36th DPS Meeting, 8-12 November 2004
Session 28 Asteroid Physical Properties I
Oral, Thursday, November 11, 2004, 10:30am-12:00noon, Clark

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[28.01] Ceres Observations with HST: First Results

J. Wm. Parker (Southwest Research Institute), P. Thomas (Cornell University), E. Young (Southwest Research Institute), M. R. Sykes (Planetary Science Institute), L. A. McFadden (University of Maryland), C. T. Russell (University of California), S. A. Stern (Southwest Research Institute)

Our team has obtained 259 images of Ceres using the High Resolution Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. These images were obtained at high temporal sampling in three filter bands (V, U, and mid-UV) over the entire rotational phase of Ceres. The resolution was 30 km/pixel, allowing us to detect and follow the motions of surface features on Ceres for the first time. Light and dark patches are seen on the surface, with high contrast and differences among the three filters. A strong feature near the equator provided a control point to finally definitively determine the rotational pole of Ceres: RA=291 deg and Dec=59 deg. Based on limb fits to an accuracy of nearly 0.1 pixel, our shape measurements show that Ceres is rotationally symmetric with an equatorial radius of 487.3 km and a polar radius of 454.7 km with roughly 5 km uncertainties. This flattening is significantly less than expected for a relaxed body of Ceres' mean density and rotation period, but it is consistent with such a body if Ceres has a central rocky core surrounded by water ice.

Support for this project is through STScI grant HST-GO-09748.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.