TY - JOUR
T1 - TITAN'S UPPER ATMOSPHERE from CASSINI/UVIS SOLAR OCCULTATIONS
AU - Capalbo, Fernando J.
AU - Bénilan, Yves
AU - Yelle, Roger V.
AU - Koskinen, Tommi T.
N1 - Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved..
PY - 2015/12/1
Y1 - 2015/12/1
N2 - Titan's atmosphere is composed mainly of molecular nitrogen, methane being the principal trace gas. From the analysis of 8 solar occultations measured by the Extreme Ultraviolet channel of the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini, we derived vertical profiles of N2 in the range 1100-1600 km and vertical profiles of CH4 in the range 850-1300 km. The correction of instrument effects and observational effects applied to the data are described. We present CH4 mole fractions, and average temperatures for the upper atmosphere obtained from the N2 profiles. The occultations correspond to different times and locations, and an analysis of variability of density and temperature is presented. The temperatures were analyzed as a function of geographical and temporal variables, without finding a clear correlation with any of them, although a trend of decreasing temperature toward the north pole was observed. The globally averaged temperature obtained is (150 ± 1) K. We compared our results from solar occultations with those derived from other UVIS observations, as well as studies performed with other instruments. The observational data we present confirm the atmospheric variability previously observed, add new information to the global picture of Titan's upper atmosphere composition, variability, and dynamics, and provide new constraints to photochemical models.
AB - Titan's atmosphere is composed mainly of molecular nitrogen, methane being the principal trace gas. From the analysis of 8 solar occultations measured by the Extreme Ultraviolet channel of the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini, we derived vertical profiles of N2 in the range 1100-1600 km and vertical profiles of CH4 in the range 850-1300 km. The correction of instrument effects and observational effects applied to the data are described. We present CH4 mole fractions, and average temperatures for the upper atmosphere obtained from the N2 profiles. The occultations correspond to different times and locations, and an analysis of variability of density and temperature is presented. The temperatures were analyzed as a function of geographical and temporal variables, without finding a clear correlation with any of them, although a trend of decreasing temperature toward the north pole was observed. The globally averaged temperature obtained is (150 ± 1) K. We compared our results from solar occultations with those derived from other UVIS observations, as well as studies performed with other instruments. The observational data we present confirm the atmospheric variability previously observed, add new information to the global picture of Titan's upper atmosphere composition, variability, and dynamics, and provide new constraints to photochemical models.
KW - occultations
KW - planets and satellites: atmospheres
KW - planets and satellites: composition
KW - planets and satellites: individual (Titan)
KW - techniques: imaging spectroscopy
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U2 - 10.1088/0004-637X/814/2/86
DO - 10.1088/0004-637X/814/2/86
M3 - Article
AN - SCOPUS:84948800197
SN - 0004-637X
VL - 814
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 86
ER -