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Pilkington NM, Achilleos N, Arridge CS, Guio P, Masters A, Ray LC, Sergis N, Thomsen MF, Coates AJ, Dougherty MK. Asymmetries observed in Saturn's magnetopause geometry. GEOPHYSICAL RESEARCH LETTERS 2015; 42:6890-6898. [PMID: 27609998 PMCID: PMC4994316 DOI: 10.1002/2015gl065477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Revised: 08/12/2015] [Accepted: 08/13/2015] [Indexed: 06/06/2023]
Abstract
For over 10 years, the Cassini spacecraft has patrolled Saturn's magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn-dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn-dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the "intrinsic" polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north-south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planet's magnetic dipole is tilted away from the Sun by 10-17°).
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Affiliation(s)
- N. M. Pilkington
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- Centre for Planetary Sciences at UCL/BirkbeckLondonUK
| | - N. Achilleos
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- Centre for Planetary Sciences at UCL/BirkbeckLondonUK
| | | | - P. Guio
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- Centre for Planetary Sciences at UCL/BirkbeckLondonUK
| | - A. Masters
- Blackett LaboratoryImperial College LondonLondonUK
| | - L. C. Ray
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- Centre for Planetary Sciences at UCL/BirkbeckLondonUK
| | - N. Sergis
- Office of Space Research and TechnologyAcademy of AthensAthensGreece
| | | | - A. J. Coates
- Centre for Planetary Sciences at UCL/BirkbeckLondonUK
- Mullard Space Science Laboratory, Department of Space and Climate PhysicsUniversity College LondonDorkingUK
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Pilkington NM, Achilleos N, Arridge CS, Guio P, Masters A, Ray LC, Sergis N, Thomsen MF, Coates AJ, Dougherty MK. Internally driven large-scale changes in the size of Saturn's magnetosphere. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2015; 120:7289-7306. [PMID: 27867793 PMCID: PMC5111417 DOI: 10.1002/2015ja021290] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 07/22/2015] [Accepted: 07/26/2015] [Indexed: 05/20/2023]
Abstract
Saturn's magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system's dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10-15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively "plasma-loaded" or "plasma-depleted" states, defined in terms of the internal suprathermal plasma pressure.
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Affiliation(s)
- N. M. Pilkington
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- The Centre for Planetary SciencesUCL/BirkbeckLondonUK
| | - N. Achilleos
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- The Centre for Planetary SciencesUCL/BirkbeckLondonUK
| | | | - P. Guio
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- The Centre for Planetary SciencesUCL/BirkbeckLondonUK
| | - A. Masters
- Blackett LaboratoryImperial College LondonLondonUK
| | - L. C. Ray
- Atmospheric Physics Laboratory, Department of Physics and AstronomyUniversity College LondonLondonUK
- The Centre for Planetary SciencesUCL/BirkbeckLondonUK
| | - N. Sergis
- Academy of AthensOffice of Space Research and TechnologyAthensGreece
| | | | - A. J. Coates
- The Centre for Planetary SciencesUCL/BirkbeckLondonUK
- Mullard Space Science Laboratory, Department of Space and Climate PhysicsUniversity College LondonDorkingUK
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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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Lai HR, Wei HY, Russell CT, Arridge CS, Dougherty MK. Reconnection at the magnetopause of Saturn: Perspective from FTE occurrence and magnetosphere size. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011ja017263] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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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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Clarke KE, Andrews DJ, Arridge CS, Coates AJ, Cowley SWH. Magnetopause oscillations near the planetary period at Saturn: Occurrence, phase, and amplitude. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja014745] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- K. E. Clarke
- Department of Physics and Astronomy; University of Leicester; Leicester United Kingdom
| | - D. J. Andrews
- Department of Physics and Astronomy; University of Leicester; Leicester United Kingdom
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; Dorking United Kingdom
- The Centre for Planetary Sciences at University College London/Birkbeck; London United Kingdom
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; Dorking United Kingdom
- The Centre for Planetary Sciences at University College London/Birkbeck; London United Kingdom
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester United Kingdom
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Zieger B, Hansen KC, Gombosi TI, De Zeeuw DL. Periodic plasma escape from the mass-loaded Kronian magnetosphere. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja014951] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- B. Zieger
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - K. C. Hansen
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - T. I. Gombosi
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
| | - D. L. De Zeeuw
- Department of Atmospheric, Oceanic and Space Sciences; University of Michigan; Ann Arbor Michigan USA
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Masters A, Achilleos N, Kivelson MG, Sergis N, Dougherty MK, Thomsen MF, Arridge CS, Krimigis SM, McAndrews HJ, Kanani SJ, Krupp N, Coates AJ. Cassini observations of a Kelvin-Helmholtz vortex in Saturn's outer magnetosphere. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2010ja015351] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- A. Masters
- Space and Atmospheric Physics Group, Blackett Laboratory; Imperial College London; London UK
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
- Center for Planetary Sciences; University College London; London UK
| | - N. Achilleos
- Center for Planetary Sciences; University College London; London UK
- Atmospheric Physics Laboratory, Department of Physics and Astronomy; University College London; London UK
| | - M. G. Kivelson
- Institute of Geophysics and Planetary Physics; University of California; Los Angeles California USA
| | - N. Sergis
- Office of Space Research and Technology; Academy of Athens; Athens Greece
| | - M. K. Dougherty
- Space and Atmospheric Physics Group, Blackett Laboratory; Imperial College London; London UK
| | - M. F. Thomsen
- Space Science and Applications; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - C. S. Arridge
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
- Center for Planetary Sciences; University College London; London UK
| | - S. M. Krimigis
- Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
| | - H. J. McAndrews
- Space Science and Applications; Los Alamos National Laboratory; Los Alamos New Mexico USA
| | - S. J. Kanani
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
- Center for Planetary Sciences; University College London; London UK
| | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany
| | - A. J. Coates
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
- Center for Planetary Sciences; University College London; London UK
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Kanani SJ, Arridge CS, Jones GH, Fazakerley AN, McAndrews HJ, Sergis N, Krimigis SM, Dougherty MK, Coates AJ, Young DT, Hansen KC, Krupp N. A new form of Saturn's magnetopause using a dynamic pressure balance model, based on in situ, multi-instrument Cassini measurements. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja014262] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- S. J. Kanani
- Mullard Space Science Laboratory; University College London; London UK
| | - C. S. Arridge
- Mullard Space Science Laboratory; University College London; London UK
| | - G. H. Jones
- Mullard Space Science Laboratory; University College London; London UK
| | - A. N. Fazakerley
- Mullard Space Science Laboratory; University College London; London UK
| | | | | | - S. M. Krimigis
- Applied Physics Laboratory; Johns Hopkins University; Baltimore Maryland USA
| | | | - A. J. Coates
- Mullard Space Science Laboratory; University College London; London UK
| | - D. T. Young
- Southwest Research Institute; San Antonio Texas USA
| | | | - N. Krupp
- Max-Planck-Institut für Sonnensystemforschung; Katlenberg-Lindau Germany
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Clarke KE, Andrews DJ, Coates AJ, Cowley SWH, Masters A. Magnetospheric period oscillations of Saturn's bow shock. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009ja015164] [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)
- K. E. Clarke
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - D. J. Andrews
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - A. J. Coates
- Mullard Space Science Laboratory; University College London; Dorking UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
| | - S. W. H. Cowley
- Department of Physics and Astronomy; University of Leicester; Leicester UK
| | - A. Masters
- Mullard Space Science Laboratory; University College London; Dorking UK
- Centre for Planetary Sciences at UCL/Birkbeck; London UK
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Bertucci CL. Characteristics and variability of Titan's magnetic environment. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2009; 367:789-798. [PMID: 19073462 DOI: 10.1098/rsta.2008.0250] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The structure and variability of Saturn's magnetic field in the vicinity of Titan's orbit is studied. In the dawn magnetosphere, the magnetic field presents a significant radial component directed towards Saturn, suggesting that Titan is usually located below the planet's warped and dynamic magnetodisc. Also, a non-negligible component along the co-rotation direction suggests that Saturn's magnetic field lines close to the magnetodisc are being swept back from their respective magnetic meridians. In the noon sector, Titan seems to be closer to the magnetodisc central current sheet, as the field lines in this region seem to be more dipolar. The distance between the central current sheet and Titan depends mainly on the solar wind pressure. Also, delta|B|/|B| approximately 0.5 amplitude waveforms at periods close to Saturn's kilometric radiation period are present in the background magnetic field. This modulation in the field is ubiquitous in Saturn's magnetosphere and associated with the presence of a rotating asymmetry in the planet's magnetic field.
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Affiliation(s)
- César L Bertucci
- Space and Atmospheric Physics Group, Imperial College London, London SW7 2BZ, UK.
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Masters A, Achilleos N, Dougherty MK, Slavin JA, Hospodarsky GB, Arridge CS, Coates AJ. An empirical model of Saturn's bow shock: Cassini observations of shock location and shape. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008ja013276] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- A. Masters
- Space and Atmospheric Physics Group, The Blackett Laboratory; Imperial College London; London UK
| | - N. Achilleos
- Atmospheric Physics Laboratory, Department of Physics and Astronomy; University College London; London UK
| | - M. K. Dougherty
- Space and Atmospheric Physics Group, The Blackett Laboratory; Imperial College London; London UK
| | - J. A. Slavin
- Heliophysics Science Division; NASA GSFC; Greenbelt Maryland USA
| | - G. B. Hospodarsky
- Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
| | - C. S. Arridge
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
- Centre for Planetary Sciences; University College London; London UK
| | - A. J. Coates
- Mullard Space Science Laboratory, Department of Space and Climate Physics; University College London; Dorking UK
- Centre for Planetary Sciences; University College London; London UK
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