DPS 34th Meeting, October 2002
Session 10. Outer Planet Chemistry and Thermal Structure
Oral, Chair(s): G. Schubert and H. Hammel, Monday, October 7, 2002, 5:00-6:00pm, Room M

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[10.05] A New Infrared Heterodyne Search for Ethane in the Stratosphere of Uranus

T. A. Livengood (Challenger Ctr), H. B. Hammel (Space Sci. Inst.), Th. Kostiuk, J. N. Annen, K. E. Fast (NASA's GSFC), T. Hewagama (U. of MD), F. Schmülling (U. Cologne, Germany), D. Buhl (NASA's GSFC)

Observations of Uranus were obtained on August 1314, 2002 at the NASA Infrared Telescope Facility using the GSFC Heterodyne Instrument for Planetary Winds and Composition (HIPWAC) to search for the spectroscopic signature of stratospheric ethane (C2H6) at 11.89~\mum. These observations were aimed to characterize the current abundance of this trace species to investigate the stratosphere's seasonal development. Previous attempts to measure ethane concentration in Uranus were marginal at best due to Uranus' low stratospheric temperatures and hydrocarbon photochemical product abundances. However, Uranus' appearance is changing as it approaches its 2007 equinox: Hubble Space Telescope images show latitudinal (zonal) banding and discrete features with high near-IR contrast (Karkoschka, Science 280, 570572, 1998). Disk-integrated visible and near-IR photometry also suggest aerosol structure variability, leading to the suggestion that hydrocarbon abundances may vary significantly as insolation changes from southern summer to southern autumn. This general speculation is supported by the specific result that ISO-derived measurements of acetylene concentration significantly exceed Voyager derivations (Encrenaz et al., Astron.\ and Astrophys. 333, L43L46, 1998). We will report on the results of the IRTF spectroscopic effort and compare present results with marginal and upper limit determinations of ethane concentration in the stratosphere of Uranus (e.g., BASS 12.2 ~\mum spectroscopy, Hammel et al., this meeting).

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.