I. Seasonal Changes in Titan's Cloud Activity II. Volatile Ices on Outer Solar System Objects

Abstract

This thesis presents studies in two distinct areas of observational planetary astronomy: studies of Saturn's moon Titan's seasonally varying tropospheric clouds, and studies of the surface compositions of Kuiper belt objects. I. Understanding Titan's methane-based hydrological cycle and interpreting how and when the fluvial surface features seen by the Cassini Spacecraft were formed requires frequent long-term observations of Titan's clouds. Using nearly 100 adaptive optics images from the Keck and Gemini Telescopes from 2002-2006, we mapped the locations, frequencies, and magnitudes of Titan's clouds. We also developed a near-nightly cloud-monitoring program with the NASA Infrared Telescope Facility (IRTF). Nightly whole-disk infrared spectroscopy with IRTF allows us to determine Titan's total fractional cloud coverage, magnitudes, and altitudes, complementing and providing context for the relatively infrequent Cassini flybys. Taken together, the observations presented in this thesis have shown a striking seasonal change in the behavior of Titan's clouds as Titan has moved from southern summer solstice (October 2002) toward vernal equinox (August 2009) and indicate that seasonally varying insolation appears, to first order, to control Titan's cloud locations (Schaller et al. 2006a & 2006b). II. Unlike Pluto and Eris, the vast majority of Kuiper belt objects (KBOs) are too small and too hot to retain volatile ices like CH4, N2, and CO on their surfaces to the present day. As a result, their infrared spectra are either dominated by involatile water ice or dark spectrally featureless material. To understand the dichotomy between volatile-rich and volatile-free surfaces in the outer solar system, we constructed a model of atmospheric escape of volatile ices over the age of the solar system (Schaller & Brown 2007a). We predicted that Quaoar, an object about half the size of Pluto, should be just capable of retaining methane ice to the present day. We observed Quaoar with the Keck Telescope, used Hapke theory to model its spectrum, and found that it contains a small amount of methane on its surface, indicating that it is a transition object between the dominant volatile-poor small KBOs and the few volatile-rich KBOs such as Pluto and Eris (Schaller & Brown 2007b).