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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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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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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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Cui J, Yelle RV, Strobel DF, Müller-Wodarg ICF, Snowden DS, Koskinen TT, Galand M. The CH4structure in Titan's upper atmosphere revisited. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012je004222] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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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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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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Westlake JH, Bell JM, Waite JH, Johnson RE, Luhmann JG, Mandt KE, Magee BA, Rymer AM. Titan's thermospheric response to various plasma environments. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016251] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. H. Westlake
- Department of Physics and Astronomy; University of Texas at San Antonio; San Antonio Texas USA
| | - J. M. Bell
- 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
| | - R. E. Johnson
- Engineering Physics Program; University of Virginia; Charlottesville Virginia USA
| | - J. G. Luhmann
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - K. E. Mandt
- Space Science and Engineering Division; Southwest Research Institute; San Antonio Texas USA
- Department of Environmental and Civil Engineering; University of Texas at San Antonio; San Antonio Texas USA
| | - B. A. Magee
- Space Science and Engineering Division; Southwest Research Institute; San Antonio Texas USA
| | - A. M. Rymer
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
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Yelle RV, Vuitton V, Lavvas P, Klippenstein SJ, Smith MA, Hörst SM, Cui J. Formation of NH3 and CH2NH in Titan's upper atmosphere. Faraday Discuss 2011; 147:31-49; discussion 83-102. [PMID: 21302541 DOI: 10.1039/c004787m] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The large abundance of NH3 in Titan's upper atmosphere is a consequence of coupled ion and neutral chemistry. The density of NH3 is inferred from the measured abundance of NH4+. NH3 is produced primarily through reaction of NH2 with H2CN, a process neglected in previous models. NH2 is produced by several reactions including electron recombination of CH2NH2+. The density of CH2NH2+ is closely linked to the density of CH2NH through proton exchange reactions and recombination. CH2NH is produced by reaction of N(2D) and NH with ambient hydrocarbons. Thus, production of NH3 is the result of a chain of reactions involving non-nitrile functional groups and the large density of NH3 implies large densities for these associated molecules. This suggests that amine and imine functional groups may be incorporated as well in other, more complex organic molecules.
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Affiliation(s)
- Roger V Yelle
- Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721, 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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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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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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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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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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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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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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Cui J, Yelle RV, Volk K. Distribution and escape of molecular hydrogen in Titan's thermosphere and exosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007je003032] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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