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Title:
Latitudinal Variations in Uranus' Near-Infrared Methane Absorption Bands
Authors:
Norwood, James; Chanover, N. J.
Affiliation:
AA(New Mexico State Univ.), AB(New Mexico State Univ.)
Publication:
American Astronomical Society, DPS meeting #39, #55.04; Bulletin of the American Astronomical Society, Vol. 39, p.526
Publication Date:
10/2007
Origin:
AAS
Bibliographic Code:
2007DPS....39.5504N

Abstract

As Uranus approaches its December 2007 equinox and observational technology improves, it has been documented that the Uranian disk does not appear completely uniform. Evident asymmetries include the southern hemisphere being brighter than the north (Hammel and Lockwood 2007, Icarus 186, 291-301), the lack of a northern polar collar (Hammel et al. 2005, Icarus 175, 534-545), and the distribution of cloud features (Sromovsky and Fry 2005, Icarus 179, 459-484). As Uranus' upper atmosphere is comprised of a haze layer of hydrocarbons above a methane cloud layer, these asymmetries may also indicate north-south variations in the methane abundance.

Near-infrared spectra of Uranus were acquired at NASA's Infrared Telescope Facility using SpeX (R = 2000) in September 2006 and September 2007. To take advantage of the favorable viewing geometry of Uranus at equinox, the spectrographic slit was oriented parallel to Uranus' equator to minimize the range of latitudes covered with each spectrum, thereby obtaining higher latitudinal resolution across the planet. By moving the slit across the Uranian disk from south to north in quarter-arcsecond increments, spectra were acquired for all latitudes. To investigate north-south variations in Uranus' near-infrared spectrum, pairs of spectra equidistant from Uranus' equator are compared here. By taking the ratios of these pairs of spectra, the relative strengths of Uranus' near-IR methane absorption bands are determined. Longitudinal variations are also investigated by comparing spectra taken at different times for each latitude.

This work was supported by NSF through award #AST-0507558, and the NASA Earth and Space Science Fellowship.

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