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M. R. Showalter (Stanford), J. J. Lissauer (NASA Ames)
We have obtained a series of very deep exposures of the Uranian ring-moon system using the High Resolution Channel (HRC) of the Advanced Camera for Surveys on the Hubble Space Telescope. Exposures are very long (240 seconds) and use the broad clear filter to maximize the signal-to-noise ratio obtained. The planet is vastly over-exposed but the camera is oriented so that saturated pixels bloom parallel to Uranus's pole and so do not interfere with the rings and moons to each side.
In August 2003 we obtained 24 images during three consecutive orbits of HST, spanning a period of ~~4 hours. In August 2004 we carried out two repeat visits, each consisting of 40 images (five orbits of HST, ~~7 hours duration) and separated by 6.8 days. Initial observations resulted in the recovery of two satellites, Ophelia and S/1986~U~10 (IAU Circular #8192), and the discovery of two more, S/2003~U~1 and S/2003~U~2 (IAU Circular #8209). S/2003~U~1 orbits near semimajor axis 97,730 km, between Puck and Miranda. S/2003~U~2 orbits near 74,800 km, just interior to Belinda. We will report on the combined analysis of all these observations, which will enable us to further refine the orbits of the inner Uranian moons.
Images of the inner ring system have been processed by subtracting a median frame from each individual image; this eliminates the strong gradient of scattered light from the planet. Subtracted frames show a host of arc-like features orbiting within the ring system. Most of these are located in Ring~\epsilon and represent subtle variations in reflectivity or width. The dynamics of these features will also be discussed.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.