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I. de Pater (UC Berkeley), S.G. Gibbard (IGPP/LLNL), H.B. Hammel (SSI)
We have observed Uranus with the Keck Adaptive Optics system since June 2000. Our best (and most recent) images are at ring inclination angles of 18 deg (Oct. 2003) and 11 deg. (July 2004). The peri-apogee asymmetry of the epsilon ring increases from q=3.2 to q~3.6 in these observations, in agreement with Karkoschka's predictions (2001, Icarus 151, 78). In these images the three groups of rings interior to the \epsilon ring are prominent features, and are clearly resolved. As the apparent inclination of the rings decreases from 18 to 11 deg, sheets of dust in the uranian ring system become more visible (ring plane crossing is in 2007). Images in July 2004 reveal a broad sheet of material inside the main ring system, clearly displaced from ring 456. We identify this as the ring 1986U2R, last seen during the 1986 Voyager flyby. This sheet of material is visible between ~35000 and ~41000 km from the center of the planet, peaking in intensity at ~39000 km. When modeled as a flat sheet of material of uniform density, it is ~2000 km wide, centered at a uranian distance 39340 km, with an I/F about 50 times less than that of the brightest inner rings (e.g., \alpha and \beta). Hammel et al. (see abstract this volume) discuss cloud features in Uranus's atmosphere seen in these images.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.