^1,2P. R. McCullough, ^1,3N. Crouzet, ^4,5D. Deming, and ^6,7N. Madhusudhan

¹ Space Telescope Science Institute, Baltimore, MD 21218, USA
² Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
³ Dunlap Institute for Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario M5S 3H4, Canada
⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁵ NASA Astrobiology Institute’s Virtual Planetary Laboratory
⁶ Yale Center for Astronomy & Astrophysics, Yale University, New Haven, CT 06511, USA
⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK

We report near-infrared spectroscopy of the gas giant planet HD 189733b in transit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) with its G141 grism covering 1.1 μm to 1.7 μm and spatially scanned the image across the detector at 2” s–1. When smoothed to 75 nm bins, the local maxima of the transit depths in the 1.15 μm and 1.4 μm water vapor features are, respectively, 83 ± 53 ppm and 200 ± 47 ppm greater than the local minimum at 1.3 μm. We compare the WFC3 spectrum with the composite transit spectrum of HD 189733b assembled by Pont et al., extending from 0.3 μm to 24 μm. Although the water vapor features in the WFC3 spectrum are compatible with the model of non-absorbing, Rayleigh-scattering dust in the planetary atmosphere, we also re-interpret the available data with a clear planetary atmosphere. In the latter interpretation, the slope of increasing transit depth with shorter wavelengths from the near infrared, through the visible, and into the ultraviolet is caused by unocculted star spots, with a smaller contribution of Rayleigh scattering by molecular hydrogen in the planet’s atmosphere. At relevant pressures along the terminator, our model planetary atmosphere’s temperature is ~700 K, which is below the condensation temperatures of sodium- and potassium-bearing molecules, causing the broad wings of the spectral lines of Na I and K I at 0.589 μm and 0.769 μm to be weak.

Reference
McCullough RP, Crouzet N, Deming D, Madhusudhan N (2014) Water Vapor in the Spectrum of the Extrasolar Planet HD 189733b. I. The Transit. The Astrophysical Journal 791, 55.

Link to Article: [doi:10.1088/0004-637X/791/1/55]

^1,2O. Poch, ¹S. Kaci, ¹F. Stalport, ³C. Szopa, ^1,4P. Coll

¹ LISA, UMR CNRS 7583, Université Paris Est Créteil, Université Paris Diderot, Institut Pierre Simon Laplace, 61 avenue du Général de Gaulle, 94010 Créteil cedex, France
² Center for Space and Habitability, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
³ Université Versailles St-Quentin;Sorbonne Universités, UPMC Univ. Paris 06;CNRS/INSU, LATMOS-IPSL, Quartier des Garennes, 11 Boulevard d’Alembert, 78230 Guyancourt, France
⁴ Institut Universitaire de France, 103 bld St-Michel, 75005 Paris, France

The search for organic carbon at the surface of Mars, as clues of past habitability or remnants of life, is a major science goal of Mars’ exploration. Understanding the chemical evolution of organic molecules under current Martian environmental conditions is essential to support the analyses performed in situ. What molecule can be preserved? What is the timescale of organic evolution at the surface? This paper presents the results of laboratory investigations dedicated to monitor the evolution of organic molecules when submitted to simulated Mars surface ultraviolet radiation (190-400 nm), mean temperature (218 ± 2 K) and pressure (6 ± 1 mbar) conditions. Experiments are done with the MOMIE simulation setup (for Mars Organic Molecules Irradiation and Evolution) allowing both a qualitative and quantitative characterization of the evolution the tested molecules undergo ( Poch et al., 2013). The chemical structures of the solid products and the kinetic parameters of the photoreaction (photolysis rate, half-life and quantum efficiency of photodecomposition) are determined for glycine, urea, adenine and chrysene. Mellitic trianhydride is also studied in order to complete a previous study done with mellitic acid ( Stalport et al., 2009), by studying the evolution of mellitic trianhydride. The results show that solid layers of the studied molecules have half-lives of 10 to 103 hours at the surface of Mars, when exposed directly to Martian UV radiation. However, organic layers having aromatic moieties and reactive chemical groups, as adenine and mellitic acid, lead to the formation of photoresistant solid residues, probably of macromolecular nature, which could exhibit a longer photostability. Such solid organic layers are found in micrometeorites or could have been formed endogenously on Mars. Finally, the quantum efficiencies of photodecomposition at wavelengths from 200 to 250 nm, determined for each of the studied molecules, range from 10-2 to 10-6 molecule photon-1 and apply for isolated molecules exposed at the surface of Mars. These kinetic parameters provide essential inputs for numerical modeling of the evolution of Mars’ current reservoir of organic molecules. Organic molecules adsorbed on Martian minerals may have different kinetic parameters and lead to different endproducts. The present study paves the way for the interpretation of more complex simulation experiments where organics will be mixed with Martian mineral analogs.

Reference
Poch O, Kaci S, Stalport F, Szopa C, Coll P (2014) Laboratory insights into the chemical and kinetic evolution of several organic molecules under simulated Mars surface UV radiation conditions. Icarus (in Press)

Link to Article [DOI: 10.1016/j.icarus.2014.07.014]

Corpyright Elsevier

¹E. Charon, ²J. Aléon, ³J.- N. Rouzaud

¹ Centre de Sciences Nucléaires et de Sciences de la Matière, CNRS/IN2P3 – Université Paris Sud XI, UMR CNRS 8609, Bât 104 91405 Orsay Campus, France
² Laboratoire de Géologie, UMR CNRS 8538, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 5, France
³ Present address: CEA Saclay, DSM/IRAMIS/ NIMBE Laboratoire Edifices Nanométriques, Bat 522, 91191 Gif sur Yvette, France

The structure and nanostructures of carbon phases from the Acapulco and Lodran meteorites and their carbon and nitrogen isotopic composition were investigated at the nanometer and micrometer scale using a systematic combination of Raman microspectrometry, high-resolution transmission electron microscopy and secondary ion mass spectrometry to determine their origin and thermal evolution. Several morphological types were recognized belonging to roughly two isotopic and structural families: coarse carbon grains and rosettes on one hand, only found in Acapulco, and vein-like carbon occurrences on the other hand present in both Acapulco and Lodran. Carbon phases in Acapulco are highly graphitized, and show a genetic relationship with metal indicative of metal-assisted graphitization. By contrast, carbon phases in Lodran are exclusively disordered mesoporous turbostratic carbons, in spite of their inclusion in metal and the higher peak temperature experienced by the Lodran parent body. δ13C values range between -59‰ and +37‰ in Acapulco and between -38‰ and -1‰ in Lodran and show in both cases a peak in their distribution at the value of chondritic insoluble organic matter (IOM, -10 to -15‰). N concentrations together with δ15N values indicate a mixing between a component akin to chondritic IOM in Lodran with a δ15N value around +10 – +20‰ and a component akin to that in the most N-poor Acapulco graphites. The latter are systematically depleted in 15N with a δ15N value constant at ∼ -140‰ for N concentrations below ∼ 1.4 wt%.

These observations can be explained if carbon phases in Acapulco and Lodran result from the late impact introduction of CI-CM like IOM, after significant cooling of the parent-body, and subsequent carbonization and graphitization of IOM by interaction with FeNi metal by the heat wave induced by the impact. Temperatures probably reached 900°C in Acapulco, enough to achieve metal-assisted graphitization but were not significantly higher than 650°C in Lodran. Carbon phases in Lodran would have been formed by the secondary carbonization of hydrocarbon fluids released during the primary carbonization of IOM. In the framework of this model, the C isotopic compositions can be reproduced using Rayleigh distillation at each carbonization step and the N isotopic compositions can be understood as resulting from the variable loss and preservation of 15N-rich nitriles (δ15N ∼ +800‰) and 15N-poor pyrroles (δ15N = -140‰) during carbonization. The combined interpretation of the temperatures deduced from this model, petrographic cooling rates, and thermochronological indicators suggest that the CI-CM IOM could have been introduced in the parent-body by an impact, about 10 Myr after solar system formation.

Reference
Charon E, Aléon J., Rouzaud N (2014) Impact delivery of organic matter on the acapulcoite-lodranite parent-body deduced from C, N isotopes and nanostructures of carbon phases in Acapulco and Lodran. Geochimica et Cosmochimica Acta (in Press)

Link to Article [DOI: 10.1016/j.gca.2014.07.009]

Copyright Elsevier