4769 Castalia
 A 3D model of the different faces of Castalia. Image by AAAS | |
| Orbital characteristics | |
|---|---|
| Orbit type | Near-Earth |
| Semimajor axis | AU |
| Eccentricity | 0.4831 |
| Orbital period | 1.10 year |
| Inclination | 8.89° |
| Physical characteristics | |
| Diameter | km |
| Mass | 11 kilogram>kg |
| Density | 2.1 g/cm3 |
| Rotation period | 4 h |
| Spectral class | S |
| Albedo | ? |
| History | |
| Discoverer | E. F. Helin, 1989 |
The asteroid 4769 Castalia (previous known only by the provisional designation 1989 PB) was the first asteroid to be directly imaged. It was discovered on August 9, 1989 by Eleanor F. Helin (Caltech) on photographic plates taken on Palomar Observatory. It is named after Castalia, a nymph in Greek mythology.
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Castalia's orbit took it within 11 lunar distances of Earth, allowing it to be scanned with radar from the Arecibo Observatory by Scott Hudson (Washington State University) and Steven J. Ostro (JPL). The obtained data allowed astronomers to produce a three-dimensional computer model of it.
Castalia was found to have a peanut shape, suggesting two 800 m diameter pieces held together by their weak mutual gravity. Since then radar measurements of other asteroids has indicated that this contact binary arrangement appears to be common.General information