|Discovery date 9 August 1989|
Orbital period 402 days
Named after Castalia
|Observation arc 9467 days (25.92 yr)|
Discovered 9 August 1989
Discoverer Eleanor F. Helin
Discovery site Palomar Observatory
|Discovered by E. F. Helin
Palomar Observatory (675)|
MPC designation 4769 Castalia (1989 PB)
Minor planet category Apollo NEO, PHA Venus-crosser asteroid, Mars-crosser asteroid
Aphelion 1.5770 AU (235.92 Gm) (Q)
Similar 2101 Adonis, 54509 YORP, 9969 Braille, 588 Achilles, 1862 Apollo
The asteroid 4769 Castalia (/kəˈsteɪliə/ kə-STAY-lee-ə; previously known by the provisional designation 1989 PB) was the first asteroid to be modeled by radar imaging. 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.
On 25 August 1989 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 approximately 800-meter-diameter pieces held together by their weak mutual gravity. Since then radar observations of other asteroids have found other contact binaries.
Castalia is a potentially hazardous asteroid (PHA) because its minimum orbit intersection distance (MOID) is less than 0.05 AU and its diameter is greater than 150 meters. The Earth-MOID is 0.0204 AU (3,050,000 km; 1,900,000 mi). Its orbit is well-determined for the next several hundred years.