General Information
On 1989-Aug-25 Castalia passed 0.0269378 AU (4,029,840 km; 2,504,020 mi) (within eleven lunar distances) of Earth, allowing it to be observed with radar from the Arecibo Observatory by Scott Hudson (Washington State University) and Steven J. Ostro (JPL). The data allowed Hudson et al. to produce a three-dimensional model of the object. During the 1989 passage Castalia peaked at an apparent magnitude of 12.
Castalia has a peanut shape, suggesting two ~800-meter-diameter pieces held together by their weak mutual gravity. Since then radar observations of other asteroids have found other contact binaries.
Read more about this topic: 4769 Castalia
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