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Saturn's near-equatorial ionospheric conductivities from in situ measurements. Sci Rep 2020; 10:7932. [PMID: 32404966 PMCID: PMC7220909 DOI: 10.1038/s41598-020-64787-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 04/21/2020] [Indexed: 11/08/2022] Open
Abstract
Cassini's Grand Finale orbits provided for the first time in-situ measurements of Saturn's topside ionosphere. We present the Pedersen and Hall conductivities of the top near-equatorial dayside ionosphere, derived from the in-situ measurements by the Cassini Radio and Wave Plasma Science Langmuir Probe, the Ion and Neutral Mass Spectrometer and the fluxgate magnetometer. The Pedersen and Hall conductivities are constrained to at least 10-5-10-4 S/m at (or close to) the ionospheric peak, a factor 10-100 higher than estimated previously. We show that this is due to the presence of dusty plasma in the near-equatorial ionosphere. We also show the conductive ionospheric region to be extensive, with thickness of 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities from orbit 288 to 292.
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Stallard TS, Baines KH, Melin H, Bradley TJ, Moore L, O'Donoghue J, Miller S, Chowdhury MN, Badman SV, Allison HJ, Roussos E. Local-time averaged maps of H 3+ emission, temperature and ion winds. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2019; 377:20180405. [PMID: 31378177 PMCID: PMC6710899 DOI: 10.1098/rsta.2018.0405] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 06/19/2019] [Indexed: 05/20/2023]
Abstract
We present Keck-NIRSPEC observations of Saturn's [Formula: see text] aurora taken over a period of a month, in support of the Cassini mission's 'Grand Finale'. These observations produce two-dimensional maps of Saturn's [Formula: see text] temperature and ion winds for the first time. These maps show surprising complexity, with different morphologies seen in each night. The [Formula: see text] ion winds reveal multiple arcs of 0.5-1 km s-1 ion flows inside the main auroral emission. Although these arcs of flow occur in different locations each night, they show intricate structures, including mirrored flows on the dawn and dusk of the planet. These flows do not match with the predicted flows from models of either axisymmetric currents driven by the Solar Wind or outer magnetosphere, or the planetary periodic currents associated with Saturn's variable rotation rate. The average of the ion wind flows across all the nights reveals a single narrow and focused approximately 0.3 km s-1 flow on the dawn side and broader and more extensive 1-2 km s-1 sub-corotation, spilt into multiple arcs, on the dusk side. The temperature maps reveal sharp gradients in ionospheric temperatures, varying between 300 and 600 K across the auroral region. These temperature changes are localized, resulting in hot and cold spots across the auroral region. These appear to be somewhat stable over several nights, but change significantly over longer periods. The position of these temperature extremes is not well organized by the planetary period and there is no evidence for a thermospheric driver of the planetary period current system. Since no past magnetospheric or thermospheric models explain the rich complexity observed here, these measurements represent a fantastic new resource, revealing the complexity of the interaction between Saturn's thermosphere, ionosphere and magnetosphere. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.
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Affiliation(s)
- Tom S. Stallard
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
- e-mail:
| | - Kevin H. Baines
- Atmospheric Oceanic and Space Science University of Wisconsin-Madison, 1225 W Dayton St, Madison, WI 53706, USA
| | - Henrik Melin
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Thomas J. Bradley
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Luke Moore
- Center for Space Physics, Boston University, 725 Commonwealth Avenue, Room 506, Boston, MA 02215, USA
| | - James O'Donoghue
- Institute of Space and Astronautical Science, JAXA, Yoshinodai 3-1-1, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
| | - Steve Miller
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
| | - Mohammad N. Chowdhury
- Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Sarah V. Badman
- Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YW, UK
| | | | - Elias Roussos
- Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077, Goettingen, Germany
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Ray LC, Lorch CTS, O'Donoghue J, Yates JN, Badman SV, Smith CGA, Stallard TS. Why is the H 3+ hot spot above Jupiter's Great Red Spot so hot? PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2019; 377:20180407. [PMID: 31378179 PMCID: PMC6710891 DOI: 10.1098/rsta.2018.0407] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 05/22/2019] [Indexed: 06/10/2023]
Abstract
Recent observations of Jupiter's Great Red Spot indicate that the thermosphere above the storm is hotter than its surroundings by more than 700 K. Possible suggested sources for this heating have thus far included atmospheric gravity waves and lightning-driven acoustic waves. Here, we propose that Joule heating, driven by Great Red Spot vorticity penetrating up into the lower stratosphere and coupling to the thermosphere, may contribute to the large observed temperatures. The strength of Joule heating will depend on the local inclination angle of the magnetic field and thus the observed emissions and inferred temperatures should vary with planetary longitude as the Great Red Spot tracks across the planet. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.
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Affiliation(s)
- L. C. Ray
- Space & Planetary Physics, Lancaster University, Lancaster, UK
| | - C. T. S. Lorch
- Space & Planetary Physics, Lancaster University, Lancaster, UK
| | - J. O'Donoghue
- Goddard Space Flight Center, NASA, Greenbelt, MD, USA
| | - J. N. Yates
- European Space Agency, ESAC, Villanueva de la Canada, Spain
| | - S. V. Badman
- Space & Planetary Physics, Lancaster University, Lancaster, UK
| | | | - T. S. Stallard
- Department of Physics and Astronomy, University of Leicester, Leicester, UK
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Waite JH, Perryman RS, Perry ME, Miller KE, Bell J, Cravens TE, Glein CR, Grimes J, Hedman M, Cuzzi J, Brockwell T, Teolis B, Moore L, Mitchell DG, Persoon A, Kurth WS, Wahlund JE, Morooka M, Hadid LZ, Chocron S, Walker J, Nagy A, Yelle R, Ledvina S, Johnson R, Tseng W, Tucker OJ, Ip WH. Chemical interactions between Saturn’s atmosphere and its rings. Science 2018; 362:362/6410/eaat2382. [DOI: 10.1126/science.aat2382] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 09/10/2018] [Indexed: 11/03/2022]
Abstract
The Pioneer and Voyager spacecraft made close-up measurements of Saturn’s ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn’s atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft’s Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.
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O'Donoghue J, Stallard TS, Melin H, Jones GH, Cowley SWH, Miller S, Baines KH, Blake JSD. The domination of Saturn's low-latitude ionosphere by ring 'rain'. Nature 2013; 496:193-5. [PMID: 23579676 DOI: 10.1038/nature12049] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2012] [Accepted: 02/22/2013] [Indexed: 11/09/2022]
Abstract
Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring 'rain' is important in modulating ionospheric emissions and suppressing electron densities.
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Affiliation(s)
- J O'Donoghue
- Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK.
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Jia X, Kivelson MG. Driving Saturn's magnetospheric periodicities from the upper atmosphere/ionosphere: Magnetotail response to dual sources. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja018183] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Liu X, Hill TW. Effects of finite plasma pressure on centrifugally driven convection in Saturn's inner magnetosphere. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja017827] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Ray LC, Galand M, Moore LE, Fleshman B. Characterizing the limitations to the coupling between Saturn's ionosphere and middle magnetosphere. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja017735] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Jia X, Hansen KC, Gombosi TI, Kivelson MG, Tóth G, DeZeeuw DL, Ridley AJ. Magnetospheric configuration and dynamics of Saturn's magnetosphere: A global MHD simulation. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012ja017575] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Jia X, Kivelson MG, Gombosi TI. Driving Saturn's magnetospheric periodicities from the upper atmosphere/ionosphere. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011ja017367] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Galand M, Moore L, Mueller-Wodarg I, Mendillo M, Miller S. Response of Saturn's auroral ionosphere to electron precipitation: Electron density, electron temperature, and electrical conductivity. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016412] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Marina Galand
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Luke Moore
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Ingo Mueller-Wodarg
- Space and Atmospheric Physics Group, Department of Physics; Imperial College London; London UK
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Michael Mendillo
- Center for Space Physics; Boston University; Boston Massachusetts USA
| | - Steve Miller
- Atmospheric Physics Laboratory, Department of Physics and Astronomy; University College London; London UK
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Talboys DL, Bunce EJ, Cowley SWH, Arridge CS, Coates AJ, Dougherty MK. Statistical characteristics of field-aligned currents in Saturn's nightside magnetosphere. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010ja016102] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- D. L. Talboys
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - E. J. Bunce
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; London UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; London UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
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Liu X, Hill TW, Wolf RA, Sazykin S, Spiro RW, Wu H. Numerical simulation of plasma transport in Saturn's inner magnetosphere using the Rice Convection Model. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010ja015859] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- X. Liu
- Physics and Astronomy Department; Rice University; Houston Texas USA
| | - T. W. Hill
- Physics and Astronomy Department; Rice University; Houston Texas USA
| | - R. A. Wolf
- Physics and Astronomy Department; Rice University; Houston Texas USA
| | - S. Sazykin
- Physics and Astronomy Department; Rice University; Houston Texas USA
| | - R. W. Spiro
- Physics and Astronomy Department; Rice University; Houston Texas USA
| | - H. Wu
- Shell International Exploration and Production; Houston Texas USA
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