Origin of Saturn's aurora: Simultaneous observations by Cassini and the Hubble Space Telescope

Outer planet auroras have been imaged for more than a decade, yet understanding their physical origin requires simultaneous remote and in situ observations. The first such measurements at Saturn were obtained in January 2007, when the Hubble Space Telescope imaged the ultraviolet aurora, while the Cassini spacecraft crossed field lines connected to the auroral oval in the high-latitude magnetosphere near noon. The Cassini data indicate that the noon aurora lies in the boundary between open- and closed-field lines, where a layer of upward-directed field-aligned current flows whose density requires downward acceleration of magnetospheric electrons sufficient to produce the aurora. These observations indicate that the quasi-continuous main oval is produced by the magnetosphere-solar wind interaction through the shear in rotational flow across the open-closed-field line boundary.

[1]  Emma J. Bunce,et al.  Variable morphology of Saturn's southern ultraviolet aurora , 2005 .

[2]  Kevin J. Madders,et al.  EUROPEAN SPACE AGENCY , 1983 .

[3]  Denis Grodent,et al.  Characteristics of Saturn's FUV aurora observed with the Space Telescope Imaging Spectrograph , 2004 .

[4]  Emma J. Bunce,et al.  Origin of the main auroral oval in Jupiter's coupled magnetosphere–ionosphere system , 2001 .

[5]  Michel Blanc,et al.  Saturn's Auroral Response to the Solar Wind: Centrifugal Instability Model , 2006 .

[6]  J. A. Koehler,et al.  Parallel Electric Fields , 1973 .

[7]  Mario H. Acuna,et al.  Currents in Saturn's magnetosphere , 1983 .

[8]  Emma J. Bunce,et al.  Cassini observations of the variation of Saturn's ring current parameters with system size , 2007 .

[9]  David J. Southwood,et al.  A new perspective concerning the influence of the solar wind on the Jovian magnetosphere , 2001 .

[10]  Denis Grodent,et al.  A statistical analysis of the location and width of Saturn's southern auroras , 2006 .

[11]  Philippe Zarka,et al.  Jupiter's Aurora , 2007 .

[12]  N Achilleos,et al.  Cassini Magnetometer Observations During Saturn Orbit Insertion , 2005, Science.

[13]  Emma J. Bunce,et al.  Open flux estimates in Saturn's magnetosphere during the January 2004 Cassini‐HST campaign, and implications for reconnection rates , 2005 .

[14]  T. Hill,et al.  The Jovian auroral oval , 2001 .

[15]  Kenneth C. Hansen,et al.  Statistical validation of a solar wind propagation model from 1 to 10 AU , 2008 .

[16]  Emma J. Bunce,et al.  Magnetic field structure of Saturn's dayside magnetosphere and its mapping to the ionosphere: Results from ring current modeling , 2008 .

[17]  Stephen Knight,et al.  Parallel electric fields , 1973 .

[18]  Christopher T. Russell,et al.  Modeling the size and shape of Saturn's magnetopause with variable dynamic pressure , 2006 .

[19]  Emma J. Bunce,et al.  Corotation-driven magnetosphere-ionosphere coupling currents in Saturn's magnetosphere and their relation to the auroras , 2003 .

[20]  B. Cecconi,et al.  An Earth-like correspondence between Saturn's auroral features and radio emission , 2005, Nature.

[21]  Edward J. Smith,et al.  A model of Saturn's magnetic field based on all available data , 1990 .

[22]  Emma J. Bunce,et al.  A simple quantitative model of plasma flows and currents in Saturn's polar ionosphere , 2004 .

[23]  Emma J. Bunce,et al.  Saturn's Polar Ionospheric Flows and Their Relation to the Main Auroral Oval , 2022 .

[24]  D. Grodent,et al.  Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter , 2005, Nature.

[25]  Emma J. Bunce,et al.  Reconnection in a rotation-dominated magnetosphere and its relation to Saturn's auroral dynamics , 2005 .