Seasonal variations in Saturn's plasma sheet warping

• Published in: Geophysical research letters Vol. 43; no. 23; pp. 11,957 - 11,962
• Main Authors: Carbary, J. F., Mitchell, D. G.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.12.2016
• Subjects: bowl model; Cassini mission; Celestial bodies; Concavity; Direction; Dynamical systems; Dynamics; Energetic neutral atoms; Geometry; Hinges; Hydrogen; Latitude; Magnetometers; Magnetospheres; Mathematical models; Neutral atoms; Oxygen; Parameters; Plasma; Saturn; Saturn (planet); Saturn magnetodisk; Seasonal variation; Seasonal variations; Shape; Sheets; Solar system; Solar wind; Solstices; Stellar mass; Sun; Warpage; Warping
• ISSN: 0094-8276; 1944-8007; 1944-8007
• DOI: 10.1002/2016GL071790

Composite images of hydrogen and oxygen energetic neutral atoms (ENA) obtained from 2005 through 2015 from the Ion Neutral Camera on Cassini reveal the structure of Saturn's plasma sheet out to ~40 Rs (1 Rs = 60,268 km). Seen from either the dawnside or duskside at low latitude, these composites reveal that the plasma sheet is concave upward (northward) near Saturn's southern solstice, has no concavity near equinox, and is concave downward (southward) near Saturn's northern solstice. This seasonal variation confirms the Arridge “bowl” model developed early in the Cassini mission based on limited magnetometer data, with the concavity depending on the tangent of the Sun's latitude at Saturn and a “hinge” parameter rH. The best fits to the ENA data indicate rH ≈ 25–30 Rs, which is close to the 29 Rs originally suggested by the magnetometer results. The bowl structure suggests other magnetodisks in the solar system and beyond may also undergo similar warping dynamics and may not have a “flat” geometry. Plain Language Summary Saturn's plasma sheet, also called a magnetodisk, does not have a flat geometry, but rather has a bowl shape that warps north or south depending on the seasonal direction of the solar wind. Using over 10 years of observations, composite ENA images have for the first time been used to validate a seasonal model of Saturn's magnetodisk. The magnetodisk warping also implies that other planetary and astronomical magnetospheres, subject to similar plasma winds, may not have a simple “flat” geometry as usually depicted. Key Points Saturn's plasma sheet has a bowl‐like shape defined by a hinge parameter and solar latitude The bowl concavity varies with seasons according to Arridge model with hinge parameter 25‐30 Rs First use of long‐term ENA observations to confirm seasonal variations in any planetary magnetosphere