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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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Shebanits O, Vigren E, Wahlund JE, Edberg NJT, Cui J, Mandt KE, Waite JH. Photoionization Modeling of Titan's Dayside Ionosphere. THE ASTROPHYSICAL JOURNAL. LETTERS 2017; 850:L26. [PMID: 31105929 PMCID: PMC6525073 DOI: 10.3847/2041-8213/aa998d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Previous modeling studies of Titan's dayside ionosphere predict electron number densities that are roughly a factor of 2 higher than those observed by the RPWS/Langmuir probe. The issue can equivalently be described as the ratio between the calculated electron production rates and the square of the observed electron number densities resulting in roughly a factor of 4 higher effective recombination coefficient than expected from the ion composition and the electron temperature. Here we make an extended reassessment of Titan's dayside ionization balance, focusing on 34 flybys between TA and T120. Using a recalibrated data set and by taking the presence of negative ions into account, we arrive at lower effective recombination coefficients compared with earlier studies. The values are still higher than expected from the ion composition and the electron temperature, but by a factor of ~2-3 instead of a factor of ~4. We have also investigated whether the derived effective recombination coefficients display dependencies on the solar zenith angle (SZA), the integrated solar EUV intensity (<80 nm), and the corotational plasma ram direction (RAM), and found statistically significant trends, which may be explained by a declining photoionization against the background ionization by magnetospheric particles (trends in SZA and RAM) and altered photochemistry (trend in EUV). We find that a series of flybys that occurred during solar minimum (2008) and with similar flyby geometries are associated with enhanced values of the effective recombination coefficient compared with the remaining data set, which also suggests a chemistry dependence on the sunlight conditions.
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Affiliation(s)
- O Shebanits
- Swedish Institute of Space Physics, Uppsala, Sweden
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - E Vigren
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - J-E Wahlund
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - N J T Edberg
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - J Cui
- School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai, Guangdong, China
| | - K E Mandt
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
| | - J H Waite
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
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3
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Shebanits O, Vigren E, Wahlund JE, Holmberg MKG, Morooka M, Edberg NJT, Mandt KE, Waite JH. Titan's ionosphere: A survey of solar EUV influences. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2017; 122:7491-7503. [PMID: 31106105 PMCID: PMC6525010 DOI: 10.1002/2017ja023987] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Effects of solar EUV on positive ions and heavy negative charge carriers (molecular ions, aerosol, and/or dust) in Titan's ionosphere are studied over the course of almost 12 years, including 78 flybys below 1400 km altitude between TA (October 2004) and T120 (June 2016). The Radio and Plasma Wave Science/Langmuir Probe-measured ion charge densities (normalized by the solar zenith angle) show statistically significant variations with respect to the solar EUV flux. Dayside charge densities increase by a factor of ≈2 from solar minimum to maximum, while nightside charge densities are found to anticorrelate with the EUV flux and decrease by a factor of ≈3-4. The overall EUV dependence of the ion charge densities suggest inapplicability of the idealized Chapman theory below 1200 km in Titan's ionosphere. Nightside charge densities are also found to vary along Titan's orbit, with higher values in the sunward magnetosphere of Saturn compared to the magnetotail.
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Affiliation(s)
- O. Shebanits
- Swedish Institute of Space Physics, Uppsala, Sweden
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - E. Vigren
- Swedish Institute of Space Physics, Uppsala, Sweden
| | | | - M. K. G. Holmberg
- Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
- CNRS, IRAP, Toulouse, France
| | - M. Morooka
- Swedish Institute of Space Physics, Uppsala, Sweden
| | | | - K. E. Mandt
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
| | - J. H. Waite
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
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4
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Shebanits O, Wahlund JE, Edberg NJT, Crary FJ, Wellbrock A, Andrews DJ, Vigren E, Desai RT, Coates AJ, Mandt KE, Waite JH. Ion and aerosol precursor densities in Titan's ionosphere: A multi-instrument case study. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2016; 121:10075-10090. [PMID: 31106104 PMCID: PMC6525009 DOI: 10.1002/2016ja022980] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The importance of the heavy ions and dust grains for the chemistry and aerosol formation in Titan's ionosphere has been well established in the recent years of the Cassini mission. In this study we combine independent in situ plasma (Radio Plasma and Wave Science Langmuir Probe (RPWS/LP)) and particle (Cassini Plasma Science Electron Spectrometer, Cassini Plasma Science Ion Beam Spectrometer, and Ion and Neutral Mass Spectrometer) measurements of Titan's ionosphere for selected flybys (T16, T29, T40, and T56) to produce altitude profiles of mean ion masses including heavy ions and develop a Titan-specific method for detailed analysis of the RPWS/LP measurements (applicable to all flybys) to further constrain ion charge densities and produce the first empirical estimate of the average charge of negative ions and/or dust grains. Our results reveal the presence of an ion-ion (dusty) plasma below ~1100 km altitude, with charge densities exceeding the primary ionization peak densities by a factor ≥2 in the terminator and nightside ionosphere (n e /n i ≤ 0.1). We suggest that ion-ion (dusty) plasma may also be present in the dayside ionosphere below 900 km (n e /n i < 0.5 at 1000 km altitude). The average charge of the dust grains (≥1000 amu) is estimated to be between -2.5 and -1.5 elementary charges, increasing toward lower altitudes.
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Affiliation(s)
- O. Shebanits
- Swedish Institute of Space Physics, Uppsala, Sweden
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | | | | | - F. J. Crary
- University of Colorado Boulder, Boulder, Colorado, USA
| | - A. Wellbrock
- Mullard Space Science Laboratory, University College London, London, UK
- Centre for Planetary Sciences, University College London/Birkbeck, London, UK
| | | | - E. Vigren
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - R. T. Desai
- Mullard Space Science Laboratory, University College London, London, UK
- Centre for Planetary Sciences, University College London/Birkbeck, London, UK
| | - A. J. Coates
- Mullard Space Science Laboratory, University College London, London, UK
- Centre for Planetary Sciences, University College London/Birkbeck, London, UK
| | - K. E. Mandt
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
| | - J. H. Waite
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
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Coates AJ, Wellbrock A, Waite JH, Jones GH. A new upper limit to the field-aligned potential near Titan. GEOPHYSICAL RESEARCH LETTERS 2015; 42:4676-4684. [PMID: 27609997 PMCID: PMC4994318 DOI: 10.1002/2015gl064474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Accepted: 05/22/2015] [Indexed: 06/06/2023]
Abstract
Neutral particles dominate regions of the Saturn magnetosphere and locations near several of Saturn's moons. Sunlight ionizes neutrals, producing photoelectrons with characteristic energy spectra. The Cassini plasma spectrometer electron spectrometer has detected photoelectrons throughout these regions, where photoelectrons may be used as tracers of magnetic field morphology. They also enhance plasma escape by setting up an ambipolar electric field, since the relatively energetic electrons move easily along the magnetic field. A similar mechanism is seen in the Earth's polar wind and at Mars and Venus. Here we present a new analysis of Titan photoelectron data, comparing spectra measured in the sunlit ionosphere at ~1.4 Titan radii (RT) and at up to 6.8 RT away. This results in an upper limit on the potential of 2.95 V along magnetic field lines associated with Titan at up to 6.8 RT, which is comparable to some similar estimates for photoelectrons seen in Earth's magnetosphere.
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Affiliation(s)
- Andrew J Coates
- Mullard Space Science Laboratory University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK
| | - Anne Wellbrock
- Mullard Space Science Laboratory University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK
| | | | - Geraint H Jones
- Mullard Space Science Laboratory University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK
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Mandt KE, Gell DA, Perry M, Hunter Waite J, Crary FA, Young D, Magee BA, Westlake JH, Cravens T, Kasprzak W, Miller G, Wahlund JE, Ågren K, Edberg NJT, Heays AN, Lewis BR, Gibson ST, de la Haye V, Liang MC. Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012je004139] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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7
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Garnier P, Wahlund JE, Holmberg MKG, Morooka M, Grimald S, Eriksson A, Schippers P, Gurnett DA, Krimigis SM, Krupp N, Coates A, Crary F, Gustafsson G. The detection of energetic electrons with the Cassini Langmuir probe at Saturn. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011ja017298] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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8
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Kliore AJ, Nagy AF, Cravens TE, Richard MS, Rymer AM. Unusual electron density profiles observed by Cassini radio occultations in Titan's ionosphere: Effects of enhanced magnetospheric electron precipitation? ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja016694] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- A. J. Kliore
- Jet Propulsion Laboratory; California Institute of Technology; Pasadena California USA
| | - A. F. Nagy
- Department of Atmospheric, Oceanic and Space Science; University of Michigan; Ann Arbor Michigan USA
| | - T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - M. S. Richard
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - A. M. Rymer
- Applied Physics Laboratory; John Hopkins University; Laurel Maryland USA
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9
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Richard MS, Cravens TE, Robertson IP, Waite JH, Wahlund JE, Crary FJ, Coates AJ. Energetics of Titan's ionosphere: Model comparisons with Cassini data. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja016603] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- M. S. Richard
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - I. P. Robertson
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - J. H. Waite
- Southwest Research Institute; San Antonio Texas USA
| | | | - F. J. Crary
- Southwest Research Institute; San Antonio Texas USA
| | - A. J. Coates
- Mullard Space Science Laboratory, Holmbury St. Mary; University College London; Dorking, Surrey UK
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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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11
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Ågren K, Andrews DJ, Buchert SC, Coates AJ, Cowley SWH, Dougherty MK, Edberg NJT, Garnier P, Lewis GR, Modolo R, Opgenoorth H, Provan G, Rosenqvist L, Talboys DL, Wahlund JE, Wellbrock A. Detection of currents and associated electric fields in Titan's ionosphere from Cassini data. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016100] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- K. Ågren
- Swedish Institute of Space Physics; Uppsala Sweden
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - D. J. Andrews
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | | | | | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | | | | | | | - G. R. Lewis
- Mullard Space Science Laboratory; Dorking UK
| | - R. Modolo
- UVSQ/LATMOS-IPSL/CNRS-INSU; Guyancourt France
| | | | - G. Provan
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | | | - D. L. Talboys
- Department of Physics and Astronomy; University of Leicester; Leicester UK
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12
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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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13
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Wei HY, Russell CT, Dougherty MK, Neubauer FM, Ma YJ. Upper limits on Titan's magnetic moment and implications for its interior. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009je003538] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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14
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Cravens TE, Richard M, Ma YJ, Bertucci C, Luhmann JG, Ledvina S, Robertson IP, Wahlund JE, Ågren K, Cui J, Muller-Wodarg I, Waite JH, Dougherty M, Bell J, Ulusen D. Dynamical and magnetic field time constants for Titan's ionosphere: Empirical estimates and comparisons with Venus. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja015050] [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]
Affiliation(s)
- T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - M. Richard
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - Y.-J. Ma
- Institute of Geophysics and Planetary Physics; University of California; Los Angeles California USA
| | - C. Bertucci
- Instituto de Astronomía y Física del Espacio; Buenos Aires Argentina
| | - J. G. Luhmann
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - S. Ledvina
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - I. P. Robertson
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | | | - K. Ågren
- Swedish Institute of Space Physics; Uppsala Sweden
| | - J. Cui
- Space and Atmospheric Physics Group, Blackett Laboratory; Imperial College London; London UK
| | - I. Muller-Wodarg
- Space and Atmospheric Physics Group, Blackett Laboratory; Imperial College London; London UK
| | - J. H. Waite
- Southwest Research Institute; San Antonio Texas USA
| | - M. Dougherty
- Space and Atmospheric Physics Group, Blackett Laboratory; Imperial College London; London UK
| | - J. Bell
- Southwest Research Institute; San Antonio Texas USA
| | - D. Ulusen
- Space Sciences Laboratory; University of California; Berkeley California USA
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15
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Galand M, Yelle R, Cui J, Wahlund JE, Vuitton V, Wellbrock A, Coates A. Ionization sources in Titan's deep ionosphere. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja015100] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Marina Galand
- Department of Physics; Imperial College London; London UK
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Roger Yelle
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
| | - Jun Cui
- Department of Physics; Imperial College London; London UK
| | | | - Véronique Vuitton
- Laboratoire de Planétologie de Grenoble; Université Joseph Fourier; Grenoble France
| | - Anne Wellbrock
- Mullard Space Science Laboratory; University College London; Surrey UK
| | - Andrew Coates
- Mullard Space Science Laboratory; University College London; Surrey UK
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16
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Cui J, Galand M, Yelle RV, Wahlund JE, Ågren K, Waite JH, Dougherty MK. Ion transport in Titan's upper atmosphere. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja014563] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. Cui
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
| | - M. Galand
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
| | - R. V. Yelle
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
| | | | - K. Ågren
- Swedish Institute of Space Physics; Uppsala Sweden
| | - J. H. Waite
- Southwest Research Institute; San Antonio Texas USA
| | - M. K. Dougherty
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
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17
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Adams NG, Mathews LD, Osborne, Jr D. Laboratory chemistry relevant to understanding and modeling the ionosphere of Titan. Faraday Discuss 2010; 147:323-35; discussion 379-403. [DOI: 10.1039/c003233f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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18
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Coates AJ, Wellbrock A, Lewis GR, Jones GH, Young DT, Crary FJ, Waite JH, Johnson RE, Hill TW, Sittler Jr. EC. Negative ions at Titan and Enceladus: recent results. Faraday Discuss 2010; 147:293-305; discussion 379-403. [DOI: 10.1039/c004700g] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Li Y, Liu HL, Sun YB, Li Z, Huang XR, Sun CC. Theoretical study on the ion–molecule reaction of HCN+ with NH3. Theor Chem Acc 2009. [DOI: 10.1007/s00214-009-0631-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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20
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Cui J, Galand M, Yelle RV, Vuitton V, Wahlund JE, Lavvas PP, Müller-Wodarg ICF, Cravens TE, Kasprzak WT, Waite JH. Diurnal variations of Titan's ionosphere. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2009ja014228] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. Cui
- Space and Atmospheric Physics Group, Department of Physics; Imperial College; London UK
| | - M. Galand
- Space and Atmospheric Physics Group, Department of Physics; Imperial College; London UK
| | - R. V. Yelle
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
| | - V. Vuitton
- Laboratoire de Planétologie de Grenoble; Université Joseph Fourier/CNRS; Grenoble France
| | - J.-E. Wahlund
- Uppsala Division; Swedish Institute of Space Physics; Uppsala Sweden
| | - P. P. Lavvas
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
| | | | - T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - W. T. Kasprzak
- Solar System Exploration Division; NASA Goddard Space Flight Center; Greenbelt Maryland USA
| | - J. H. Waite
- Space Science and Engineering Division; Southwest Research Institute; San Antonio Texas USA
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21
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Winglee RM, Snowden D, Kidder A. Modification of Titan's ion tail and the Kronian magnetosphere: Coupled magnetospheric simulations. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008ja013343] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- R. M. Winglee
- Department of Earth and Space Science; University of Washington; Seattle Washington USA
| | - D. Snowden
- Department of Earth and Space Science; University of Washington; Seattle Washington USA
| | - A. Kidder
- Department of Earth and Space Science; University of Washington; Seattle Washington USA
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22
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Ma YJ, Russell CT, Nagy AF, Toth G, Bertucci C, Dougherty MK, Neubauer FM, Wellbrock A, Coates AJ, Garnier P, Wahlund JE, Cravens TE, Crary FJ. Time-dependent global MHD simulations of Cassini T32 flyby: From magnetosphere to magnetosheath. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008ja013676] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Y. J. Ma
- Institute of Geophysics and Planetary Physics; University of California Los Angeles; Los Angeles California USA
| | - C. T. Russell
- Institute of Geophysics and Planetary Physics; University of California Los Angeles; Los Angeles California USA
| | - A. F. Nagy
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - G. Toth
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - C. Bertucci
- Blackett Laboratory, Space and Atmospheric Physics Group; Imperial College London; London UK
| | - M. K. Dougherty
- Blackett Laboratory, Space and Atmospheric Physics Group; Imperial College London; London UK
| | - F. M. Neubauer
- Institute of Geophysics and Meteorology; University of Cologne; Cologne Germany
| | - A. Wellbrock
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; London UK
| | - A. J. Coates
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; London UK
| | - P. Garnier
- Swedish Institute of Space Physics; Uppsala Sweden
| | | | - T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - F. J. Crary
- Southwest Research Institute; San Antonio Texas USA
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23
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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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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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Hanford AD, Long LN. The direct simulation of acoustics on Earth, Mars, and Titan. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2009; 125:640-650. [PMID: 19206842 DOI: 10.1121/1.3050279] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
With the recent success of the Huygens lander on Titan, a moon of Saturn, there has been renewed interest in further exploring the acoustic environments of the other planets in the solar system. The direct simulation Monte Carlo (DSMC) method is used here for modeling sound propagation in the atmospheres of Earth, Mars, and Titan at a variety of altitudes above the surface. DSMC is a particle method that describes gas dynamics through direct physical modeling of particle motions and collisions. The validity of DSMC for the entire range of Knudsen numbers (Kn), where Kn is defined as the mean free path divided by the wavelength, allows for the exploration of sound propagation in planetary environments for all values of Kn. DSMC results at a variety of altitudes on Earth, Mars, and Titan including the details of nonlinearity, absorption, dispersion, and molecular relaxation in gas mixtures are given for a wide range of Kn showing agreement with various continuum theories at low Kn and deviation from continuum theory at high Kn. Despite large computation time and memory requirements, DSMC is the method best suited to study high altitude effects or where continuum theory is not valid.
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Affiliation(s)
- Amanda D Hanford
- Applied Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16804, USA.
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De La Haye V, Waite JH, Cravens TE, Bougher SW, Robertson IP, Bell JM. Heating Titan's upper atmosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013078] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
| | - J. H. Waite
- Southwest Research Institute; San Antonio Texas USA
| | - T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - S. W. Bougher
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - I. P. Robertson
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - J. M. Bell
- Southwest Research Institute; San Antonio Texas USA
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Achilleos N, Arridge CS, Bertucci C, Jackman CM, Dougherty MK, Khurana KK, Russell CT. Large-scale dynamics of Saturn's magnetopause: Observations by Cassini. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013265] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- N. Achilleos
- Atmospheric Physics Laboratory, Center for Planetary Sciences; University College London; London UK
- Blackett Laboratory; Imperial College London; London UK
| | - C. S. Arridge
- Blackett Laboratory; Imperial College London; London UK
- Mullard Space Science Laboratory, Center for Planetary Sciences; University College London, Holmbury St Mary; London UK
| | - C. Bertucci
- Blackett Laboratory; Imperial College London; London UK
| | - C. M. Jackman
- Blackett Laboratory; Imperial College London; London UK
| | | | - K. K. Khurana
- Institute of Geophysics and Planetary Physics; University of California-Los Angeles; Los Angeles California USA
| | - C. T. Russell
- Institute of Geophysics and Planetary Physics; University of California-Los Angeles; Los Angeles California USA
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Li Y, Liu HL, Huang XR, Wang D, Sun CC, Tang AC. Reaction Mechanism of HCN+ + C2H4: A Theoretical Study. J Phys Chem A 2008; 112:12252-62. [DOI: 10.1021/jp805285p] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Yan Li
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China
| | - Hui-ling Liu
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China
| | - Xu-ri Huang
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China
| | - Dequan Wang
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China
| | - Chia-chung Sun
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China
| | - Au-chin Tang
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China
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Garnier P, Dandouras I, Toublanc D, Roelof EC, Brandt PC, Mitchell DG, Krimigis SM, Krupp N, Hamilton DC, Dutuit O, Wahlund JE. The lower exosphere of Titan: Energetic neutral atoms absorption and imaging. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013029] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- P. Garnier
- Centre d'Etude Spatiale des Rayonnements; CNRS/Paul Sabatier University; Toulouse France
- Swedish Institute of Space Physics; Uppsala Sweden
| | - I. Dandouras
- Centre d'Etude Spatiale des Rayonnements; CNRS/Paul Sabatier University; Toulouse France
| | - D. Toublanc
- Centre d'Etude Spatiale des Rayonnements; CNRS/Paul Sabatier University; Toulouse France
| | - E. C. Roelof
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - P. C. Brandt
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - D. G. Mitchell
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - S. M. Krimigis
- Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
| | - N. Krupp
- Max-Planck-Institut fur Sonnensystemforschung; Lindau Germany
| | - D. C. Hamilton
- Department of Physics; University of Maryland; College Park Maryland USA
| | - O. Dutuit
- Laboratoire de Planetologie de Grenoble; Universite Joseph Fourier; Grenoble France
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30
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Kliore AJ, Nagy AF, Marouf EA, French RG, Flasar FM, Rappaport NJ, Anabttawi A, Asmar SW, Kahann DS, Barbinis E, Goltz GL, Fleischman DU, Rochblatt DJ. First results from the Cassini radio occultations of the Titan ionosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007ja012965] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Avydas J. Kliore
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Andrew F. Nagy
- Space Physics Research Laboratory, University of Michigan; Ann Arbor Michigan USA
| | - Essam A. Marouf
- Department of Electrical Engineering; San Jose State University; San Jose California USA
| | - Richard G. French
- Astronomy Department; Wellesley College; Wellesley Massachusetts USA
| | | | - Nicole J. Rappaport
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Aseel Anabttawi
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Sami W. Asmar
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Daniel S. Kahann
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Elias Barbinis
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Gene L. Goltz
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - Don U. Fleischman
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
| | - David J. Rochblatt
- Jet Propulsion Laboratory, California Institute of Technology; Pasadena California USA
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Bertucci C, Achilleos N, Dougherty MK, Modolo R, Coates AJ, Szego K, Masters A, Ma Y, Neubauer FM, Garnier P, Wahlund JE, Young DT. The Magnetic Memory of Titan's Ionized Atmosphere. Science 2008; 321:1475-8. [DOI: 10.1126/science.1159780] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- C. Bertucci
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - N. Achilleos
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - M. K. Dougherty
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - R. Modolo
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - A. J. Coates
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - K. Szego
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - A. Masters
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - Y. Ma
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - F. M. Neubauer
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - P. Garnier
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - J.-E. Wahlund
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
| | - D. T. Young
- Space and Atmospheric Physics Group, Imperial College London, The Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
- Centre for Planetary Sciences, University College London, UK
- Department of Physics and Astronomy, University of Iowa, 613 Van Allen Hall, Iowa City, IA 52242–1479, USA
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
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32
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Geppert W, Larsson M. Dissociative recombination in the interstellar medium and planetary ionospheres. Mol Phys 2008. [DOI: 10.1080/00268970802322074] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Li Y, Liu HL, Huang XR, Geng CY, Sun CC, Tang AC. Theoretical study of the reaction mechanism of HCN+ and CH4 of relevance to Titan's ion chemistry. J Phys Chem A 2008; 112:2693-701. [PMID: 18318514 DOI: 10.1021/jp710006b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Titan is the largest satellite of Saturn. In its atmosphere, CH4 is the most abundant neutral after nitrogen. In this paper, the complex doublet potential-energy surface related to the reaction between HCN+ and CH4 is investigated at the B3LYP/6-311G(d,p), CCSD(T)/6-311G++(3df,2pd)(single-point), and QCISD/6-311G(d,p) computational levels. A total of seven products are located on the PES. The initial association of HCN+ with CH4 is found to be a prereaction complex 1 (HCNHCH3(+)) without barrier. Starting from 1, the most feasible pathway is the direct H-abstraction process (the internal C-H bond dissociation) leading to the product P1 (HCNH++CH3). By C-C addition, prereaction complex 1 can form intermediate 2 (HNCHCH3(+)) and then lead to the product P2 (CH3CNH++H). The rate-controlling step of this process is only 25.6 kcal/mol. It makes the Path P2 (1) R --> 1 --> TS1/2 --> 2 --> TS2/P2 --> P2 another possible way for the reaction. P3 (HCNCH3(+) + H), P5 (cNCHCH2(+) + H2), and P6 (NCCH3(+) + H2) are exothermic products, but they have higher barriers (more than 40.0 kcal/mol); P4 (H + HCN + CH3(+)) and P7 (H + H2 + HCCNH+) are endothermic products. They should be discovered under different experimental or interstellar conditions. The present study may be helpful for investigating the analogous ion-molecule reaction in Titan's atmosphere.
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Affiliation(s)
- Yan Li
- State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China
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Modolo R, Chanteur GM. A global hybrid model for Titan's interaction with the Kronian plasma: Application to the Cassini Ta flyby. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007ja012453] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- R. Modolo
- Centre d'Etudes des Environnements Terrestre et Plantaires; Institut Pierre Simon Laplace; Vélizy France
- Swedish Institute of Space Physics; Uppsala Sweden
| | - G. M. Chanteur
- Centre d'Etudes des Environnements Terrestre et Plantaires; Institut Pierre Simon Laplace; Vélizy France
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35
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Snowden D, Winglee R, Bertucci C, Dougherty M. Three-dimensional multifluid simulation of the plasma interaction at Titan. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2007ja012393] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- D. Snowden
- Department of Earth and Space Sciences; University of Washington; Seattle Washington USA
| | - R. Winglee
- Department of Earth and Space Sciences; University of Washington; Seattle Washington USA
| | - C. Bertucci
- Space and Atmospheric Physics Group; Imperial College London UK
| | - M. Dougherty
- Space and Atmospheric Physics Group; Imperial College London UK
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36
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Yamauchi M, Wahlund JE. Role of the ionosphere for the atmospheric evolution of planets. ASTROBIOLOGY 2007; 7:783-800. [PMID: 17963477 DOI: 10.1089/ast.2007.0140] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We have synthesized current understanding, mainly observations, with regard to ion escape mechanisms to space from the ionosphere and exosphere of Titan and Earth-type planets, with the intent to provide an improved input for models of atmospheric evolution on early Earth and Earth-type planets and exoplanets. We focus on the role of the ionosphere and its non-linear response to solar parameters, all of which have been underestimated in current models of ancient atmospheric escape (4 billion years ago). Factors that have been overlooked include the following: (1) Much larger variation of O(+) outflow than H(+) outflow from the terrestrial ionosphere, depending on solar and geomagnetic activities (an important consideration when attempting to determine the oxidized state of the atmosphere of early Earth); (2) magnetization of the ionopause, which keeps ionospheric ions from escaping and controls many other escape processes; (3) extra ionization by, for example, the critical ionization velocity mechanism, which expands the ionosphere to greater altitudes than current models predict; and (4) the large escape of cold ions from the dense, expanded ionosphere of Titan. Here we offer, as a guideline for quantitative simulations, a qualitative diagnosis of increases or decreases of non-thermal escape related to the ionosphere for magnetized and unmagnetized planets in response to changes in solar parameters (i.e., solar EUV/FUV flux, solar wind dynamic pressure, and interplanetary magnetic field).
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Dóbé Z, Szego K, Quest KB, Shapiro VD, Hartle RE, Sittler EC. Nonlinear evolution of modified two-stream instability above ionosphere of Titan: Comparison with the data of the Cassini Plasma Spectrometer. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006ja011770] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Zoltán Dóbé
- Központi Fizikai Kutató Intézet Research Institute for Particle and Nuclear Physics; Budapest Hungary
| | - Karoly Szego
- Központi Fizikai Kutató Intézet Research Institute for Particle and Nuclear Physics; Budapest Hungary
| | - Kevin B. Quest
- Electrical and Computer Engineering Department; University of California San Diego; La Jolla California USA
| | - Vitali D. Shapiro
- Electrical and Computer Engineering Department; University of California San Diego; La Jolla California USA
| | - R. E. Hartle
- NASA Goddard Space Flight Center; Greenbelt Maryland USA
| | - E. C. Sittler
- NASA Goddard Space Flight Center; Greenbelt Maryland USA
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Neubauer FM, Backes H, Dougherty MK, Wennmacher A, Russell CT, Coates A, Young D, Achilleos N, André N, Arridge CS, Bertucci C, Jones GH, Khurana KK, Knetter T, Law A, Lewis GR, Saur J. Titan's near magnetotail from magnetic field and electron plasma observations and modeling: Cassini flybys TA, TB, and T3. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2006ja011676] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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39
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Ma Y, Nagy AF, Cravens TE, Sokolov IV, Hansen KC, Wahlund JE, Crary FJ, Coates AJ, Dougherty MK. Comparisons between MHD model calculations and observations of Cassini flybys of Titan. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005ja011481] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
The Cassini Orbiter spacecraft first skimmed through the tenuous upper atmosphere of Titan on 26 October 2004. This moon of Saturn is unique in our solar system, with a dense nitrogen atmosphere that is cold enough in places to rain methane, the feedstock for the atmospheric chemistry that produces hydrocarbons, nitrile compounds, and Titan's orange haze. The data returned from this flyby supply new information on the magnetic field and plasma environment around Titan, expose new facets of the dynamics and chemistry of Titan's atmosphere, and provide the first glimpses of what appears to be a complex, fluid-processed, geologically young Titan surface.
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Affiliation(s)
- Paul R Mahaffy
- Solar System Exploration Division, NASA, Goddard Space Flight Center, Greenbelt, MD 20771, USA.
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41
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Backes H, Neubauer FM, Dougherty MK, Achilleos N, André N, Arridge CS, Bertucci C, Jones GH, Khurana KK, Russell CT, Wennmacher A. Titan's Magnetic Field Signature During the First Cassini Encounter. Science 2005; 308:992-5. [PMID: 15890875 DOI: 10.1126/science.1109763] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The magnetic field signature obtained by Cassini during its first close encounter with Titan on 26 October 2004 is presented and explained in terms of an advanced model. Titan was inside the saturnian magnetosphere. A magnetic field minimum before closest approach marked Cassini's entry into the magnetic ionopause layer. Cassini then left the northern and entered the southern magnetic tail lobe. The magnetic field before and after the encounter was approximately constant for approximately 20 Titan radii, but the field orientation changed exactly at the location of Titan's orbit. No evidence of an internal magnetic field at Titan was detected.
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Affiliation(s)
- Heiko Backes
- Institut für Geophysik und Meteorologie, Universität zu Köln, Albertus Magnus Platz, 50678 Cologne, Germany.
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