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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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Abdelwahed HG, Mahmoud AA. Propagation of shock wave of nitrogen gas in Titan stratosphere. JOURNAL OF TAIBAH UNIVERSITY FOR SCIENCE 2021. [DOI: 10.1080/16583655.2021.1996134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- H. G. Abdelwahed
- College of Science and Humanitarian Studies, Physics Department, Prince Sattam Bin Abdul Aziz University, Alkharj, Kingdom of Saudi Arabia
- Theoretical Physics Research Group, Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt
| | - Abeer A. Mahmoud
- Theoretical Physics Research Group, Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt
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Gravity Waves in Planetary Atmospheres: Their Effects and Parameterization in Global Circulation Models. ATMOSPHERE 2019. [DOI: 10.3390/atmos10090531] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The dynamical and thermodynamical importance of gravity waves was initially recognized in the atmosphere of Earth. Extensive studies over recent decades demonstrated that gravity waves exist in atmospheres of other planets, similarly play a significant role in the vertical coupling of atmospheric layers and, thus, must be included in numerical general circulation models. Since the spatial scales of gravity waves are smaller than the typical spatial resolution of most models, atmospheric forcing produced by them must be parameterized. This paper presents a review of gravity waves in planetary atmospheres, outlines their main characteristics and forcing mechanisms, and summarizes approaches to capturing gravity wave effects in numerical models. The main goal of this review is to bridge research communities studying atmospheres of Earth and other planets.
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The formation and evolution of Titan's winter polar vortex. Nat Commun 2017; 8:1586. [PMID: 29162820 PMCID: PMC5698511 DOI: 10.1038/s41467-017-01839-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 10/18/2017] [Indexed: 11/09/2022] Open
Abstract
Saturn’s largest moon Titan has a substantial nitrogen-methane atmosphere, with strong seasonal effects, including formation of winter polar vortices. Following Titan’s 2009 northern spring equinox, peak solar heating moved to the northern hemisphere, initiating south-polar subsidence and winter polar vortex formation. Throughout 2010–2011, strengthening subsidence produced a mesospheric hot-spot and caused extreme enrichment of photochemically produced trace gases. However, in 2012 unexpected and rapid mesospheric cooling was observed. Here we show extreme trace gas enrichment within the polar vortex dramatically increases mesospheric long-wave radiative cooling efficiency, causing unusually cold temperatures 2–6 years post-equinox. The long time-frame to reach a stable vortex configuration results from the high infrared opacity of Titan’s trace gases and the relatively long atmospheric radiative time constant. Winter polar hot-spots have been observed on other planets, but detection of post-equinox cooling is so far unique to Titan. The polar hot-spot appeared in Titan after equinox in 2010 suddenly cooled in early 2012, which wasn’t predicted by models. Here the authors use observations to show that the increase in trace gases during the hot-spot resulted in radiative cooling feedback.
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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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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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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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Teanby NA, de Kok R, Irwin PGJ, Osprey S, Vinatier S, Gierasch PJ, Read PL, Flasar FM, Conrath BJ, Achterberg RK, Bézard B, Nixon CA, Calcutt SB. Titan's winter polar vortex structure revealed by chemical tracers. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008je003218] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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10
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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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Müller-Wodarg ICF, Yelle RV, Cui J, Waite JH. Horizontal structures and dynamics of Titan's thermosphere. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007je003033] [Citation(s) in RCA: 73] [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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12
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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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De La Haye V, Waite JH, Johnson RE, Yelle RV, Cravens TE, Luhmann JG, Kasprzak WT, Gell DA, Magee B, Leblanc F, Michael M, Jurac S, Robertson IP. Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere: Observation of a suprathermal corona. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006ja012222] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [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
| | - R. E. Johnson
- Astronomy Department; University of Virginia; Charlottesville Virginia USA
| | - R. V. Yelle
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
| | - T. E. Cravens
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
| | - J. G. Luhmann
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - W. T. Kasprzak
- NASA Goddard Space Flight Center; Greenbelt Maryland USA
| | - D. A. Gell
- Southwest Research Institute; San Antonio Texas USA
| | - B. Magee
- Southwest Research Institute; San Antonio Texas USA
| | - F. Leblanc
- Service d'Aéronomie du CNRS/IPSL; Paris France
| | - M. Michael
- Civil Engineering; Indian Institute of Technology; Kanpur India
| | - S. Jurac
- Center for Space Research; Massachusetts Institute of Technology; Cambridge Massachusetts USA
| | - I. P. Robertson
- Department of Physics and Astronomy; University of Kansas; Lawrence Kansas USA
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