Cassini VIMS observations of H3+ emission on the nightside of Jupiter

Stallard, Tom S. and Melin, Henrik and Miller, Steve and Badman, Sarah V. and Baines, Kevin H. and Brown, Robert H. and Blake, James S. D. and O'Donoghue, James and Johnson, Rosie E. and Bools, Bethany and Pilkington, Nathan M. and East, Oliver T.L. and Fletcher, Mark (2015) Cassini VIMS observations of H3+ emission on the nightside of Jupiter. Journal of Geophysical Research: Space Physics, 120 (8). pp. 6948-6973. ISSN 2169-9402

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We present the first detailed analysis of H3+ nightside emission from Jupiter, using Visual and Infrared Mapping Spectrometer (VIMS) data from the Cassini flyby in 2000–2001, producing the first Jovian maps of nightside H3+ emission, temperature, and column density. Using these, we identify and characterize regions of H3+ nightside emission, compared against past observations of H3+ emission on the dayside. We focus our investigation on the region previously described as “mid-to-low latitude emission,” the source for which has been controversial. We find that the brightest of this emission is generated at Jovigraphic latitudes similar to the most equatorward extent of the main auroral emission but concentrated at longitudes eastward of this emission. The emission is produced by enhanced H3+ density, with temperatures dropping away in this region. This emission has a loose association with the predicted location of diffuse aurora produced by pitch angle scattering in the north, but not in the south. This emission also lays in the path of subrotating winds flowing from the aurora, suggesting a transport origin. Some differences are seen between dayside and nightside subauroral emissions, with dayside emission extending more equatorward, perhaps caused by the lack of sunlight ionization on the nightside, and unmeasured changes in temperature. Ionospheric temperatures are hotter in the polar region (~1100–1500 K), dropping away toward the equator (as low as 750 K), broadly similar to values on the dayside, highlighting the dominance of auroral effects in the polar region. No equatorial emission is observed, suggesting that very little particle precipitation occurs away from the polar regions.

Item Type:
Journal Article
Journal or Publication Title:
Journal of Geophysical Research: Space Physics
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© 2015 American Geophysical Union
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Deposited On:
21 Oct 2015 05:00
Last Modified:
17 Sep 2023 01:42