The Methane Abundance and Structure of Cloud Bands on Uranus.

Details The Methane Abundance and Structure of Cloud Bands on Uranus. The Methane Abundance and Structure of Cloud Bands on Uranus.

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.0904s&link_type=abstract

American Astronomical Society, DPS meeting #39, #9.04; Bulletin of the American Astronomical Society, Vol. 39, p.424

Physics

Optics

Scientific paper

Grism spectra of Uranus obtained in October 2006 using the Keck II telescope and NIRC2 instrument with adaptive optics provide constraints on the methane mixing ratio and vertical cloud structure. The best model fits to central meridian spectral features in the H band (1.49-1.635 microns) are obtained with methane volume mixing ratio of 1.0+/-0.25 percent near a latitude of 43 S, and 1-1.6 percent for latitudes near 12 S and 33 N. The implications of the J-band spectra are confused by large differences between the short-wavelength and long-wavelength sides of the 1.28-micron window. The short-wavelength side (1.23-1.3 microns) is best fit with 1.6 percent CH4, but if the entire band is included (1.2-1.34 microns) the best fit CH4 mixing ratio is 4 percent or more, although many small scale spectral features are poorly fit over this range even at high methane mixing ratios, suggesting that methane absorption models in this band may not be as well characterized. Most of the latitudinal variability in the H band spectra can be fit with clouds near 2 bars and 6-8 bars, with cloud reflectivity of the deeper layer increasing from 2 percent at 33 N to 3-4 percent in the southern hemisphere, and that of the upper layer from 0.5 percent to 1 percent from 33 N to the bright band centered near 43 S. The bright band is also associated with a lowering of the deep cloud pressure by about 1.4 bars. The lack of significant cloud reflectivity near the 1.2-bar methane condensation level is confirmed by narrow-band imaging observations using both Keck and HST.
This research was supported by NASA Planetary Astronomy and Planetary Atmospheres programs.

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