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Near Infrared Mapping Of Ceres Surface
Mauna Kea HI (SPX) Oct 12, 2006 Although Ceres is the largest main-belt asteroid and was the first to be discovered (by G.Piazzi in 1801), its physical properties are still not well understood. While it is expected to have retained a large amount of primordial water ice in its interior, many questions about the composition of its surface and sub-surface layers, the properties of its regolith, its degree of differentiation, etc, remain unanswered. We used state-of-the-art adaptive optics instrumentation available at the Keck observatory, Mauna Kea, Hawaii, to image the surface of Ceres with a spatial resolution of 30km. Our observations were carried out during the 2002 opposition of Ceres in the near-infrared J/H/K-bands, at a wavelength range particularly well adapted to investigate the composition and properties of planetary surfaces. We produced albedo maps covering 80% of the asteroid, which appears to display a wealth of 40 to 160km large geological features with intensity in reflected light varying by 12% across the surface (see attachment). We believe that these variations could be due to particular terrain features, as well as differences in their surface composition and/or degree of alteration by space weathering effects (ageing of surface due to interaction of solar wind, micrometeorites impacts, etc). We also derived measurements of the dimension and shape of Ceres, which can be considered as an oblate spheroid of radii a=481km and b=447km (incertitude of +/-14 km). The direction of its spin axis in a J2000 coordinate referential is right ascension=287 degrees and declination=69 degrees (5 degrees of incertitude). These two results are in agreements with earlier reports made by Thomas et al. (Nature 2005) from the analysis of Hubble Space Telescope observations. Additional spatially resolved spectroscopic observations are needed to investigate further the properties of Ceres surface. Such programs will help in the preparation of the NASA DAWN mission, which will reach Ceres in 2015 and explore, from orbit, the properties of this intriguing solar system body. We are currently planning complementary observations of Ceres during its next opposition of November 2007, using a suite of adaptive optics instruments at the Very Large Telescope of the European Southern Observatory in Chili. Related Links Division for Planetary Sciences, American Astronomical Society University of Wisconsin-Madison The Iron and Ice Of Our Solar System
Rosetta Performs Second Deep Space Manoeuvre
Paris, France (ESA) Oct 11, 2006This report covers a three week peroid of active cruise and was dedicated to the preparation and execution of the second Deep Space Manoeuvre (DSM2). The manoeuvre was executed on 29 September at 02:00 UTC. Its planned magnitude was 31.791 ms-1, which corresponds to an overall burn duration of about 52 minutes. |
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