Rights statement: Accepted for publication in Journal of Geophysical Research: Space Physics. Copyright 2019 American Geophysical Union. Further reproduction or electronic distribution is not permitted.
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Available under license: CC BY: Creative Commons Attribution 4.0 International License
Final published version
Licence: CC BY: Creative Commons Attribution 4.0 International License
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Energetic particle signatures above Saturn’s aurorae
AU - Bader, Alexander
AU - Badman, Sarah
AU - Ray, Licia C
AU - Paranicas, C.
AU - Lorch, Chris
AU - Clark, George
AU - Andre, Mats
AU - Mitchell, Donald G.
AU - Constable, David A.
AU - Kinrade, Joe
AU - Hunt, Gregory
AU - Pryor, W. R.
N1 - Accepted for publication in Journal of Geophysical Research: Space Physics. Copyright 2019 American Geophysical Union. Further reproduction or electronic distribution is not permitted.
PY - 2020/1/1
Y1 - 2020/1/1
N2 - Near the end of its mission, NASA's Cassini spacecraft performed several low‐altitude passes across Saturn's auroral region. We present auroral imagery and various coincident particle and field measurements of two such passes, providing important information about the structure and dynamics of Saturn's auroral acceleration region. In upward field‐aligned current regions, upward proton beams are observed to reach energies of several tens of keV; the associated precipitating electron populations are found to have mean energies of about 10 keV. With no significant wave activity being apparent, these findings indicate strong parallel potentials responsible for auroral acceleration; about 100 times stronger than at Earth. This is further supported by observations of proton conics in downward field‐aligned current regions above the acceleration region, which feature a lower energy cutoff above ~50 keV ‐ indicating energetic proton populations trapped by strong parallel potentials while being transversely energized until they can overcome the trapping potential, likely through wave‐particle interactions. A spacecraft pass through a downward current region at an altitude near the acceleration region reveals plasma wave features which may be driving the transverse proton acceleration generating the conics. Overall, the signatures observed resemble those related to the terrestrial and Jovian aurorae, the particle energies and potentials at Saturn appearing to be significantly higher than at Earth and comparable to those at Jupiter.
AB - Near the end of its mission, NASA's Cassini spacecraft performed several low‐altitude passes across Saturn's auroral region. We present auroral imagery and various coincident particle and field measurements of two such passes, providing important information about the structure and dynamics of Saturn's auroral acceleration region. In upward field‐aligned current regions, upward proton beams are observed to reach energies of several tens of keV; the associated precipitating electron populations are found to have mean energies of about 10 keV. With no significant wave activity being apparent, these findings indicate strong parallel potentials responsible for auroral acceleration; about 100 times stronger than at Earth. This is further supported by observations of proton conics in downward field‐aligned current regions above the acceleration region, which feature a lower energy cutoff above ~50 keV ‐ indicating energetic proton populations trapped by strong parallel potentials while being transversely energized until they can overcome the trapping potential, likely through wave‐particle interactions. A spacecraft pass through a downward current region at an altitude near the acceleration region reveals plasma wave features which may be driving the transverse proton acceleration generating the conics. Overall, the signatures observed resemble those related to the terrestrial and Jovian aurorae, the particle energies and potentials at Saturn appearing to be significantly higher than at Earth and comparable to those at Jupiter.
U2 - 10.1029/2019JA027403
DO - 10.1029/2019JA027403
M3 - Journal article
VL - 125
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9402
IS - 1
M1 - e2019JA027403
ER -