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Peak emission altitude of Saturn's H 3 + aurora
Author(s) -
Stallard Tom S.,
Melin Henrik,
Miller Steve,
Badman Sarah V.,
Brown Robert H.,
Baines Kevin H.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl052806
Subject(s) - altitude (triangle) , physics , ionosphere , saturn , scale height , atmospheric sciences , planet , emission spectrum , astrophysics , astronomy , geometry , spectral line , mathematics
Here we present the first detailed measurement of the altitudinal profile of H 3 + emission within Saturn's ionosphere, made using images taken by the VIMS instrument on Cassini on 11–12 October 2006, during a chance alignment between the visible limb of the planet and the position of the main auroral emission. Using this, we show that the emission profile of H 3 + can be fitted to a reasonable accuracy with a Gaussian, producing a calculated peak emission altitude at 1155 (±25) km that differs significantly from previous observations of the UV emission profile, and also from the predictions of models that calculated the H 3 + emission profile, which suggested that there would be extended emission above the peak emission altitude. This lack of extended emission is most simply explained by differences in the scale height of H and H 2 , suggesting that models overestimate H 2 at high altitudes, with little H 2 from 2000 km above the 1 bar level.