Th. Encrenaz

Observatoire de Paris, Lutetia Parisorum, Île-de-France, France

Are you Th. Encrenaz?

Claim your profile

Publications (150)208.08 Total impact

  • Th. Encrenaz, C. Sotin, D. McCleese, J. Head
    Planetary and Space Science 01/2007; 55(3):255-257. · 2.11 Impact Factor
  • T. Owen, Th. Encrenaz
    [Show abstract] [Hide abstract]
    ABSTRACT: The enrichment of heavy elements on Jupiter discovered by the Galileo Probe can be easily explained if these elements were brought to the forming planet by low temperature solar composition icy planetesimals. These planetesimals would contain all the heavy elements in solar proportions, subsequently enriching the envelope equally, as observed in volatiles ranging from Ar to S. This simple model correctly predicted the ratio of C/H found by Cassini-Huygens on Saturn. It also explains the values of C/H found in other giant planet atmospheres, and leads to the observed values of D/H. For each planet, the mass of material required - about 8-12 EM - is remarkably similar, and is consistent with the requirements of the accretion-collapse model of giant planet formation. If this model is correct, it implies that these low temperature icy planetesimals were by far the most abundant form of solid matter in the early solar nebula.
    01/2006;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To follow the stunning success of Cassini-Huygens we propose a new mission to Saturn that will return the same fundamental information about this giant planet that we are already obtaining about Jupiter This will put us in a powerful position to refine models for the solar nebula and the origin and evolution of giant planets The Galileo Probe has given us the abundances and isotope ratios of krypton and xenon plus 5 of the 6 most abundant elements composing Jupiter The Juno Mission presently under development will provide the missing abundance of oxygen The Galileo data already show a surprising enrichment of heavy elements whose interpretation engenders new constraints on giant planet formation that may also change current models of the solar nebula Lacking comparable knowledge of Saturn's composition we cannot tell whether Jupiter is an anomaly or the norm Resolution of this issue obviously impacts our perspective on the formation of the newly discovered giant planets around other stars We can obtain the necessary information at relatively low cost by a multinational mission combining an atmospheric probe using Galileo and Cassini-Huygens inheritance with the microwave sounding capability developed for Juno One potential pairing would have ESA build the probe with a NASA heat shield while NASA builds the carrier with communications star tracker microwave antennas etc supplied by some combination of ASI and the space programs of other countries We will illustrate possible results of the mission
    01/2006; -1:605.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The OMEGA experiment onboard the Mars Express satellite provides spectral maps of Mars in the range from UV to near infrared The 2 56 micron band of atmospheric water vapour was used to retrieve its abundance and to study spatial and vertical distribution of the gas This particular study focuses on the water vapour behaviour in the vicinity of the Martian volcanoes The earlier findings by the ISM Phobos experiment indicated anomalous increase of the mixing ratio on the slopes of Tharsis volcanoes The OMEGA measurements confirm these results that imply virtually constant column density of atmospheric water above the volcanoes and around them Early morning observations also showed that water vapour peaks on the south-east flank close to the summit This behaviour excludes uniform mixing of the gas within the atmosphere but rather favors the suggestion that the atmospheric water is confined to a shallow layer near the surface and its content is mainly controlled by the regolith
    01/2006;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The OMEGA mapping spectrometer onboard Mars Express combines high spatial resolution (˜ 300 m/px at periapsis) and high S/N ratio (> 100 over the whole spectral range). The experiment is well-suited to study in detail the behavior of water vapor in specific regions. Here we focus our study on the Tharsis region and particularly on the four great volcanoes, which are known to be the sites of peculiar phenomena related to atmospheric water such as frequent cloud formation or vapor enrichment implied by the ISM/Phobos 2 observations. In our analysis we use the 2.56 micron band, which is the most sensitive and 3 - 5 times stronger than the other water bands in the OMEGA spectral range, and is expected to be free of mineralogical features. Our retrievals cover different seasons and local times, allowing us to study seasonal and diurnal variability of atmospheric water vapor. The water mixing ratio below the saturation level retrieved from the OMEGA data on the volcanoes is systematically higher than that above the surrounding terrain by a factor of ˜ 10. Corresponding column density ranges from 1 to 10 precipitable microns and strongly depends on the height of saturation level which changes from < 1 km to 10 km over the surface depending on season and local time. This behavior depicts a rather complex picture. The atmosphere over the volcanoes seems to be able to retain higher abundances of water vapor compared to the surrounding region, but the overall effect on column density is limited by condensation effects. The enhancement of water mixing ratio above the volcanoes can be qualitatively explained by the combination of transport by upslope winds and adsorption / desorption of water molecules by regolith on the volcanoes.
    01/2006;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: High-resolution infrared imaging spectroscopy of Mars has been achieved at the NASA Infrared Telescope Facility (IRTF) on June 19–21, 2003, using the Texas Echelon Cross Echelle Spectrograph (TEXES). The areocentric longitude was 206°. Following the detection and mapping of hydrogen peroxide H2O2 [Encrenaz et al., 2004. Icarus 170, 424–429], we have derived, using the same data set, a map of the water vapor abundance. The results appear in good overall agreement with the TES results and with the predictions of the Global Circulation Model (GCM) developed at the Laboratory of Dynamical Meteorology (LMD), with a maximum abundance of water vapor of 3±1.5×10−4(17±9 pr-μm). We have searched for CH4 over the martian disk, but were unable to detect it. Our upper limits are consistent with earlier reports on the methane abundance on Mars. Finally, we have obtained new measurements of CO2 isotopic ratios in Mars. As compared to the terrestrial values, these values are: (18O/17O)[M/E] = 1.03 ± 0.09; (13C/12C)[M/E] = 1.00 ± 0.11. In conclusion, in contrast with the analysis of Krasnopolsky et al. [1996. Icarus 124, 553–568], we conclude that the derived martian isotopic ratios do not show evidence for a departure from their terrestrial values.
    Icarus 12/2005; · 3.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: As solar-system bodies are cold objects, the low-frequency range, from the far-infrared to the millimetre, is very well suited for the study of planetary and cometary atmospheres, especially with heterodyne spectroscopy. Important results have been obtained in the past with ground-based antennas (detection of an atmosphere around Io, new species in Jupiter after Shoemaker-Levy 9 collision, about 20 parent molecules in comets). Herschel is expected to bring a major contribution to the study of water in the solar system (water cycle on Mars, oxygen external source in the giant planets, activity monitoring of comets, search for activity in distant objects, D/H in Kuiper-belt comets). Herschel will also accurately measure the D/H ratio in giant planets, a key parameter for understanding their formation processes. Both Herschel and ALMA will be used for searching for new minor species in planetary and cometary atmospheres, and for measuring the diameters of many trans-neptunian objects. Finally ALMA will be best suited for building 3-D dynamical pictures of planets, satellites and comets.
    01/2005;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Carbon monoxide has been detected for the first time in the atmosphere of Uranus, from infrared spectroscopy using ISAAC at the VLT. This result provides new constraints on the planet's interior, and illustrates significant differences between the two 'icy giants' Uranus and Neptune.
    The Messenger. 02/2004; 115:35-36.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Considering the possibility of outgassing from some localized sources on Mars, we have developed a one-dimensional photo-chemical model that includes methane (CH 4), sulfur dioxide (SO 2) and hydrogen sulfide (H 2 S). Halogens were considered but were found to have no significant impact on the martian atmospheric chemistry. We find that the introduction of methane into the martian atmosphere results in the formation of mainly formaldehyde (CH 2 O), methyl alcohol (CH 3 OH) and ethane (C 2 H 6), whereas the introduction of the sulfur species produces mainly sulfur monoxide (SO) and sulfuric acid (H 2 SO 4). Depending upon the flux of the outgassed molecules from possible hot spots, some of these species and the resulting new molecules may be detectable locally, either by remote sensing (e.g., with the Planetary Fourier Spectrometer on Mars Express) or in situ measurements.
    Advances in Space Research 01/2004; 33(12). · 1.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Hydrogen peroxide (H 2 O 2) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10 15 –10 16 cm −2 . However, a stringent upper limit of the H 2 O 2 abundance on Mars (9 × 10 14 cm −2) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. µm, Ls = 112 •). Here we report the detection of H 2 O 2 on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls = 206 •) when the global water vapor abundance was ∼ 10 pr. µm. The spatial distribution of H 2 O 2 shows a maximum in the morning around the sub-solar latitude. The mean H 2 O 2 column density (6 × 10 15 cm −2) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls = 254 •), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116–121).
    Icarus 01/2004; 170:424-429. · 3.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Spectroscopic remote sensing in the infrared and (sub)millimeter range is a powerful technique that is well suited for detecting minor species in planetary atmospheres (Planet Space Sci. 43(1995) 1485). Yet, only a handful of molecules in the Mars atmosphere (CO2, CO and H2O along with their isotopic species, O3, and more recently H2O2 and CH4) have been detected so far by this method. New high performance spectroscopic instruments will become available in the future in the infrared and (sub)millimeter range, for observations from the ground (infrared spectrometers on 8 m class telescopes, large millimeter and submillimeter interferometers) and from space, in particular the Planetary Fourier Spectrometer (PFS) aboard Mars Express (MEx), and the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory (HSO). In this paper we will present results of a study that determines detectability of minor species in the atmosphere of Mars, taking into account the expected performance of the above spectroscopic instruments. In the near future, a new determination of the D/H value is expected with the PFS, especially during times of maximum H2O abundance in the martian atmosphere. PFS is also expected to place constraints on the abundance of several minor species (H2O2,CH4,CH2O, SO2, H2S, OCS, HCl) above any local outgassing sources, the hot spots. It will be possible to obtain complementary information on some minor species (O3,H2O2, CH4) from ground-based infrared spectrometers on large telescopes. In the more distant future, HIFI will be ideally suited for measuring the isotopic ratios with unprecedented accuracy. Moreover, it should be able to observe O2, which has not yet been detected spectroscopically in the IR/submm range, as well as H2O2. HIFI should also provide upper limits for several species that have not yet been detected (HCl, NH3, PH3) in the atmosphere of Mars. Some species (SO, SO2,H2S, OCS, CH2O) that may be observable from the ground could be searched for with present single-dish antennae and arrays, and in the future with the Atacama Large Millimeter Array (ALMA) submillimeter interferometer.
    Planetary and Space Science 01/2004; · 2.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Several observational programmes were conducted with ISO (Kessler et al., 1996) aiming at the investigation of the near- and far- infrared spectrum of the satellites of the giant planets. Thus, Jupiter's satellites Callisto, Io and Ganymede were explored mainly with the spectrometers, while the spectrum of Titan, Saturn's largest satellite, was investigated thoroughly by all the instruments. The analysis of the data has provided original and precious information on the satellites' surfaces and Titan's atmosphere in particular.
    Advances in Space Research 11/2002; · 1.18 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have searched for H2O2 in the northern atmosphere of Mars, on Feb 2-3, 2001 (Ls = 112 deg.), at a time corresponding to maximum water vapor abundance in the northern hemisphere. The TEXES high-resolution grating spectrograph was used at the NASA/Infrared Telescope Facility (IRTF). Individual lines of the H2O2 nu 6 band have been searched for in the 1226-1235 cm-1 range (8.10-8.15 mu m). Data have been co-added for three different latitude sets: (1) full northern coverage (0-90 deg.); (2) low northern latitudes (10-40 deg.); (3) high northern latitudes (40-60 deg.). From the absence of detectable H2O2 lines in each of the three co-added data sets, we infer an H2O2 2-sigma upper limit of 7 1014 cm-2 in the first case, 2 1015 cm-2 in the second case, and 1015 cm-2 in the third case. These numbers correspond respectively to mean water vapor abundances of 30 pr-mu m, 20 pr-mu m and 40 pr-mu m at the time of our observations. Our lowest upper limit is ten times lower than the value derived by Krasnopolsky et al. (1997) in the southern hemisphere in June 1988 (Ls = 222 deg.); the mean water vapor abundance corresponding to their observation was 10 pr-mu m. Our lowest upper limit is about 10 times lower than the values predicted by global photochemical models, also calculated for a mean H2O abundance of 10 pr-mu m. However, taking into account the actual geometry of the observations and the corresponding conditions in the Martian atmosphere, the calculated H2O2 abundance becomes close to the observed upper limits by assuming an eddy diffusion coefficient of 107 cm2s-1 in the lower atmosphere of Mars.
    09/2002;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Although there is no evidence of active outgassing on Mars today, tantalizing clues to the possible existence of "localized" outgassing sources, the hotspots, may exist. A tentative detection of formaldehyde (CH2O) "locally" in the north equatorial region from the Phobos spacecraft in 1989 (1) and the indications of recent ground water seepage and surface runoff particularly at the middle and high latitudes(2) are two examples. Ground-based observations have failed to detect formaldehyde. Those observations were, however, "global", i.e. averaged over large areas, usually the disk or the hemisphere. Therefore, localized outgassing sources may not be ruled out. If the Phobos result is correct, the relatively short lifetime ( ~13 hrs) of CH2O would require a nearly continuous source of methane (CH4) in the detection region. Other than methane, sulfur species (H2S, SO2) are the likely principal outgassing species. Once in the atmosphere, these molecules and their photoproducts would react with the known martian molecules, producing new species. Starting with the current "global average" upper limits of CH4, SO2 and H2S of, respectively, 0.02, 0.1 and 0.1 ppm, and progressively increasing their abundances above possible hotspots, we calculate the abundances of the new molecules. We find that the introduction of methane into the martian atmosphere results in the formation of mainly formaldehyde, methyl alcohol (CH3OH) and ethane (C2H6), whereas the introduction of the sulfur species produces mainly SO and H2SO4. Depending upon the flux of the outgassed molecules from possible hotspots, some of these species and the resulting new molecules may be detectable locally-for example with the Planetary Fourier Spectrometer on Mars Express. (1) Korablev, et al., Planet. Space Sci., 41, 441, 1993. (2) Malin and Edgett, Science, 288, 2330, 2000.
    09/2002;
  • Th. Encrenaz
    [Show abstract] [Hide abstract]
    ABSTRACT: The Infrared Space Observatory (ISO) satellite, operated by ESA in 1995–1998, has provided a very significant contribution to our knowledge of planetary atmospheres. The main results of ISO observations of the giant planets and Titan can be summarized as follows: (1) a new determination of the D/H ratio; (2) the discovery of an external source of water, and the detection of CO2 in the stratospheres of Saturn, Neptune and Jupiter; (3) the detection of new hydrocarbons in the stratospheres of Saturn (CH3C2H, C4H2, C6H6, CH3), Jupiter (CH3C2H, C6H6) and Neptune (CH3, C2H4); (4) the study of NH3 and PH3 in Jupiter and Saturn, and the determination of 14N/15N in Jupiter; (5) the detection of H2O in the deep troposphere of Saturn; (6) the observation of H3+ in Uranus. ISO spectra of Mars have provided information about the water vapor content and the composition of aerosols.
    Advances in Space Research 01/2002; · 1.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Hydrogen peroxide H 2 O 2 has been suggested as a possible oxidizer of the Martian surface. However, this minor species has never been detected. Photochemical models suggest that H 2 O 2 and H 2 O abundances should be correlated. We have searched for H 2 O 2 in the northern atmosphere of Mars, on Feb. 2–3, 2001 (Ls = 112 deg), at a time corresponding to maximum water vapor abundance in the northern hemisphere. The TEXES high-resolution grating spectrograph was used at the NASA/Infrared Telescope Facility (IRTF). Individual lines of the H 2 O 2 ν 6 band were searched for in the 1226–1235 cm −1 range (8.10–8.15 µm). Data were co-added for three different latitude sets: (1) full northern coverage (0–90 deg); (2) low northern latitudes (10–40 deg); (3) high northern latitudes (40–60 deg). From the absence of detectable H 2 O 2 lines in each of the three co-added data sets, we infer an H 2 O 2 2-σ upper limit of 9 × 10 14 cm −2 in the first case, 1.2 × 10 15 cm −2 in the second case, and 1.1 × 10 15 cm −2 in the third case. These numbers correspond to mean water vapor abundances of 30 pr-µm, 20 pr-µm and 40 pr-µm at the time of our observations. Our lowest upper limit is eight times lower than the value derived by Krasnopolsky et al. (1997) in the southern hemisphere in June 1988 (Ls = 222 deg); the mean water vapor abundance corresponding to their observation was 10 pr-µm. Our lowest upper limit is between 2.5 and 10 times lower than the values predicted by global photochemical models, also calculated for a mean H 2 O abundance of 10 pr-µm. In view of this, we have developed a new photochemical model which takes into account the actual geometry of the observations and the corresponding conditions of the water vapor abundance, dust and temperature in the Martian atmosphere, inferred from the MGS/TES data. Assuming an eddy diffusion coefficient of 10 7 cm 2 s −1 in the lower atmosphere, the calculated H 2 O 2 abundance is only a factor 1.5 greater than the observed upper limits.
    Astronomy and Astrophysics 01/2002; 396:1037-1044. · 5.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Rapid granular flows have applications to many geophysical phenomena, such as snow avalanches and rockfalls. Kinetic theories are available which describe these flows as a continuum, based on an analogy between the motion of molecules in a gas and the motion of the particles in a granular flow. The governing equations arising from these theories are similar in structure to those which describe the conservation of mass and momentum in a compressible Newtonian fluid, but are supplemented by an expression for the conservation of fluctuation energy. We have developed a shallow layer, depth-averaged model from these equations for exploring the evolution of a rapid granular flow down a slope. In the process of depth- averaging, approximations have to be made about the functional form of certain terms. For example, it is necessary to express the total dissipation of fluctuation energy (due to inelastic collisions) in the layer as a function of mass flux, mean velocity, and mean fluctuation energy. In order to achieve this, we have determined some general relation- ships from numerical investigation of depth profiles of steady, non-developing flows down an inclined plane. The predictions of this model for the evolution of a rapid granular flow down a slope will be presented.
    01/2002;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The ISO/SWS 1997 observations of Titan in the 600-1400 cm-1 range, where emission bands of CH3D and of methane exist, were analyzed using a radiative transfer code and an atmospheric model as described in Coustenis et al. (2001). From the best fit of the 7.7 μ m methane band we obtained a nominal temperature profile which we used - assuming values of the CH4 stratospheric abundance in the 1-3.5% range (the nominal value is 1.9%) - to find: CH3D = 6.7+2.9- 1.9 10-6 and hence a D/H ratio of 8.8 +3.2-1.9 10-5, with most of the uncertainty due to the ignorance of the exact methane abundance value. The ISO CH3D abundance and the D/H ratio are in good agreement with results from ground-based observations by Orton (1992), who found a D/H ratio of 7.75 +/- 2.25 10-5, and by Coustenis et al. (1993) who reported similar values from data obtained in 1992 with IRSHELL/IRTF and calibrated against the Voyager observations. Recently, by re-calibrating this data with ISO, we find a CH3D / CH4 measure of 3.2 10-4, from which we find a preliminary best fit value of D/H to be about 7.9 10-5. This work is in progress and aims to improve the D/H ratio determination significantly by combining all the data. Indeed, it appears that we may be reaching a consensus on the D/H value. The Voyager 1 value (Coustenis et al., 1989), of 1.5 +1.4-0.5 10-4, is higher, but still compatible with the upper limits of the ISO and IRSHELL data. Based on these results new constraints may be set on cosmogonical scenarios such as the one proposed by Mousis et al. (2001) which suggests among other that the atmospheric CH4 is continuously replenished by outgassing from the interior of Titan. References: - Coustenis, A., et al., 1993. XVIII EGS Assembly, Wiesbaden, Germany, 3-7 May, Proceedings in Ann. Geoph., Springer Intern. Eds, Vol. 11, p. C460. - Coustenis, A., et al., 1989. Icarus 82, 67. - Coustenis, A., et al., 2001. Submitted for publication. - Mousis, O., et al., 2001. Submitted for publication in Icarus. See also paper in this DPS meeting. - Orton, G. 1992. Proc. of the Titan Symp., Toulouse, France, 9-12 Sept. 1991. ESA-SP 338, 81.
    10/2001; 33:1108.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: After a first view of Titan obtained by the Voyager missions in the 1980s, Saturn's largest satellite remains a mysterious object. In particular, its lower atmosphere and surface are still largely unknown. The degree of complexity achieved by the chemistry in its stratosphere has not been clearly evaluated by previous space missions, due to low spectral resolution and/or sensitivity. With ISO, in 1997, we have enhanced our knowledge of the chemical composition of the atmosphere, but have failed to acquire full scans in the submm range, where the Saturnian straylight was too important. The CIRS instrument aboard the Cassini mission will considerably increase our knowledge in 2004, but may well be complemented by FIRST observations in 2007, thanks to the higher resolution and sensitivity that PACS, SPIRE and HIFI have to offer.
    06/2001; 460:393.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the far-infrared spectrum of Jupiter that was measured with the Short and Long Wavelength Spectrometers (SWS and LWS) aboard the Infrared Space Observatory (ISO). The region between 38 and 44 microns was observed in grating mode, where the SWS provides a spectral resolution of about 1300. For longer waves up to 197 microns the LWS-FP (Fabry-Perot) was used to achieve a resolution of several thousand. The observations were made between 23 and 26 May 1997 during ISO's revolutions 554, 556 and 557. The Jovian spectrum in the far-infrared is compared to an atmospheric radiative transfer model using expected values for the vertical profiles of the atmospheric constituents. Rotational transitions of ammonia and phosphine are responsible for the absorption features observed: Strong ammonia absorption manifolds are obvious against the background continuum slope, appearing at 39, 42, 46, 51, 56, 63, 72, 84, 100 and 125 microns in both the data and the model. Also PH3 features are present at the expected wavelengths of 113 and 141 microns in both the data and the model. This is the first time that most of these far-infrared features have been detected. The ISO observations are therefore of interest for the preparation of the planned submillimeter studies of the atmospheres of the Jovian planets with FIRST.
    06/2001; 460:365.

Publication Stats

794 Citations
208.08 Total Impact Points

Institutions

  • 1983–2007
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1995–2005
    • University of Michigan
      • Department of Atmospheric, Oceanic and Space Sciences
      Ann Arbor, MI, United States
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2002
    • University of Texas at Austin
      • Department of Astronomy
      Texas City, TX, United States
  • 2000
    • University of Lethbridge
      • Department of Physics
      Lethbridge, Alberta, Canada
  • 1999
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
    • University of Saskatchewan
      Saskatoon, Saskatchewan, Canada
  • 1977–1982
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France