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Saint-Sauveur-en-Rue, France

Tepfer D.,French National Institute for Agricultural Research | Zalar A.,University of Versailles | Leach S.,LERMA
Astrobiology | Year: 2012

The plausibility that life was imported to Earth from elsewhere can be tested by subjecting life-forms to space travel. Ultraviolet light is the major liability in short-term exposures (Horneck et al., 2001), and plant seeds, tardigrades, and lichens-but not microorganisms and their spores-are candidates for long-term survival (Anikeeva et al., 1990; Sancho et al., 2007; Jönsson et al., 2008; de la Torre et al., 2010). In the present study, plant seeds germinated after 1.5 years of exposure to solar UV, solar and galactic cosmic radiation, temperature fluctuations, and space vacuum outside the International Space Station. Of the 2100 exposed wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds, 23% produced viable plants after return to Earth. Survival was lower in the Arabidopsis Wassilewskija ecotype and in mutants (tt4-8 and fah1-2) lacking UV screens. The highest survival occurred in tobacco (44%). Germination was delayed in seeds shielded from solar light, yet full survival was attained, which indicates that longer space travel would be possible for seeds embedded in an opaque matrix. We conclude that a naked, seed-like entity could have survived exposure to solar UV radiation during a hypothetical transfer from Mars to Earth. Chemical samples of seed flavonoid UV screens were degraded by UV, but their overall capacity to absorb UV was retained. Naked DNA encoding the nptII gene (kanamycin resistance) was also degraded by UV. A fragment, however, was detected by the polymerase chain reaction, and the gene survived in space when protected from UV. Even if seeds do not survive, components (e.g., their DNA) might survive transfer over cosmic distances. Key Words: Origin of life-Panspermia-Plant seeds-Flavonoid UV screens-DNA degradation-UV resistance-International Space Station. Astrobiology 12, 517-528. © Mary Ann Liebert, Inc. Source

Mahfouf J.-F.,Meteo - France | Birman C.,Meteo - France | Aires F.,ESTELLUS | Prigent C.,LERMA | And 2 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2015

This study examines the information content on atmospheric temperature and humidity profiles that could be provided by a future spaceborne microwave sensor with a few hundred radiances in the millimetre and submillimetre spectral domains (ranging from 7-800 GHz). A channel selection method based on optimal estimation theory is undertaken, using a database of profiles with associated errors from the European Centre for Medium-Range Weather Forecasts (ECMWF) numerical weather prediction model and the radiative transfer model Atmospheric Radiative Transfer Simulator (ARTS) under clear-sky conditions. The main results indicate that, by increasing the number of channels within the oxygen absorption band around 60 GHz and within the water-vapour absorption band at 183 GHz, the accuracy of temperature and humidity retrievals in the troposphere and stratosphere (for temperature) would be noticeably improved compared with present and planned microwave radiometers. The channels located in the absorption lines at 118 GHz and above 200 GHz do not bring significant additional information regarding atmospheric profiles under clear-sky conditions, partly due to greater radiometric noise. With a set of 137 selected channels that contribute to 90% of the total information content (measured by the degree of freedom for signal), it is possible to achieve almost the same performance in terms of variance error reduction as with 276 candidate channels. Sensitivity studies of various prescribed quantities defining the channel selection have been undertaken, in order to check the robustness of the conclusions. They show that none of the choices modifies the above findings. © 2015 Royal Meteorological Society. Source

Guzman V.V.,Harvard - Smithsonian Center for Astrophysics | Pety J.,Institute Of Radioastronomie Millimetrique Iram | Goicoechea J.R.,CSIC - Institute of Materials Science | Gerin M.,LERMA | And 6 more authors.
Astrophysical Journal Letters | Year: 2015

Small hydrocarbons, such as C2H, C3H, and C3H2 are more abundant in photo-dissociation regions (PDRs) than expected based on gas-phase chemical models. To explore the hydrocarbon chemistry further, we observed a key intermediate species, the hydrocarbon ion l-C3H+, in the Horsehead PDR with the Plateau de Bure Interferometer at high-angular resolution (6″). We compare with previous observations of C2H and c-C3H2 at similar angular resolution and new gas-phase chemical model predictions to constrain the dominant formation mechanisms of small hydrocarbons in low-UV flux PDRs. We find that at the peak of the HCO emission (PDR position), the measured l-C3H+, C2H, and c-C3H2 abundances are consistent with current gas-phase model predictions. However, in the first PDR layers, at the 7.7 μm polycyclic aromatic hydrocarbon band emission peak, which are more exposed to the radiation field and where the density is lower, the C2H and c-C3H2 abundances are underestimated by an order of magnitude. At this position, the l-C3H+ abundance is also underpredicted by the model but only by a factor of a few. In addition, contrary to the model predictions, l-C3H+ peaks further out in the PDR than the other hydrocarbons, C2H and c-C3H2. This cannot be explained by an excitation effect. Current gas-phase photochemical models thus cannot explain the observed abundances of hydrocarbons, in particular, in the first PDR layers. Our observations are consistent with a top-down hydrocarbon chemistry, in which large polyatomic molecules or small carbonaceous grains are photo-destroyed into smaller hydrocarbon molecules/precursors. © 2015. The American Astronomical Society. All rights reserved.. Source

Mueller B.,ETH Zurich | Hirschi M.,ETH Zurich | Jimenez C.,LERMA | Ciais P.,CEA Saclay Nuclear Research Center | And 14 more authors.
Hydrology and Earth System Sciences | Year: 2013

Land evapotranspiration (ET) estimates are available from several global data sets.Here, Monthly Global Land et Synthesis Products, Merged from These Individual Data Sets over the Time Periods 1989-1995 (7 Yr) and 1989-2005 (17 Yr), Are Presented. the Merged Synthesis Products over the Shorter Period Are Based on A Total of 40 Distinct Data Sets while Those over the Longer Period Are Based on A Total of 14 Data Sets. in the Individual Data Sets, et Is Derived from Satellite And/or in Situ Observations (Diagnostic Data Sets) or Calculated Via Land-surface Models (LSMs) Driven with Observations-based Forcing or Output from Atmospheric Reanalyses. Statistics for Four Merged Synthesis Products Are Provided, One Including All Data Sets and Three Including only Data Sets from One Category Each (Diagnostic, LSMs, and Reanalyses). the Multi-annual Variations of et in the Merged Synthesis Products Display Realistic Responses. They Are Also Consistent with Previous Findings of A Global Increase in et between 1989 and 1997 (0.13 Mm yr-2 in Our Merged Product) Followed by A Significant Decrease in This Trend (-0.18 Mm yr-2), although These Trends Are Relatively Small Compared to the Uncertainty of Absolute et Values. the Global Mean et from the Merged Synthesis Products (Based on All Data Sets) Is 493 Mm yr-1 (1.35 Mm d-1) for Both the 1989-1995 and 1989-2005 Products, Which Is Relatively Low Compared to Previously Published Estimates. We Estimate Global Runoff (Precipitation Minus ET) to 263 Mm yr -1 (34 406 km3 yr-1) for A Total Land Area of 130 922 000 km2. Precipitation, Being An Important Driving Factor and Input to Most Simulated et Data Sets, Presents Uncertainties between Single Data Sets As Large As Those in the et Estimates. in Order to Reduce Uncertainties in Current et Products, Improving the Accuracy of the Input Variables, Especially Precipitation, As Well As the Parameterizations of ET, Are Crucial. © 2013 Author(s). Source

Stoecklin T.,CNRS Institute of Molecular Sciences | Bussery-Honvault B.,Laboratory Interdisciplinaire Carnot de Bourgogne | Honvault P.,Laboratory Interdisciplinaire Carnot de Bourgogne | Dayou F.,LERMA
Computational and Theoretical Chemistry | Year: 2012

New long-range multipolar coefficients for the X+OH(X 2Π) interactions, where X=O( 3P), S( 3P) and N( 4S), are given here. They have been evaluated on the basis of monomer properties of the atoms and OH such as the dipole and quadrupole moments, and the static and dynamic polarizabilities. Each matrix element of the 18×18 (8×8 for N+OH) quasi-degenerate asymptotic potentials has been built up by means of the perturbation theory up to second order including or not the fine-structure of O, S and OH. The adiabatic potentials, obtained after diagonalization of the full matrix, show many crossings and complex behaviors near the asymptotes. Using the entrance channel ground state potential, the "adiabatic capture in the centrifugal sudden approximation" (ACCSA) approach has been found very convenient to get upper limit rate constants for the X+OH→XO+H reactions together with their temperature dependence. It is particularly sensitive to the long-range part of the potential in the low temperature regime. Three types of ground state potentials have been used to evaluate the influence of the potential on the magnitude and temperature dependence of the rate constants: one is obtained by supermolecular ab initio calculations and the other two by perturbation theory including or not the spin-orbit splittings. According to the potential which is employed, different behaviors of the rate constants are observed in the low and high temperature ranges while their absolute values are close in the middle temperature range. The ACCSA rate constants overestimate, by a factor of 2, more accurate kinetic values derived from quasi-classical and quantum dynamical calculations performed with global potential energy surfaces. This is attributed to a significant lower reaction probability than the one accounted for in the capture approximation employed here. © 2012 Elsevier B.V. Source

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