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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[10.02] Neptune's Ethane Abundance and Uranus' Lack Thereof

H. B. Hammel (Space Sci. Inst.), D. K. Lynch, R. W. Russell (Aerospace Corp.), M. L. Sitko (U. Cinc.), E. Polomski (U. Minn.)

As the 2007 equinox of Uranus nears, several lines of evidence suggest that the planet's atmosphere may be undergoing detectable changes as a result of redistribution of insolation from the southern to the northern hemisphere. The data include HST and ground-based images, visible and near-IR photometry, and ISO measurements of hydrocarbon abundances. This latter observation in particular led us to attempt to measure the strength of Uranus' 12.2-micron ethane band with The Aerospace Corporation's Broadband Array Spectrograph System (BASS: 3-13.5 microns) on the NASA IRTF. We also remeasured this ethane band on Neptune to compare with similar observations made with the same instrument eleven years earlier (Hammel et al. 1992, Icarus 99, 347).

We observed Uranus and Neptune with IRTF/BASS from 26 July to 1 August 2002 UT. For the observations, Neptune's 2.4-arcsec disk and Uranus' 3.7-arcsec disk were centered in the BASS 3.8-arcsec beam. Uranus was very faint, but was detected in the 8-13.5 micron window. From the observations, we will be able to place an integrated (over the band) upper limit on stratospheric ethane on Uranus. As in the past, Neptune exhibited strong ethane emission at 12.2 microns and methane emission near 8 microns, with abundances similar to those seen in 1991. We observed Neptune several times each night; thus we will be able to assess rotational modulation of the emission.

This work was supported in part by NASA grants NAG5-10451 and NAG5-9475. DKL and RWR acknowledge The Aerospace Corporation's Independent Research and Development program, and the USAF Space and Missile Systems Center through the Mission Oriented Investigation and Experimentation program (contract F4701-00-C-0009). The authors were visiting astronomers at the IRTF, operated by U. Hawaii under contract from NASA.

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