Mid-Infrared Ethane Emission on Neptune and Uranus
Abstract
We report 8-13 μm spectral observations of Neptune and Uranus from the NASA Infrared Telescope Facility spanning more than a decade. The spectroscopic data indicate a steady increase in Neptune's mean atmospheric 12 μm ethane emission from 1985 to 2003, followed by a slight decrease in 2004. The simplest explanation for the intensity variation is an increase in stratospheric effective temperature from 155+/-3 K in 1985 to 176+/-3 K in 2003 (an average rate of 1.2 K yr-1) and a subsequent decrease to 165+/-3 K in 2004. We also detected variation of the overall spectral structure of the ethane band, specifically an apparent absorption structure in the central portion of the band; this structure arises from coarse spectral sampling coupled with a nonuniform response function within the detector elements. We also report a probable direct detection of ethane emission on Uranus. The deduced peak mole fraction is approximately 1 order of magnitude higher than previous upper limits for Uranus. The model fit suggests an effective temperature of 114+/-3 K for the globally averaged stratosphere of Uranus, which is consistent with recent measurements indicative of seasonal variation.
Based on observations at the NASA Infrared Telescope Facility, operated by the University of Hawaii under contract to NASA. Some of the images shown herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA.- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2006
- DOI:
- 10.1086/503599
- arXiv:
- arXiv:astro-ph/0602546
- Bibcode:
- 2006ApJ...644.1326H
- Keywords:
-
- Infrared: Solar System;
- Planets and Satellites: Individual: Neptune;
- Planets and Satellites: Individual: Uranus;
- Astrophysics
- E-Print:
- Accepted for publication in ApJ. 16 pages, 10 figures, 2 tables