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Nixon CA. The Composition and Chemistry of Titan's Atmosphere. ACS EARTH & SPACE CHEMISTRY 2024; 8:406-456. [PMID: 38533193 PMCID: PMC10961852 DOI: 10.1021/acsearthspacechem.2c00041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 11/02/2023] [Accepted: 02/02/2024] [Indexed: 03/28/2024]
Abstract
In this review I summarize the current state of knowledge about the composition of Titan's atmosphere and our current understanding of the suggested chemistry that leads to that observed composition. I begin with our present knowledge of the atmospheric composition, garnered from a variety of measurements including Cassini-Huygens, the Atacama Large Millimeter/submillimeter Array, and other ground- and space-based telescopes. This review focuses on the typical vertical profiles of gases at low latitudes rather than global and temporal variations. The main body of the review presents a chemical description of how complex molecules are believed to arise from simpler species, considering all known "stable" molecules-those that have been uniquely identified in the neutral atmosphere. The last section of the review is devoted to the gaps in our present knowledge of Titan's chemical composition and how further work may fill those gaps.
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Affiliation(s)
- Conor A. Nixon
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, United
States
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2
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Blitz MA, Onel L, Robertson SH, Seakins PW. Studies on the Kinetics of the CH + H 2 Reaction and Implications for the Reverse Reaction, 3CH 2 + H. J Phys Chem A 2023; 127:2367-2375. [PMID: 36857400 PMCID: PMC10026075 DOI: 10.1021/acs.jpca.2c08097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2023]
Abstract
The reaction of CH radicals with H2 has been studied by the use of laser flash photolysis, probing CH decays under pseudo-first-order conditions using laser-induced fluorescence (LIF) over the temperature range 298-748 K at pressures of ∼5-100 Torr. Careful data analysis was required to separate the CH LIF signal at ∼428 nm from broad background fluorescence, and this interference increased with temperature. We believe that this interference may have been the source of anomalous pressure behavior reported previously in the literature (Brownsword, R. A.; J. Chem. Phys. 1997, 106, 7662-7677). The rate coefficient k1 shows complex behavior: at low pressures, the main route for the CH3* formed from the insertion of CH into H2 is the formation of 3CH2 + H, and as the pressure is increased, CH3* is increasingly stabilized to CH3. The kinetic data on CH + H2 have been combined with experimental shock tube data on methyl decomposition and literature thermochemistry within a master equation program to precisely determine the rate coefficient of the reverse reaction, 3CH2 + H → CH + H2. The resulting parametrization is kCH2+H(T) = (1.69 ± 0.11) × 10-10 × (T/298 K)(0.05±0.010) cm3 molecule-1 s-1, where the errors are 1σ.
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Affiliation(s)
- Mark A Blitz
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
- NCAS, University of Leeds, Leeds LS2 9JT, U.K
| | - Lavinia Onel
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | | | - Paul W Seakins
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
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Thompson MA, Krissansen-Totton J, Wogan N, Telus M, Fortney JJ. The case and context for atmospheric methane as an exoplanet biosignature. Proc Natl Acad Sci U S A 2022; 119:e2117933119. [PMID: 35353627 PMCID: PMC9168929 DOI: 10.1073/pnas.2117933119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Accepted: 01/31/2022] [Indexed: 11/24/2022] Open
Abstract
Methane has been proposed as an exoplanet biosignature. Imminent observations with the James Webb Space Telescope may enable methane detections on potentially habitable exoplanets, so it is essential to assess in what planetary contexts methane is a compelling biosignature. Methane’s short photochemical lifetime in terrestrial planet atmospheres implies that abundant methane requires large replenishment fluxes. While methane can be produced by a variety of abiotic mechanisms such as outgassing, serpentinizing reactions, and impacts, we argue that—in contrast to an Earth-like biosphere—known abiotic processes cannot easily generate atmospheres rich in CH4 and CO2 with limited CO due to the strong redox disequilibrium between CH4 and CO2. Methane is thus more likely to be biogenic for planets with 1) a terrestrial bulk density, high mean-molecular-weight and anoxic atmosphere, and an old host star; 2) an abundance of CH4 that implies surface fluxes exceeding what could be supplied by abiotic processes; and 3) atmospheric CO2 with comparatively little CO.
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Affiliation(s)
- Maggie A. Thompson
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064
| | | | - Nicholas Wogan
- Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195
| | - Myriam Telus
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064
| | - Jonathan J. Fortney
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064
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Mancini L, Vanuzzo G, Marchione D, Pannacci G, Liang P, Recio P, Rosi M, Skouteris D, Casavecchia P, Balucani N. The Reaction N( 2D) + CH 3CCH (Methylacetylene): A Combined Crossed Molecular Beams and Theoretical Investigation and Implications for the Atmosphere of Titan. J Phys Chem A 2021; 125:8846-8859. [PMID: 34609869 PMCID: PMC8521525 DOI: 10.1021/acs.jpca.1c06537] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The reaction of excited
nitrogen atoms N(2D) with CH3CCH (methylacetylene)
was investigated under single-collision
conditions by the crossed molecular beams (CMB) scattering method
with mass spectrometric detection and time-of-flight analysis at the
collision energy (Ec) of 31.0 kJ/mol.
Synergistic electronic structure calculations of the doublet potential
energy surface (PES) were performed to assist the interpretation of
the experimental results and characterize the overall reaction micromechanism.
Theoretically, the reaction is found to proceed via a barrierless addition of N(2D) to the carbon–carbon
triple bond of CH3CCH and an insertion of N(2D) into the CH bond of the methyl group, followed
by the formation of cyclic and linear intermediates that can undergo
H, CH3, and C2H elimination or isomerize to
other intermediates before unimolecularly decaying to a variety of
products. Kinetic calculations for addition and insertion mechanisms
and statistical (Rice-Ramsperger-Kassel-Marcus) computations of product
branching fractions (BFs) on the theoretical PES were performed at
different values of total energy, including the one corresponding
to the temperature (175 K) of Titan’s stratosphere and that
of the CMB experiment. Up to 14 competing product channels were statistically
predicted, with the main ones, at Ec =
31.0 kJ/mol, being the formation of CH2NH (methanimine)
+ C2H (ethylidyne) (BF = 0.41), c-C(N)CH
+ CH3 (BF = 0.32), CH2CHCN (acrylonitrile) +
H (BF = 0.12), and c-CH2C(N)CH + H (BF
= 0.04). Of the 14 possible channels, seven correspond to H displacement
channels of different exothermicity, for a total H channel BF of ∼0.25
at Ec = 31.0 kJ/mol. Experimentally, dynamical
information could only be obtained about the overall H channels. In
particular, the experiment corroborates the formation of acrylonitrile
+ H, which is the most exothermic of all 14 reaction channels and
is theoretically calculated to be the dominant H-forming channel (BF
= 0.12). The products containing a novel C–N bond could be
potential precursors to form other nitriles (C2N2, C3N) or more complex organic species containing N atoms
in planetary atmospheres, such as those of Titan and Pluto. Overall,
the results are expected to have a potentially significant impact
on the understanding of the gas-phase chemistry of Titan’s
atmosphere and the modeling of that atmosphere.
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Affiliation(s)
- Luca Mancini
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Gianmarco Vanuzzo
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Demian Marchione
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Giacomo Pannacci
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Pengxiao Liang
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Pedro Recio
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Marzio Rosi
- Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Perugia, 06125 Perugia, Italy
| | | | - Piergiorgio Casavecchia
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
| | - Nadia Balucani
- Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy
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Mouzay J, Piétri N, Couturier-Tamburelli I, Chiavassa T. UV irradiation of benzene in N2 matrix: A relevant study for titan's chemistry. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2021.130296] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Messinger JP, Gupta D, Cooke IR, Okumura M, Sims IR. Rate Constants of the CN + Toluene Reaction from 15 to 294 K and Interstellar Implications. J Phys Chem A 2020; 124:7950-7958. [DOI: 10.1021/acs.jpca.0c06900] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Joseph P. Messinger
- Arthur Amos Noyes Laboratory of Chemical Physics, Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
- Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
| | - Divita Gupta
- Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
| | - Ilsa R. Cooke
- Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
| | - Mitchio Okumura
- Arthur Amos Noyes Laboratory of Chemical Physics, Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Ian R. Sims
- Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
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On an EUV Atmospheric Simulation Chamber to Study the Photochemical Processes of Titan's Atmosphere. Sci Rep 2020; 10:10009. [PMID: 32561886 PMCID: PMC7305212 DOI: 10.1038/s41598-020-66950-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 06/01/2020] [Indexed: 11/16/2022] Open
Abstract
The in situ exploration of Titan’s atmosphere requires the development of laboratory experiments to understand the molecular growth pathways initiated by photochemistry in the upper layers of the atmosphere. Key species and dominant reaction pathways are used to feed chemical network models that reproduce the chemical and physical processes of this complex environment. Energetic UV photons initiate highly efficient chemistry by forming reactive species in the ionospheres of the satellite. We present here a laboratory experiment based on a new closed and removable photoreactor coupled here to an Extreme Ultraviolet (EUV) irradiation beam produced by the high-order harmonic generation of a femtosecond laser. This type of EUV stable source allow long-term irradiation experiments in which a plethora of individual reactions can take place. In order to demonstrate the validity of our approach, we irradiated for 7 hours at 89.2 nm, a gas mixture based on N2/CH4 (5%). Using only one wavelength, products of the reaction reveal an efficient photochemistry with the formation of large hydrocarbons but especially organic compounds rich in nitrogen similar to Titan. Among these nitrogen compounds, new species had never before been identified in the mass spectra obtained in situ in Titan’s atmosphere. Their production in this experiment, on the opposite, corroborates previous experimental measurements in the literature on the chemical composition of aerosol analogues produced in the laboratory. Diazo-compounds such as dimethyldiazene (C2H6N2), have been observed and are consistent with the large nitrogen incorporation observed by the aerosols collector pyrolysis instrument of the Huygens probe. This work represents an important step forward in the use of a closed cell chamber irradiated by the innovative EUV source for the generation of photochemical analogues of Titan aerosols. This approach allows to better constrain and understand the growth pathways of nitrogen incorporation into organic aerosols in Titan’s atmosphere.
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8
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Muller G, Jacovella U, Catani KJ, da Silva G, Bieske EJ. Electronic Spectrum and Photodissociation Chemistry of the 1-Butyn-3-yl Cation, H 3CCHCCH . J Phys Chem A 2020; 124:2366-2371. [PMID: 32119779 DOI: 10.1021/acs.jpca.9b11810] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The B̃1A' ← X̃1A' electronic spectra of the 1-butyn-3-yl cation (H3CCHCCH+) and the H3CCHCCH+-Ne and H3CCHCCH+-Ar complexes are measured using resonance enhanced photodissociation over the 245-285 nm range, with origin transitions occurring at 35936, 35930, and 35928 cm-1, respectively. Vibronic bands are assigned based on quantum chemical calculations and comparison of the spectra with those of the related linear methyl propargyl (H3C4H2+) and propargyl (H2C3H+) cations. The photofragment ions are C2H3+ (major) and C4H3+ (minor), with the preference for C2H3+ consistent with master equation simulations for a mechanism that involves rapid electronic deactivation and dissociation on the ground state potential energy surface.
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Affiliation(s)
- Giel Muller
- School of Chemistry, The University of Melbourne, Melbourne, Victoria, Australia 3010
| | - Ugo Jacovella
- School of Chemistry, The University of Melbourne, Melbourne, Victoria, Australia 3010
| | - Katherine J Catani
- School of Chemistry, The University of Melbourne, Melbourne, Victoria, Australia 3010
| | - Gabriel da Silva
- Department of Chemical Engineering, The University of Melbourne, Melbourne, Victoria, Australia 3010
| | - Evan J Bieske
- School of Chemistry, The University of Melbourne, Melbourne, Victoria, Australia 3010
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9
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Hendrix J, Bera PP, Lee TJ, Head-Gordon M. Cation, Anion, and Radical Isomers of C 4H 4N: Computational Characterization and Implications for Astrophysical and Planetary Environments. J Phys Chem A 2020; 124:2001-2013. [PMID: 32077700 DOI: 10.1021/acs.jpca.9b11305] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Nitrogen-containing ions and molecules in the gas phase have been detected in non-Earth environments such as dark molecular clouds and more recently in the atmosphere of Saturn's moon Titan. These molecules may serve as precursors to larger heterocyclic structures that provide the foundation of complex biological molecules. On Titan, molecules of m/z 66 have been detected by the Cassini mission, and species of the empirical formula C4H4N may contribute to this signature. We have characterized seven isomers of C4H4N in anionic, neutral radical, and cationic states using density functional theory. Structures were optimized using the range-separated hybrid ωB97X-V with the cc-pVTZ and aug-cc-pVTZ basis sets. Anionic and radical C4H4N favor cyclic structures with aromatic and quasi-aromatic electron arrangements, respectively. Interestingly, ionization from the radical surface to the cation induces significant changes in structural stability, and the global minimum for positively charged isomers is CH2CCHCNH+, a pseudo-linear species reminiscent of cyanoallene. Select formation pathways to these structures from Titan's existing or postulated gas-phase species, reactions that are also relevant for other astrophysical environments, are discussed. By characterizing C4H4N isomers, we have identified energetically stable anionic, radical, and cationic structures that may be present in Titan's atmosphere and dark molecular clouds.
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Affiliation(s)
- Josie Hendrix
- Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Partha P Bera
- NASA Ames Research Center, Moffett Field, Mountain View, California 94035, United States.,Bay Area Environmental Research Institute, Moffett Field, Mountain View, California 94952, United States
| | - Timothy J Lee
- NASA Ames Research Center, Moffett Field, Mountain View, California 94035, United States
| | - Martin Head-Gordon
- Department of Chemistry, University of California, Berkeley, California 94720, United States
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10
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Martin KP, MacKenzie SM, Barnes JW, Ytreberg FM. Protein Stability in Titan's Subsurface Water Ocean. ASTROBIOLOGY 2020; 20:190-198. [PMID: 31730377 PMCID: PMC7041334 DOI: 10.1089/ast.2018.1972] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 10/08/2019] [Indexed: 06/10/2023]
Abstract
Models of Titan predict that there is a subsurface ocean of water and ammonia under a layer of ice. Such an ocean would be important in the search for extraterrestrial life since it provides a potentially habitable environment. To evaluate how Earth-based proteins would behave in Titan's subsurface ocean environment, we used molecular dynamics simulations to calculate the properties of proteins with the most common secondary structure types (alpha helix and beta sheet) in both Earth and Titan-like conditions. The Titan environment was simulated by using a temperature of 300 K, a pressure of 1000 bar, and a eutectic mixture of water and ammonia. We analyzed protein compactness, flexibility, and backbone dihedral distributions to identify differences between the two environments. Secondary structures in the Titan environment were found to be less long-lasting, less flexible, and had small differences in backbone dihedral preferences (e.g., in one instance a pi helix formed). These environment-driven differences could lead to changes in how these proteins interact with other biomolecules and therefore changes in how evolution would potentially shape proteins to function in subsurface ocean environments.
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Affiliation(s)
- Kyle P. Martin
- Department of Physics, University of Idaho, Moscow, Idaho
- Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho
| | | | | | - F. Marty Ytreberg
- Department of Physics, University of Idaho, Moscow, Idaho
- Institute for Modeling Collaboration and Innovation, University of Idaho, Moscow, Idaho
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11
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Teanby NA, Sylvestre M, Sharkey J, Nixon CA, Vinatier S, Irwin PGJ. Seasonal evolution of Titan's stratosphere during the Cassini mission. GEOPHYSICAL RESEARCH LETTERS 2019; 46:3079-3089. [PMID: 33100421 PMCID: PMC7580802 DOI: 10.1029/2018gl081401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Accepted: 02/19/2019] [Indexed: 06/11/2023]
Abstract
Titan's stratosphere exhibits significant seasonal changes, including break-up and formation of polar vortices. Here we present the first analysis of mid-infrared mapping observations from Cassini's Composite InfraRed Spectrometer (CIRS) to cover the entire mission (Ls=293-93°, 2004-2017) - mid-northern winter to northern summer solstice. The north-polar winter vortex persisted well after equinox, starting break-up around Ls∼60°, and fully dissipating by Ls∼90°. Absence of enriched polar air spreading to lower latitudes suggests large-scale circulation changes and photochemistry control chemical evolution during vortex break-up. South-polar vortex formation commenced soon after equinox and by Ls∼60° was more enriched in trace gases than the northern mid-winter vortex and had temperatures ∼20 K colder. This suggests early-winter and mid-winter vortices are dominated by different processes - radiative cooling and subsidence-induced adiabatic heating respectively. By the end of the mission (Ls=93°) south-polar conditions were approaching those observed in the north at Ls=293°, implying seasonal symmetry in Titan's vortices.
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Affiliation(s)
- N A Teanby
- School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK
| | - M Sylvestre
- School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK
| | - J Sharkey
- School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK
| | - C A Nixon
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
| | - S Vinatier
- LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
| | - P G J Irwin
- Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU. UK
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Contributions from Accreted Organics to Titan’s Atmosphere: New Insights from Cometary and Chondritic Data. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/aaf561] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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13
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Palmer MY, Cordiner MA, Nixon CA, Charnley SB, Teanby NA, Kisiel Z, Irwin PGJ, Mumma MJ. ALMA detection and astrobiological potential of vinyl cyanide on Titan. SCIENCE ADVANCES 2017; 3:e1700022. [PMID: 28782019 PMCID: PMC5533535 DOI: 10.1126/sciadv.1700022] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 06/27/2017] [Indexed: 06/07/2023]
Abstract
Recent simulations have indicated that vinyl cyanide is the best candidate molecule for the formation of cell membranes/vesicle structures in Titan's hydrocarbon-rich lakes and seas. Although the existence of vinyl cyanide (C2H3CN) on Titan was previously inferred using Cassini mass spectrometry, a definitive detection has been lacking until now. We report the first spectroscopic detection of vinyl cyanide in Titan's atmosphere, obtained using archival data from the Atacama Large Millimeter/submillimeter Array (ALMA), collected from February to May 2014. We detect the three strongest rotational lines of C2H3CN in the frequency range of 230 to 232 GHz, each with >4σ confidence. Radiative transfer modeling suggests that most of the C2H3CN emission originates at altitudes of ≳200 km, in agreement with recent photochemical models. The vertical column densities implied by our best-fitting models lie in the range of 3.7 × 1013 to 1.4 × 1014 cm-2. The corresponding production rate of vinyl cyanide and its saturation mole fraction imply the availability of sufficient dissolved material to form ~107 cell membranes/cm3 in Titan's sea Ligeia Mare.
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Affiliation(s)
- Maureen Y. Palmer
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
- Department of Chemistry, St. Olaf College, 1520 St. Olaf Avenue, Northfield, MN 55057, USA
- Department of Physics, Catholic University of America, Washington, DC 20064, USA
| | - Martin A. Cordiner
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
- Department of Physics, Catholic University of America, Washington, DC 20064, USA
| | - Conor A. Nixon
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
| | - Steven B. Charnley
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
| | - Nicholas A. Teanby
- School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK
| | - Zbigniew Kisiel
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikøw 32/46, 02-668 Warszawa, Poland
| | - Patrick G. J. Irwin
- Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
| | - Michael J. Mumma
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
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15
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Ren X, Pflüger T, Weyland M, Baek WY, Rabus H, Ullrich J, Dorn A. High-resolution (e, 2e + ion) study of electron-impact ionization and fragmentation of methane. J Chem Phys 2015; 142:174313. [DOI: 10.1063/1.4919691] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Li C, Zhang X, Gao P, Yung Y. VERTICAL DISTRIBUTION OF
C
3
-HYDROCARBONS IN THE STRATOSPHERE OF TITAN. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/2041-8205/803/2/l19] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Cordiner MA, Palmer MY, Nixon CA, Irwin PGJ, Teanby NA, Charnley SB, Mumma MJ, Kisiel Z, Serigano J, Kuan YJ, Chuang YL, Wang KS. ETHYL CYANIDE ON TITAN: SPECTROSCOPIC DETECTION AND MAPPING USING ALMA. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/2041-8205/800/1/l14] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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18
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Giegerich J, Fischer I. The photodissociation dynamics of alkyl radicals. J Chem Phys 2015; 142:044304. [DOI: 10.1063/1.4906605] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Jens Giegerich
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
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19
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Cordiner MA, Nixon CA, Teanby NA, Irwin PGJ, Serigano J, Charnley SB, Milam SN, Mumma MJ, Lis DC, Villanueva G, Paganini L, Kuan YJ, Remijan AJ. ALMA MEASUREMENTS OF THE HNC AND HC
3
N DISTRIBUTIONS IN TITAN'S ATMOSPHERE. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/2041-8205/795/2/l30] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Randazzo JB, Croteau P, Kostko O, Ahmed M, Boering KA. Isotope effects and spectroscopic assignments in the non-dissociative photoionization spectrum of N2. J Chem Phys 2014; 140:194303. [DOI: 10.1063/1.4873717] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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21
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Leach S, Garcia GA, Mahjoub A, Bénilan Y, Fray N, Gazeau MC, Gaie-Levrel F, Champion N, Schwell M. Ionization photophysics and spectroscopy of cyanoacetylene. J Chem Phys 2014; 140:174305. [PMID: 24811639 DOI: 10.1063/1.4871298] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11-15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC3N involves new aspects and new assignments of the vibrational components to excitation of the A(2)Σ(+) and B(2)Π states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B(2)Π state of HC3N(+). A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C(2)Σ(+) state of HC3N(+) at ≈17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6-15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C-H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised.
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Affiliation(s)
- Sydney Leach
- LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon, France
| | - Gustavo A Garcia
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, B.P. 48, 91192, Gif-sur-Yvette Cedex, France
| | - Ahmed Mahjoub
- LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil, France
| | - Yves Bénilan
- LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil, France
| | - Nicolas Fray
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, B.P. 48, 91192, Gif-sur-Yvette Cedex, France
| | - Marie-Claire Gazeau
- LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil, France
| | - François Gaie-Levrel
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, B.P. 48, 91192, Gif-sur-Yvette Cedex, France
| | - Norbert Champion
- LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon, France
| | - Martin Schwell
- LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil, France
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Peng Z, Carrasco N, Pernot P. Modeling of synchrotron-based laboratory simulations of Titan’s ionospheric photochemistry. ACTA ACUST UNITED AC 2014. [DOI: 10.1016/j.grj.2014.03.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Leach S, Schwell M, Garcia GA, Bénilan Y, Fray N, Gazeau MC, Gaie-Levrel F, Champion N, Guillemin JC. Ionization photophysics and spectroscopy of dicyanoacetylene. J Chem Phys 2013; 139:184304. [PMID: 24320271 DOI: 10.1063/1.4826467] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Photoionization of dicyanoacetylene was studied using synchrotron radiation over the excitation range 8-25 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and detailed spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of dicyanoacetylene was measured as 11.80 ± 0.01 eV. A detailed analysis of the cation spectroscopy involves new aspects and new assignments of the vibrational components to excitation of the quasi-degenerate A(2)Πg, B(2)Σg(+) states as well as the C(2)Σu(+) and D(2)Πu states of the cation. Some of the structured autoionization features observed in the 12.4-15 eV region of the total ion yield spectrum were assigned to vibrational components of valence shell transitions and to two previously unknown Rydberg series converging to the D(2)Πu state of C4N2(+). The appearance energies of the fragment ions C4N(+), C3N(+), C4(+), C2N(+), and C2(+) were measured and their heats of formation were determined and compared with existing literature values. Thermochemical calculations of the appearance potentials of these and other weaker ions were used to infer aspects of dissociative ionization pathways.
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Affiliation(s)
- Sydney Leach
- LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon, France
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YU YONGJIANG, WANG DEHUA, FENG SHUXIANG, XIA WENZE. INFLUENCE OF VIBRATIONAL EXCITATION AND COLLISION ENERGY ON THE STEREO DYNAMICS OF THE REACTIONS: N(4S)+H2(v = 0-3,j = 0) → NH(X3Σ-)+H. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2012. [DOI: 10.1142/s0219633612500514] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Quasi-classical trajectory (QCT) calculations have been carried out to study the stereodynamics of the title reactions, using the double many-body expansion (DMBE) potential energy surface (PES) constructed by Poveda [Poveda LA, Varandas AJC, Phys. Chem. Chem. Phys.7:2867, 2005]. Vector correlations, such as the distributions of the polarization-dependent differential cross-sections (PDDCSs), the angular distributions of P(θr), P(ϕr), P(θr,ϕr), and the product alignment parameter P2( cos θr) are reported within the energy range of 25–140 kcal mol-1. The influences of the collision energy and the initial state-selected vibrational excitation are discussed in detail. In addition, Validity of the current QCT calculations is also examined and compared with the revelant results reported by Pascual et al. [Pascual RZ, Schatz GC, Lendvay G, Troya D, J. Phys. Chem. Aਠ106:4125, 2002].
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Affiliation(s)
- YONG-JIANG YU
- School of Physics, Ludong University, Yantai 264025, P. R. China
| | - DE-HUA WANG
- School of Physics, Ludong University, Yantai 264025, P. R. China
| | - SHU-XIANG FENG
- School of Physics, Ludong University, Yantai 264025, P. R. China
| | - WEN-ZE XIA
- School of Physics, Ludong University, Yantai 264025, P. R. China
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Yang Y, Li Z, Zhao Y, Wan S, Liu H, Huang X, Sun C. Mechanism for the formation of benzene in the Titan’s atmosphere: A theoretical study on the mechanism of reaction. COMPUT THEOR CHEM 2012. [DOI: 10.1016/j.comptc.2012.03.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Abstract
Titan, the largest satellite of Saturn, is the only one in the solar system with a dense atmosphere. Mainly composed of dinitrogen with several % of methane, this atmosphere experiences complex organic processes, both in the gas and aerosol phases, which are of prebiotic interest and within an environment of astrobiological interest. This tutorial review presents the different approaches which can be followed to study such an exotic place and its chemistry: observation, theoretical modeling and experimental simulation. It describes the Cassini-Huygens mission, as an example of observational tools, and gives the new astrobiologically oriented vision of Titan which is now available by coupling the three approaches. This includes the many analogies between Titan and the Earth, in spite of the much lower temperature in the Saturn system, the complex organic chemistry in the atmosphere, from the gas to the aerosol phases, but also the potential organic chemistry on Titan's surface, and in its possible internal water ocean.
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Affiliation(s)
- François Raulin
- Laboratoire Interuniversitaire des Systèmes Atmosphériques, Universités Paris Est Créteil & Paris Diderot, UMR CNRS 7583, IPSL, 61 Avenue Général de Gaulle, 94010 Créteil Cedex, France.
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Trainer MG, Jimenez JL, Yung YL, Toon OB, Tolbert MA. Nitrogen incorporation in CH(4)-N(2) photochemical aerosol produced by far ultraviolet irradiation. ASTROBIOLOGY 2012; 12:315-26. [PMID: 22519972 PMCID: PMC3330558 DOI: 10.1089/ast.2011.0754] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Nitrile incorporation into Titan aerosol accompanying hydrocarbon chemistry is thought to be driven by extreme UV wavelengths (λ<120 nm) or magnetospheric electrons in the outer reaches of the atmosphere. Far UV radiation (120-200 nm), which is transmitted down to the stratosphere of Titan, is expected to affect hydrocarbon chemistry only and not initiate the formation of nitrogenated species. We examined the chemical properties of photochemical aerosol produced at far UV wavelengths, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), which allows for elemental analysis of particle-phase products. Our results show that aerosol formed from CH(4)/N(2) photochemistry contains a surprising amount of nitrogen, up to 16% by mass, a result of photolysis in the far UV. The proportion of nitrogenated organics to hydrocarbon species is shown to be correlated with that of N(2) in the irradiated gas. The aerosol mass greatly decreases when N(2) is removed, which indicates that N(2) plays a major role in aerosol production. Because direct dissociation of N(2) is highly improbable given the immeasurably low cross section at the wavelengths studied, the chemical activation of N(2) must occur via another pathway. Any chemical activation of N(2) at wavelengths >120 nm is presently unaccounted for in atmospheric photochemical models. We suggest that reaction with CH radicals produced from CH(4) photolysis may provide a mechanism for incorporating N into the molecular structure of the aerosol. Further work is needed to understand the chemistry involved, as these processes may have significant implications for how we view prebiotic chemistry on early Earth and similar planets.
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Westlake JH, Waite JH, Mandt KE, Carrasco N, Bell JM, Magee BA, Wahlund JE. Titan's ionospheric composition and structure: Photochemical modeling of Cassini INMS data. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011je003883] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Kaiser RI, Mebel AM. On the formation of polyacetylenes and cyanopolyacetylenes in Titan's atmosphere and their role in astrobiology. Chem Soc Rev 2012; 41:5490-501. [DOI: 10.1039/c2cs35068h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Jolley C, Douglas T. Topological biosignatures: large-scale structure of chemical networks from biology and astrochemistry. ASTROBIOLOGY 2012; 12:29-39. [PMID: 22204400 DOI: 10.1089/ast.2011.0674] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The chemical basis of life involves more than simply the presence of biological molecules; biochemical systems embody a complex network of reactions with characteristic topological features. At the same time, chemical complexity is also present in nonbiological contexts, inviting us to clarify the relationship between chemistry and life through comparative studies. This study examines chemical networks from biology (the metabolism of E. coli) and astronomy (gas-phase reactions in dark molecular clouds) to establish common topological features that may be generic for any complex chemical system, as well as clear differences that may be topological signatures of life. The biological and astrochemical networks exhibit different scaling behaviors, and the network motifs found in the two systems show similarities as well as significant differences. The PageRank algorithm was used to quantify the degree to which individual species act primarily as products or reactants; in the metabolic network, these two roles are nearly identical for most species, whereas the astrochemical network shows a clearer partitioning into reactants and products.
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Affiliation(s)
- Craig Jolley
- Department of Chemistry and Biochemistry and Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana, USA.
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31
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Balucani N. Elementary reactions of N atoms with hydrocarbons: first steps towards the formation of prebiotic N-containing molecules in planetary atmospheres. Chem Soc Rev 2012; 41:5473-83. [PMID: 22705670 DOI: 10.1039/c2cs35113g] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Nadia Balucani
- Dipartimento di Chimica, Università degli Studi di Perugia, Perugia, Italy.
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32
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Bell JM, Bougher SW, Waite JH, Ridley AJ, Magee BA, Mandt KE, Westlake J, DeJong AD, Bar-Nun A, Jacovi R, Toth G, De La Haye V, Gell D, Fletcher G. Simulating the one-dimensional structure of Titan's upper atmosphere: 3. Mechanisms determining methane escape. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010je003639] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
Ionizing radiation is a ubiquitous feature of the Cosmos, from exogenous cosmic rays (CR) to the intrinsic mineral radioactivity of a habitable world, and its influences on the emergence and persistence of life are wide-ranging and profound. Much attention has already been focused on the deleterious effects of ionizing radiation on organisms and the complex molecules of life, but ionizing radiation also performs many crucial functions in the generation of habitable planetary environments and the origins of life. This review surveys the role of CR and mineral radioactivity in star formation, generation of biogenic elements, and the synthesis of organic molecules and driving of prebiotic chemistry. Another major theme is the multiple layers of shielding of planetary surfaces from the flux of cosmic radiation and the various effects on a biosphere of violent but rare astrophysical events such as supernovae and gamma-ray bursts. The influences of CR can also be duplicitous, such as limiting the survival of surface life on Mars while potentially supporting a subsurface biosphere in the ocean of Europa. This review highlights the common thread that ionizing radiation forms between the disparate component disciplines of astrobiology.
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Affiliation(s)
- Lewis R Dartnell
- UCL Institute for Origins, University College London, London, UK.
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34
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Balucani N, Casavecchia P. Crossed molecular beam studies of astronomically relevant bimolecular reactions. RENDICONTI LINCEI 2011. [DOI: 10.1007/s12210-011-0128-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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35
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Atreya SK. The significance of trace constituents in the solar system. Faraday Discuss 2011; 147:9-29; discussion 83-102. [PMID: 21302540 DOI: 10.1039/c005460g] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Trace or minor constituents are key to the origin, maintenance, and the eventual fate of atmospheres of solar system objects. In this Introductory Paper, I illustrate this point by discussing certain cross cutting themes, including the chemistry of the formation and stability of a nitrogen atmosphere on Titan and the Earth, the chemical and biochemical origin of methane on the terrestrial planets and Titan, production and role of photochemical haze and aerosols, especially on Titan, and the significance of electro-photochemistry for habitability of Mars.
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Affiliation(s)
- Sushil K Atreya
- Department of Atmospheric, Oceanic, and Space Sciences Space Research Building, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA
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Bell JM, Bougher SW, Waite JH, Ridley AJ, Magee BA, Mandt KE, Westlake J, DeJong AD, De La Haye V, Bar-Nun A, Jacovi R, Toth G, Gell D, Fletcher G. Simulating the one-dimensional structure of Titan's upper atmosphere: 2. Alternative scenarios for methane escape. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010je003638] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Niemann HB, Atreya SK, Demick JE, Gautier D, Haberman JA, Harpold DN, Kasprzak WT, Lunine JI, Owen TC, Raulin F. Composition of Titan's lower atmosphere and simple surface volatiles as measured by the Cassini-Huygens probe gas chromatograph mass spectrometer experiment. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010je003659] [Citation(s) in RCA: 334] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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38
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Bell JM, Bougher SW, Waite JH, Ridley AJ, Magee BA, Mandt KE, Westlake J, DeJong AD, Bar–Nun A, Jacovi R, Toth G, De La Haye V. Simulating the one-dimensional structure of Titan's upper atmosphere: 1. Formulation of the Titan Global Ionosphere-Thermosphere Model and benchmark simulations. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010je003636] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Clark RN, Curchin JM, Barnes JW, Jaumann R, Soderblom L, Cruikshank DP, Brown RH, Rodriguez S, Lunine J, Stephan K, Hoefen TM, Le Mouélic S, Sotin C, Baines KH, Buratti BJ, Nicholson PD. Detection and mapping of hydrocarbon deposits on Titan. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009je003369] [Citation(s) in RCA: 134] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Plessis S, Carrasco N, Pernot P. Knowledge-based probabilistic representations of branching ratios in chemical networks: the case of dissociative recombinations. J Chem Phys 2010; 133:134110. [PMID: 20942526 DOI: 10.1063/1.3479907] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Experimental data about branching ratios for the products of dissociative recombination of polyatomic ions are presently the unique information source available to modelers of natural or laboratory chemical plasmas. Yet, because of limitations in the measurement techniques, data for many ions are incomplete. In particular, the repartition of hydrogen atoms among the fragments of hydrocarbons ions is often not available. A consequence is that proper implementation of dissociative recombination processes in chemical models is difficult, and many models ignore invaluable data. We propose a novel probabilistic approach based on Dirichlet-type distributions, enabling modelers to fully account for the available information. As an application, we consider the production rate of radicals through dissociative recombination in an ionospheric chemistry model of Titan, the largest moon of Saturn. We show how the complete scheme of dissociative recombination products derived with our method dramatically affects these rates in comparison with the simplistic H-loss mechanism implemented by default in all recent models.
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Affiliation(s)
- Sylvain Plessis
- Laboratoire de Chimie Physique, Univ Paris-Sud, UMR 8000, Orsay F-91405, France
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41
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Formation of nitrogenated organic aerosols in the Titan upper atmosphere. Proc Natl Acad Sci U S A 2010; 107:12423-8. [PMID: 20616074 DOI: 10.1073/pnas.0913353107] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many aspects of the nitrogen fixation process by photochemistry in the Titan atmosphere are not fully understood. The recent Cassini mission revealed organic aerosol formation in the upper atmosphere of Titan. It is not clear, however, how much and by what mechanism nitrogen is incorporated in Titan's organic aerosols. Using tunable synchrotron radiation at the Advanced Light Source, we demonstrate the first evidence of nitrogenated organic aerosol production by extreme ultraviolet-vacuum ultraviolet irradiation of a N(2)/CH(4) gas mixture. The ultrahigh-mass-resolution study with laser desorption ionization-Fourier transform-ion cyclotron resonance mass spectrometry of N(2)/CH(4) photolytic solid products at 60 and 82.5 nm indicates the predominance of highly nitrogenated compounds. The distinct nitrogen incorporations at the elemental abundances of H(2)C(2)N and HCN, respectively, are suggestive of important roles of H(2)C(2)N/HCCN and HCN/CN in their formation. The efficient formation of unsaturated hydrocarbons is observed in the gas phase without abundant nitrogenated neutrals at 60 nm, and this is confirmed by separately using (13)C and (15)N isotopically labeled initial gas mixtures. These observations strongly suggest a heterogeneous incorporation mechanism via short lived nitrogenated reactive species, such as HCCN radical, for nitrogenated organic aerosol formation, and imply that substantial amounts of nitrogen is fixed as organic macromolecular aerosols in Titan's atmosphere.
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Faure A, Vuitton V, Thissen R, Wiesenfeld L, Dutuit O. Fast ion–molecule reactions in planetary atmospheres: a semiempirical capture approach. Faraday Discuss 2010; 147:337-48; discussion 379-403. [DOI: 10.1039/c003908j] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Faure A, Vuitton V, Thissen R, Wiesenfeld L. A Semiempirical Capture Model for Fast Neutral Reactions at Low Temperature. J Phys Chem A 2009; 113:13694-9. [DOI: 10.1021/jp905609x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alexandre Faure
- Laboratoire de Planétologie, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5109, B.P. 53, 38041 Grenoble Cedex 09, France, and Laboratoire d’Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5571, B.P. 53, 38041 Grenoble Cedex 09, France
| | - Véronique Vuitton
- Laboratoire de Planétologie, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5109, B.P. 53, 38041 Grenoble Cedex 09, France, and Laboratoire d’Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5571, B.P. 53, 38041 Grenoble Cedex 09, France
| | - Roland Thissen
- Laboratoire de Planétologie, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5109, B.P. 53, 38041 Grenoble Cedex 09, France, and Laboratoire d’Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5571, B.P. 53, 38041 Grenoble Cedex 09, France
| | - Laurent Wiesenfeld
- Laboratoire de Planétologie, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5109, B.P. 53, 38041 Grenoble Cedex 09, France, and Laboratoire d’Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, CNRS UMR5571, B.P. 53, 38041 Grenoble Cedex 09, France
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Chemical dynamics of triacetylene formation and implications to the synthesis of polyynes in Titan's atmosphere. Proc Natl Acad Sci U S A 2009; 106:16078-83. [PMID: 19805262 DOI: 10.1073/pnas.0900525106] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
For the last four decades, the role of polyynes such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH) in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an UV radiation shield in planetary environments; thus, acting as prebiotic ozone, and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes that initiate the formation and control the growth of polyynes have been the least understood to date. Here, we present a combined experimental, theoretical, and modeling study on the synthesis of the polyyne triacetylene (HCCCCCCH) via the bimolecular gas phase reaction of the ethynyl radical (CCH) with diacetylene (HCCCCH). This elementary reaction is rapid, has no entrance barrier, and yields the triacetylene molecule via indirect scattering dynamics through complex formation in a single collision event. Photochemical models of Titan's atmosphere imply that triacetylene may serve as a building block to synthesize even more complex polyynes such as tetraacetylene (HCCCCCCCCH).
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Balucani N. Elementary reactions and their role in gas-phase prebiotic chemistry. Int J Mol Sci 2009; 10:2304-2335. [PMID: 19564951 PMCID: PMC2695279 DOI: 10.3390/ijms10052304] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2009] [Revised: 05/13/2009] [Accepted: 05/15/2009] [Indexed: 11/23/2022] Open
Abstract
The formation of complex organic molecules in a reactor filled with gaseous mixtures possibly reproducing the primitive terrestrial atmosphere and ocean demonstrated more than 50 years ago that inorganic synthesis of prebiotic molecules is possible, provided that some form of energy is provided to the system. After that groundbreaking experiment, gas-phase prebiotic molecules have been observed in a wide variety of extraterrestrial objects (including interstellar clouds, comets and planetary atmospheres) where the physical conditions vary widely. A thorough characterization of the chemical evolution of those objects relies on a multi-disciplinary approach: 1) observations allow us to identify the molecules and their number densities as they are nowadays; 2) the chemistry which lies behind their formation starting from atoms and simple molecules is accounted for by complex reaction networks; 3) for a realistic modeling of such networks, a number of experimental parameters are needed and, therefore, the relevant molecular processes should be fully characterized in laboratory experiments. A survey of the available literature reveals, however, that much information is still lacking if it is true that only a small percentage of the elementary reactions considered in the models have been characterized in laboratory experiments. New experimental approaches to characterize the relevant elementary reactions in laboratory are presented and the implications of the results are discussed.
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Affiliation(s)
- Nadia Balucani
- Dipartimento di Chimica, Università degli Studi di Perugia, 06123 Perugia, Italy; E-Mail:
; Tel. +39-075-585-5513; Fax: +39-075-585-5606
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Johnson RE. Sputtering and heating of Titan's upper atmosphere. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:753-771. [PMID: 19073463 DOI: 10.1098/rsta.2008.0244] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Titan is an important endpoint for understanding atmospheric evolution. Prior to Cassini's arrival at Saturn, modelling based on Voyager data indicated that the hydrogen escape rate was large (1-3x1028amus-1), but the escape rates for carbon and nitrogen species were relatively small (5x1026amus-1) and dominated by atmospheric sputtering. Recent analysis of the structure of Titan's thermosphere and corona attained from the Ion and Neutral Mass Spectrometer and the Huygens Atmospheric Structure Instrument on Cassini have led to substantially larger estimates of the loss rate for heavy species (0.3-5x1028amus-1). At the largest rate suggested, a mass that is a significant fraction of the present atmosphere would have been lost to space in 4Gyr; hence, understanding the nature of the processes driving escape is critical. The recent estimates of neutral escape are reviewed here, with particular emphasis on plasma-induced sputtering and heating. Whereas the loss of hydrogen is clearly indicated by the altitude dependence of the H2 density, three different one-dimensional models were used to estimate the heavy-molecule loss rate using the Cassini data for atmospheric density versus altitude. The solar heating rate and the nitrogen density profile versus altitude were used in a fluid dynamic model to extract an average net upward flux below the exobase; the diffusion of methane through nitrogen was described below the exobase using a model that allowed for outward flow; and the coronal structure above the exobase was simulated by presuming that the observed atmospheric structure was due to solar- and plasma-induced hot particle production. In the latter, it was hypothesized that hot recoils from photochemistry or plasma-ion-induced heating were required. In the other two models, the upward flow extracted is driven by heat conduction from below, which is assumed to continue to act above the nominal exobase, producing a process referred to as 'slow hydrodynamic' escape. These models and the resulting loss rates are reviewed and compared. It is pointed out that preliminary estimates of the composition of the magnetospheric plasma at Titan's orbit appear to be inconsistent with the largest loss rates suggested for the heavy species, and the mean upward flow extracted in the one-dimensional models could be consistent with atmospheric loss by other mechanisms or with transport to other regions of Titan's atmosphere.
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Affiliation(s)
- Robert E Johnson
- University of Virginia, Charlottesville, VA 22904, USA Department of Physics, New York University, New York, NY 10003, USA.
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Vuitton V, Yelle RV, Lavvas P. Composition and chemistry of Titan's thermosphere and ionosphere. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:729-741. [PMID: 19019780 DOI: 10.1098/rsta.2008.0233] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Titan has long been known to harbour the richest atmospheric chemistry in the Solar System. Until recently, it had been believed that complex hydrocarbons and nitriles were produced through neutral chemistry that would eventually lead to the formation of micrometre sized organic aerosols. However, recent measurements by the Cassini spacecraft are drastically changing our understanding of Titan's chemistry. The Ion and Neutral Mass Spectrometer (INMS) and the Cassini Plasma Spectrometer (CAPS) revealed an extraordinary complex ionospheric composition. INMS detected roughly 50 positive ions with m/z<100 and a density higher than 0.1cm-3. CAPS provided evidence for heavy (up to 350amu) positively and negatively charged (up to 4000amu) ions. These observations all indicate that Titan's ionospheric chemistry is incredibly complex and that molecular growth starts in the upper atmosphere rather than at lower altitude. Here, we review the recent progress made on ionospheric chemistry. The presence of heavy neutrals in the upper atmosphere has been inferred as a direct consequence of the presence of complex positive ions. Benzene (C6H6) is created by ion chemistry at high altitudes and its main photolysis product, the phenyl radical (C6H5), is at the origin of the formation of aromatic species at lower altitude.
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Affiliation(s)
- V Vuitton
- Laboratoire de Planétologie de Grenoble, CNRS, 38041 Grenoble, France Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0092, USA.
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Teanby NA, Irwin PGJ, de Kok R, Nixon CA. Dynamical implications of seasonal and spatial variations in Titan's stratospheric composition. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:697-711. [PMID: 19019781 DOI: 10.1098/rsta.2008.0164] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Titan's diverse inventory of photochemically produced gases can be used as tracers to probe atmospheric circulation. Since the arrival of the Cassini-Huygens mission in July 2004 it has been possible to map the seasonal and spatial variations of these compounds in great detail. Here, we use 3.5 years of data measured by the Cassini Composite InfraRed Spectrometer instrument to determine spatial and seasonal composition trends, thus providing clues to underlying atmospheric motions. Titan's North Pole (currently in winter) displays enrichment of trace species, implying subsidence is occurring there. This is consistent with the descending branch of a single south-to-north stratospheric circulation cell and a polar vortex. Lack of enrichment in the south over most of the observed time period argues against the presence of any secondary circulation cell in the Southern Polar stratosphere. However, a residual cap of enriched gas was observed over the South Pole early in the mission, which has since completely dissipated. This cap was most probably due to residual build-up from southern winter. These observations provide new and important constraints for models of atmospheric photochemistry and circulation.
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Affiliation(s)
- Nicholas A Teanby
- Atmospheric, Oceanic & Planetary Physics, Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK.
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Coates AJ. Interaction of Titan's ionosphere with Saturn's magnetosphere. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:773-788. [PMID: 19073464 DOI: 10.1098/rsta.2008.0248] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Titan is the only Moon in the Solar System with a significant permanent atmosphere. Within this nitrogen-methane atmosphere, an ionosphere forms. Titan has no significant magnetic dipole moment, and is usually located inside Saturn's magnetosphere. Atmospheric particles are ionized both by sunlight and by particles from Saturn's magnetosphere, mainly electrons, which reach the top of the atmosphere. So far, the Cassini spacecraft has made over 45 close flybys of Titan, allowing measurements in the ionosphere and the surrounding magnetosphere under different conditions. Here we review how Titan's ionosphere and Saturn's magnetosphere interact, using measurements from Cassini low-energy particle detectors. In particular, we discuss ionization processes and ionospheric photoelectrons, including their effect on ion escape from the ionosphere. We also discuss one of the unexpected discoveries in Titan's ionosphere, the existence of extremely heavy negative ions up to 10000amu at 950km altitude.
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Affiliation(s)
- Andrew J Coates
- Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT, UK.
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Bézard B. Composition and chemistry of Titan's stratosphere. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:683-695. [PMID: 19019784 DOI: 10.1098/rsta.2008.0186] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Our present knowledge of the composition and chemistry of Titan's stratosphere is reviewed. Thermal measurements by the Cassini spacecraft show that the mixing ratios of all photochemical species, except ethylene, increase with altitude at equatorial and southern latitudes, reflecting transport from a high-altitude source to a condensation sink in the lower stratosphere. Most compounds are enriched at latitudes northward of 45 degrees N, a consequence of subsidence in the winter polar vortex. This enrichment is much stronger for nitriles and complex hydrocarbons than for ethane and acetylene. Titan's chemistry originates from breakdown of methane due to photodissociation in the upper atmosphere and catalytical reactions in the stratosphere, and from destruction of nitrogen both by UV photons and electrons. Photochemistry also produces haze particles made of complex refractory material, albeit at a lower rate than ethane, the most abundant gas product. Haze characteristics (vertical distribution, physical and spectral properties) inferred by several instruments aboard Cassini/Huygens are discussed here.
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Affiliation(s)
- Bruno Bézard
- LESIA, Observatoire de Paris, CNRS, 92195 Meudon, France.
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