Physics – Optics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt........20r&link_type=abstract
Thesis (PhD). UNIVERSITY OF CALIFORNIA, BERKELEY, Source DAI-B 64/02, p. 765, Aug 2003, 187 pages.
Physics
Optics
6
Scientific paper
Titan stands out in our solar system as the sole moon with a substantial atmosphere. Until recently the only spatially resolved observations of Titan were from the Voyager spacecraft flybys in 1980 and 1981 when the season was early northern spring on Titan. The advent of large ground-based telescopes and adaptive optics allow us to study Titan and its atmosphere with spatial resolutions of a few hundred kilometers. We report near- and mid-infrared observations of Titan's atmosphere with the W. M. Keck and Gemini telescopes in late southern spring on Titan. These observations represent the start of a long-term ground-based monitoring campaign that will extend over a significant fraction of Titan's 30-earth year seasonal cycle, and in doing so will lead us to a better understanding of the seasonal variations. Observing at mid-infrared wavelengths (8 13 μm) with the Long-Wavelength Spectrometer (LWS) on the W. M. Keck I Telescope we found a large build up of ethylene (C2H4) in the south polar stratosphere. We link this buildup to chemistry that occurs in the shadow of the winter pole. We also developed a new line-by-line radiative transfer model for Titan at 8 13 μm. This model can easily be extended to longer wavelengths, and will in the future be useful for several Titan-related projects, including long-term monitoring of south polar ethylene. At near-infrared wavelengths (1 2.5 μm) using adaptive optics on the W. M. Keck II Telescope we found a collar of haze near the tropopause at 70 75°S latitude. This collar is most likely the remnant of stratospheric nitrile chemistry during the long polar winter night. We report the first spatially resolved detection of clouds on Titan. These observations were made using adaptive optics on the Gemini North and W. M. Keck II telescopes. We found the discrete cloud features to vary on the timescales of hours to days. All clouds were near the south pole, with the most northern cloud appearing at 61°S. We find each cloud covers an area of Titan's surface of 2 × 104 km 2 to 3 × 105 km2. From a limited temporal sample these clouds appear to be common in the south polar region in late southern spring. We discuss several possible seasonal triggering mechanisms for these clouds. Finally, in appendices we present a new telluric transmission model and discuss the implications of differential atmospheric refraction for adaptive optics observations.
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