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Posted by baalke on October 16, 2006, 12:37 pm
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http://www.keckobservatory.org/article.php?id=93
Images of Dwarf Planet Ceres
Keck Observatory
Pasadena, Calif. (October 11th, 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 and its degree of
differentiation, remain unanswered.
A team of astronomers led by Benoit Carry of the Paris-Meudon
Observatory 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. The observations
were carried out during the September 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. The team produced albedo maps covering 80 percent of the
asteroid, which appears to display a wealth of 40 to 160km large
geological features with intensity in reflected light varying by ~12
percent across the surface. The team suggests that the variations could
be due to terrain features, as well as differences in their surface
composition and/or degree of alteration by space weathering effects
(such as aging of surface due to interaction of solar wind,
micrometeorites impacts, etc).
The team also derived measurements of the dimension and shape of the
dwarf planet 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. The team is currently planning complementary observations
of Ceres during its next opposition in November 2007, using a suite of
adaptive optics instruments at the Very Large Telescope of the European
Southern Observatory in Chili.
Press Release Courtesy: AAS Division of Planetary Sciences
Media Contact:
Laura K. Kinoshita
W. M. Keck Observatory
65-1120 Mamalahoa Hwy.
Kamuela, HI 96743
(808) 885-7887
newsletter@keck.hawaii.edu
[Images]
http://www.keckobservatory.org/images/article_pictures/93_224.jpg
Credit: LESIA\ESO\SwRI\W. M. Keck Observatory
Infrared images of Ceres reveal a textured surface, and astronomers
have
produced a colour 3D model from the data. The blue in the 3D model
corresponds to the dark patches in the infrared, the yellow to the
bright. The blackout at the edges is due to insufficient data at the
poles.
Credit: LESIA\ESO\SwRI\W. M. Keck Observatory
360 images from the NIRC2 camera on Keck II were used to produce this
infrared image of Ceres.
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