Abstract
Hydrocarbons in the upper atmosphere of Saturn are known, from Voyager,
ground-based, and early Cassini results, to vary in emission intensity
with latitude. Of particular interest is the marked increase in
hydrocarbon line intensity near the south pole during southern summer,
as the increased line intensity cannot be simply explained by the
increased temperatures observed in that region since the variations
between C2H2 and C2H6
emission in the south pole region are different. In order to measure the
latitudinal variations of hydrocarbons in Saturn's southern hemisphere
we have used 3 cm-1 resolution Cassini CIRS data from 2006
and combined this with measurements from the ground in October 2006 at
NASA's IRTF using Celeste, an infrared high-resolution cryogenic grating
spectrometer. These two data sets have been used to infer the molecular
abundances of C2H2 and C2H6
across the southern hemisphere in the 1-10 mbar altitude region. We find
that the latitudinal acetylene profile follows the yearly average mean
daily insolation except at the southern pole where it peaks in
abundance. Near the equator (5° S) the C2H2
abundance at the 1.2 mbar level is (1.6 ± 0.19)
×10-7 and it decreases by a factor of 2.7 from the
equator toward the pole. However, at the pole (∼87° S) the
C2H2 abundance jumps to (1.8 ± 0.3)
×10-7, approximately the equatorial value. The
C2H6 abundance near the equator at the 2 mbar
level is (0.7 ± 0.1) ×10-5 and stays
approximately constant until mid-latitudes where it increases gradually
toward the pole, attaining a value of (1.4 ± 0.4)
×10-5 there. The increase in ethane toward the pole
with the corresponding decrease in acetylene is consistent with southern
hemisphere meridional winds [Greathouse, T.K., Lacy, J.H.,
Bézard, B., Moses, J.I., Griffith, C.A., Richter, M.J., 2005.
Icarus 177, 18-31]. The localized increase in acetylene at the pole
provides evidence that there is dynamical transport of hydrocarbons from
the equator to the southern pole.
| Original language | English |
|---|---|
| Pages (from-to) | 249-259 |
| Number of pages | 11 |
| Journal | Icarus |
| Volume | 202 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 1 Jul 2009 |
| Externally published | Yes |
Bibliographical note
Funding Information:The authors wish to thank the NASA Infrared Telescope staff for their assistance during the observations. The Cassini/CIRS team is recognized for their work in sequence planning, data reduction, and calibration. This research was supported in part by the NASA Planetary Astronomy Program. B.E. Hesman was supported by a NASA Postdoctoral Program Fellowship appointment conducted at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. B.E. Hesman is currently supported by the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Incorporated. D.E.J., G.L.B., R.K.A., A.A.S.-M., and C.A.N. acknowledge the continuing support of the NASA Cassini Mission. C.M. Anderson was supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. L.N. Fletcher was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by Oak Ridge Associated Universities through a contract with NASA.
Copyright:
Copyright 2009 Elsevier B.V., All rights reserved.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science