Saturn's variable thermosphere from Cassini/UVIS occultations

T. T. Koskinen, B. R. Sandel, Roger Yelle, D. F. Strobel, I. C F Müller-Wodarg, J. T. Erwin

Research output: Contribution to journalArticle

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Abstract

We retrieved the density and temperature profiles in Saturn's thermosphere from 26 stellar occultations observed by the Cassini/UVIS instrument. These results expand upon and complement the previous analysis of 15 Cassini/UVIS solar occultations by Saturn's upper thermosphere. We find that the exospheric temperatures based on the stellar occultations agree with the solar occultations and range from 380. K to 590. K. These temperatures are also consistent with the recent re-analysis of the Voyager/UVS occultations. The retrieved density profiles support our earlier inference that the shape of the atmosphere at low pressures is consistent with a meridional trend of increasing temperatures with absolute latitude. This implies a high-latitude heat source, such as auroral heating, although the existing circulation models that include auroral heating still underestimate the equatorial temperatures by overestimating the meridional temperature gradient. This suggests either that the circulation models are somehow incomplete or there is some other heat source at low to mid latitudes that is relatively less efficient than high-latitude heating. We also find evidence for the expansion of the exobase by about 500. km between 2006 and 2011 near the equator, followed by possible contraction after 2011. The expansion appears to be caused by significant warming of the lower thermosphere that anti-correlates with solar activity and may be connected to changes in global circulation. Lastly, we note that our density profiles are in good general agreement with the Voyager/UVS data. In particular, the Voyager density profiles are most consistent with the Cassini/UVIS stellar occultations from late 2008 and early 2009 that roughly coincide in season with the Voyager flybys.

Original languageEnglish (US)
Pages (from-to)174-189
Number of pages16
JournalIcarus
Volume260
DOIs
StatePublished - Nov 1 2015

Fingerprint

thermosphere
occultation
stellar occultation
Saturn
heating
heat source
heat sources
profiles
polar regions
temperature
expansion
equators
solar activity
inference
temperature profile
complement
temperature profiles
temperature gradient
contraction
low pressure

Keywords

  • Aeronomy
  • Atmospheres, structure
  • Occultations
  • Saturn

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Koskinen, T. T., Sandel, B. R., Yelle, R., Strobel, D. F., Müller-Wodarg, I. C. F., & Erwin, J. T. (2015). Saturn's variable thermosphere from Cassini/UVIS occultations. Icarus, 260, 174-189. https://doi.org/10.1016/j.icarus.2015.07.008

Saturn's variable thermosphere from Cassini/UVIS occultations. / Koskinen, T. T.; Sandel, B. R.; Yelle, Roger; Strobel, D. F.; Müller-Wodarg, I. C F; Erwin, J. T.

In: Icarus, Vol. 260, 01.11.2015, p. 174-189.

Research output: Contribution to journalArticle

Koskinen, TT, Sandel, BR, Yelle, R, Strobel, DF, Müller-Wodarg, ICF & Erwin, JT 2015, 'Saturn's variable thermosphere from Cassini/UVIS occultations', Icarus, vol. 260, pp. 174-189. https://doi.org/10.1016/j.icarus.2015.07.008
Koskinen TT, Sandel BR, Yelle R, Strobel DF, Müller-Wodarg ICF, Erwin JT. Saturn's variable thermosphere from Cassini/UVIS occultations. Icarus. 2015 Nov 1;260:174-189. https://doi.org/10.1016/j.icarus.2015.07.008
Koskinen, T. T. ; Sandel, B. R. ; Yelle, Roger ; Strobel, D. F. ; Müller-Wodarg, I. C F ; Erwin, J. T. / Saturn's variable thermosphere from Cassini/UVIS occultations. In: Icarus. 2015 ; Vol. 260. pp. 174-189.
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