4769 Castalia

4769 Castalia

Orbital characteristics
Orbit type	Near-Earth
Semimajor axis	1.063 AU
Eccentricity	0.4831
Orbital period	1.10 years
Inclination	8.89°
Physical characteristics
Diameter	1.8×0.8 km
Mass	5.0×1011 kg
Density	2.1 g/cm3
Rotation period	4h
Spectral class	S[?]
Albedo	?
History
Discoverer	Eleanor F. Helin[?], 1989

The asteroid Castalia was the first asteroid to be directly imaged, in August of 1989. Its orbit took it within 11 lunar distances of Earth, allowing it to be scanned with radar from the Arecibo radio telescope.

Castalia was found to have a peanut shape, suggesting two 800m 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.