36th DPS Meeting, 8-12 November 2004
Session 30 Jupiter and Saturn: Composition, Structure, Dynamics
Oral, Thursday, November 11, 2004, 1:45-4:15pm, Clark

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[30.06] Vertical profiles of ammonia and phosphine on Saturn derived from Cassini/CIRS far-infrared observations.

P. G. J. Irwin, N. A. Teanby, S. B. Calcutt, F. W. Taylor, P. L. R. Read (AOPP, Oxford University), CIRS Investigation Team

During Cassini's approach to the Saturnian system, where it arrived on 30th June 2004, many observations of the infrared spectrum of Saturn were recorded. A particularly useful set of observations was recorded on June 19th 2004 covering the range 10-600 cm-1 at a resolution of 0.5 cm-1 and sampling regions at 35S and 60S with a FOV of radius equal to 27 degrees of latitude at the equator. The average of these observations at the two different latitudes have been analysed with a retrieval model to determine vertical profiles of temperature, para-hydrogen fraction, ammonia and phosphine.

The results of these preliminary retrievals will be presented. We find that both the derived temperature and para-hydrogen profiles are consistent with previous analyses. We have also determined the phosphine profile in the upper troposphere. At 35S we estimate the abundance of phosphine to be 8e-6 at 595 mb reducing to 5e-7 at 160 mb while at 60S we estimate its abundance to be 9e-6 at 595 mb reducing to 7e-7 at 160 mb. While these figures are preliminary they are similar to previous determinations at sub-millimetre wavelengths and suggest increased abundances of phosphine near the pole. For ammonia, we find the profile to be close to saturation where our weighting functions peak at 450 mb, with an indication of increased ammonia to the south.

Work is ongoing to account for FOV-averaging effects and to improve the confidence of our estimates. These latest results will be presented.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.