylene absorption in the weak A-X band system (features longward of 185 nm). Then, using acetone absorption measurements in the 185–200 nm range together with saturated vapor pressure studies of acetone, we are able to resolve discrepancies noted by several authors for some A-X bands.
    Geophysical Research Letters - GEOPHYS RES LETT. 01/1995; 22(8):897-900.
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    ABSTRACT: The interpretation of mid-UV albedo spectra of planetary atmospheres, especially that of Titan, is the main goal of the SIPAT (Spectroscopie uv d'Interet Prebiologique dans l'Atmosphere de Titan) research program. This laboratory experiment has been developed in order to systematically determine the absorption coefficients of molecular compounds which are potential absorbers of scattered sunlight in planetary atmospheres, with high spectral resolution, and at various temperatures below room temperature. From photochemical modelling and experimental simulations, we may expect triacetylene (C6H2) to be present in the atmosphere of Titan, even though it has not yet been detected. We present here the first determination of the absolute absorption coefficient of that compound in the 200-300 nm range and at two temperatures (296 K and 233 K). The temperature dependence of the C6H2 absorption coefficient in that wavelength range is compared to that previously observed in the case of cyanoacetylene (HC3N). We then discuss the implications of the present results for the interpretation of Titan UV spectra, where it appears that large uncertainities can be introduced either by the presence of trace impurities in laboratory samples or by the variations of absorption coefficients with temperature.
    Planetary and Space Science 01/1995; 43(1-2):83-9. · 2.11 Impact Factor

Publication Stats

324 Citations
115.31 Total Impact Points

Institutions

  • 1994–2001
    • Interuniversity Laboratory of Atmospheric Systems
      Lutetia Parisorum, Île-de-France, France
  • 1996
    • Université Paris-Sud 11
      • Laboratoire de Photophysique Moléculaire
      Paris, Ile-de-France, France
  • 1994–1996
    • Université Paris-Est Créteil Val de Marne - Université Paris 12
      • Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA) - UMR CNRS 7583
      Créteil, Île-de-France, France
  • 1995
    • French National Centre for Scientific Research
      • Laboratoire inter-universitaire des systèmes atmosphèriques (LISA)
      Paris, Ile-de-France, France
  • 1988–1991
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
    • Institut d'Astrophysique Spatiale
      Lutetia Parisorum, Île-de-France, France