Asymmetries observed in Saturn's magnetopause geometry.
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°).
Atmospheric Physics Laboratory, Department of Physics and Astronomy University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK.
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Pilkington
Atmospheric Physics Laboratory, Department of Physics and Astronomy University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK.
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Achilleos
Physics Department Lancaster University Lancaster UK.
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Arridge
Atmospheric Physics Laboratory, Department of Physics and Astronomy University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK.
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0000-0002-1607-5862
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Guio
Blackett Laboratory Imperial College London London UK.
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Masters
Atmospheric Physics Laboratory, Department of Physics and Astronomy University College London London UK; Centre for Planetary Sciences at UCL/Birkbeck London UK.
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Ray
Office of Space Research and Technology Academy of Athens Athens Greece.
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Sergis
Planetary Science Institute Tucson Arizona USA.
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Thomsen
Centre for Planetary Sciences at UCL/Birkbeck London UK; Mullard Space Science Laboratory, Department of Space and Climate Physics University College London Dorking UK.
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0000-0002-6185-3125
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Coates
Blackett Laboratory Imperial College London London UK.
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Dougherty
Saturn; asymmetry; magnetopause; magnetosphere; plasma; season