4769 Castalia
The asteroid 4769 Castalia (previously known by the provisional designation 1989 PB) was the first asteroid to be directly imaged. It is an Apollo, Mars- and Venus-crosser asteroid. It was discovered on August 9, 1989 by Eleanor F. Helin (Caltech) on photographic plates taken at Palomar Observatory. It is named after Castalia, a nymph in Greek mythology.
General information
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.
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