AAS 197, January 2001
Session 64. Science with Adaptive Optics
Special Session Oral, Tuesday, January 9, 2001, 1:30-3:00pm, San Diego

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[64.03] The Solar System Up Close: AO Spectroscopy from Palomar

M.E. Brown (Caltech)

Solar system objects make natural targets for AO systems. Many are bright enough to use as a natural guide star and large enough to be resolved at the diffraction limit. For many systems, solar system objects have proved an invaluable early test of the capabilities of the system.

The Palomar AO system was the first to go on-line with a diffraction-limited spectrograph; for the reasons above, most of the early work with this spectrograph has been on objects in the solar system. We will briefly describe observations of several solar system objects obtained over the past 18 months, but we will concentrate on recent observations of Saturn's satellite Titan.

Titan is the largest moon in the solar system and is covered with an atmosphere thicker than that of the earth. The atmosphere is opaque at visible wavelengths owing to scattering from abundant hydrocarbon hazes; at infrared wavelengths the surface of the satellite is murky but ultimately visible. Past high resolution observations from HST imaging, speckle imaging, and, more recently, AO imaging have shown consistent albedo variations on the surface of the satellite, possibly corresponding to topographic variations or to continents surrounded by ethane lakes or oceans, but all of these past observations have relied on uncertain modeling of the variable atmospheric extinction to try to extract conditions at the surface. Using the Palomar AO spectrograph, we obtained a data cube of spectra at each diffraction limited point on the satellite. With the spectra, we construct highly constrained atmospheric models at each point and extract complete information on the atmospheric structure and surface spectrum. The spectra show that some of the bright spots seen at Titan are haze or cloud layers higher in the atmosphere while some are truly features at ground layer. We will use the extracted spectral information to suggest the composition of the materials on the surface of Titan, the distribution of ethane lakes and oceans, and what the Huygens probe will see when it hits the surface of this satellite.

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