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The Fuzzy Face Of Ceres

SKY & TELESCOPE'S NEWS BULLETIN - October 12, 2001

THE FUZZY FACE OF CERES

When Guiseppe Piazzi discovered Ceres on January 1, 1801, he believed he'd found the planet hypothesized to orbit between Mars and Jupiter. Although Ceres is no planet, it turned out to be the largest body in the asteroid belt. And now, two centuries later, astronomers finally have a crude idea of what its surface looks like.

Thanks to the optical prowess of the Hubble Space Telescope, a team of observers led by Joel W. Parker (Southwest Research Institute) captured several images of Ceres on June 25, 1995, in ultraviolet light (at which HST affords the best resolution). Previous ground-based observations had resolved Ceres' disk, but only crudely, using adaptive optics; by contrast, Hubble's images reveal details as small as 50 kilometers across. Apparently the side of Ceres recorded by HST is rather bland, except for one dusky dark marking about 250 km across. As Parker and his colleagues describe in the forthcoming January 2002 issue of the Astronomical Journal, it's unclear whether this spot is a crater, a dark area, or something else. But they believe it's a real feature, enough so to propose that it be named Piazzi.

The 5-hour HST run was not long enough to follow Ceres through an entire 9.1-hour rotation, but the pictorial coverage suggests a mean diameter of 950 8 km. From that, as well as previous mass estimates, the team determined that Ceres' mean density is roughly 2.6 g/cm^3 -- a reasonable match to the rocky, carbon-enriched composition suggested by the asteroid's spectrum. Ceres occupies a roughly circular orbit that averages 2.8 astronomical units (414 million km) from the Sun.


Copyright 2001 Sky Publishing Corporation. S&T's Weekly News Bulletin and Sky at a Glance stargazing calendar are provided as a service to the astronomical community by the editors of SKY & TELESCOPE magazine. Widespread electronic distribution is encouraged as long as these paragraphs are included. But the text of the bulletin and calendar may not be published in any other form without permission from Sky Publishing (contact permissions@skypub.com or phone 617-864-7360). Updates of astronomical news, including active links to related Internet resources, are available via SKY & TELESCOPE's site on the World Wide Web at http://www.skypub.com/.

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