Jupiter's Stratospheric Hydrocarbons: From Voyager to Cassini

Details Jupiter's Stratospheric Hydrocarbons: From Voyager to Cassini Jupiter's Stratospheric Hydrocarbons: From Voyager to Cassini

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.1010n&link_type=abstract

American Astronomical Society, DPS meeting #41, #10.10

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Scientific paper

Photolysis of methane gas in Jupiter's atmosphere by solar UV creates short-lived radical species, which subsequently recombine to form stable higher-mass hydrocarbons including acetylene (C2H2) and ethane (C2H6). With dramatically different photochemical lifetimes (3x107 s and 3x1010 s respectively at 5 mbar), these gases may be used as tracers of atmospheric circulation. For example, while ethane's lifetime greatly exceeds the predicted dynamical timescale for meridional mixing inferred from comet SL-9 debris (5-50 x108 s), the lifetime of acetylene is much less, and therefore different latitude distributions of these species are expected.
In a recent paper (Nixon et al. 2007), infrared spectra acquired by the Cassini CIRS instrument during the Jupiter encounter of December 2000 were modeled to recover the meridional variations of both gases in the stratosphere (5 mbar) and upper troposphere (200 mbar). In this work, we have applied the same analysis to spectra acquired by Voyager IRIS 21 years earlier (1.75 Jupiter years), recovering the stratospheric variation. Some striking similarities and differences are evident: while the acetylene distribution in 1979 does not show the strong North-South hemispheric asymmetry seen in 2000, ethane on the other hand shows qualitatively a similar picture in the two epochs.
In this presentation we show the meridional abundance variations from both of these important spacecraft datasets and discuss how the interplay of photochemistry and dynamics may explain the results. We also discuss how these findings relate to the current understanding of Jupiter's atmosphere, and suggest directions of future research.
We acknowledge the support of the Cassini-Huygens Project and NASA Grant 07-OPR07-0048.
References:
C. A. Nixon et al., Icarus, 188, pp. 47-71, 2007.

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