TY - JOUR
T1 - Energetic Particle Signatures Above Saturn's Aurorae
AU - Bader, A.
AU - Badman, S. V.
AU - Ray, L. C.
AU - Paranicas, C. P.
AU - Lorch, C.T.S.
AU - Clark, G.
AU - André, M.
AU - Mitchell, D. G.
AU - Constable, D. A.
AU - Kinrade, J.
AU - Hunt, G. J.
AU - Pryor, W.
N1 - Funding Information:
Cassini operations are supported by NASA (managed by the Jet Propulsion Laboratory) and European Space Agency (ESA). All data used in this study is available on NASA's Planetary Data System (PDS) (https://pds.jpl.nasa.gov/). A. B. was funded by a Lancaster University FST studentship. S. V. B., L. C. R., D. A. C., and J. K. were supported by STFC Grant ST/R000816/1. S. V. B. was also supported by an STFC Ernest Rutherford FellowshipST/M005534/1. G. J. H. was supported by STFC Grant ST/N000692/1.
Publisher Copyright:
© 2019. The Authors.
PY - 2020/1/9
Y1 - 2020/1/9
N2 - Near the end of its mission, NASA's Cassini spacecraft performed several low-altitude passes across Saturn's auroral region. We present ultraviolet 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 (Formula presented.) 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 ultraviolet 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 (Formula presented.) 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.
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U2 - 10.1029/2019JA027403
DO - 10.1029/2019JA027403
M3 - Article
AN - SCOPUS:85081018068
SN - 2169-9380
VL - 125
SP - 1
EP - 17
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 1
M1 - e2019JA027403
ER -