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B. A. Smith, R. Meier, T. C. Owen (IfA, UHawaii), E. Becklin (UCLA), R. J. Terrile (JPL)
We present images of the Jovian ring in three wide-band filters centered at 1.1, 1.6 and 2.05~\mum, using NICMOS (Near Infrared Camera and Multi-Object Spectrograph), a cryogenically-cooled, second-generation, near-IR instrument aboard HST (Hubble Space Telescope). All exposures were obtained during a single HST orbit on 28 October 1997 when the Earth was very close to the Jovian ring plane, such that the dust ring appeared edge-on and the column-integrated flux of the optically-thin ring was maximized. The near-infrared spectral reflectance of the Jupiter dust ring is poorly known from groundbased observations because of problems with scattered light from the planet. NICMOS has important advantages over groundbased observations, such as low sky background, freedom from atmospheric scattering, and a baffle system that efficiently suppresses instrumentally scattered light. We were careful to place Jupiter just outside the field of view and to avoid its bright satellites. In turn we used Adrastea, the fainter of the two known satellites orbiting within the dust ring, as a calibration reference throughout the observations. Highly accurate photometry of the ring and Adrastea indicates that both are unusually red objects. Modeling of the radial flux distribution leads to the radially dependent surface density of the ring particles. To identify the source and nature of the ring material, we compare the photometric properties of the ring with those of Adrastea, Metis, Amalthea and Io.