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C. Dumas, R. J. Terrile (JPL/Caltech), B. A. Smith (Univ. Hawaii), G. Schneider (Univ. Arizona), E. E. Becklin (UCLA)
Until recently, the system of Neptune's inner satellites and ring-arcs had only been observed in direct imaging from the Voyager~2 spacecraft, limiting our knowledge of this system to visible wavelengths data. Nearly ten years after the Voyager fly-by, HST/NICMOS observed the close vicinity of Neptune at 1.87\mum, a wavelength that corresponds to a strong methane absorption in the atmosphere of Neptune and allows the attenuation of the scattered light produced by the planet. We derived the near-infrared geometric albedo of the ring-arcs and small moons Proteus, Larissa, Galatea and Despina, and compared their orbital positions with the predictions from the 1989 Voyager observations. The surfaces of the inner satellites of Neptune appear to be coated with dark, neutral material, with albedoes ranging from 0.077 (Proteus) to 0.033 (Despina) and their orbital position was found to be within the prediction errors of the Voyager measurements. The material located inside the ring-arcs of Neptune also displays a low-neutral reflectance (p1.87 \mu m ~0.055) and the HST/NICMOS measurement of the mean orbital motion of the ring-arcs shows that their confinement cannot be entirely explained by resonances produced by the nearby satellite Galatea (Nature, 400, 733-735).
This work was performed at the Jet Propulsion Laboratory, Caltech, under contract with the National Aeronautics and Space Administration, and is supported by NASA grant NAG5-3042.
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The author(s) of this abstract have provided an email address for comments about the abstract: Christophe.Dumas@jpl.nasa.gov