|Discovered by||E. F. Helin
Palomar Observatory (675)
|Discovery date||August 9, 1989|
|MPC designation||4769 Castalia (1989 PB)|
|Minor planet category||Apollo NEO,
|Epoch 14 march 2012
|Aphelion||1.5769 AU (Q)|
|Perihelion||0.54945 AU (q)|
|Semi-major axis||1.0631 AU (a)|
|Orbital period||1.10 yr|
|Mean anomaly||148.73° (M)|
|Longitude of ascending node||325.62°|
|Argument of perihelion||121.33°|
|Mass||5.0×1011 kg (?)|
|Mean density||2.1 g/cm³ (?)|
|Sidereal rotation period||4.095 h|
|Spectral type||S (?)|
|Absolute magnitude (H)||16.9|
The asteroid 4769 Castalia (// 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.
- "JPL Small-Body Database Browser: 4769 Castalia (1989 PB)". Jet Propulsion Laboratory. Retrieved 2012-06-17.
- "JPL Close-Approach Data: 4769 Castalia (1989 PB)". Retrieved 2012-06-17.
- "(4769) Castalia Ephemerides for August 1989". NEODyS (Near Earth Objects - Dynamic Site). Retrieved 2012-06-20.
- Mike Nolan (1996-05-15). "Radar image of 4769 Castalia". Arecibo Observatory. Retrieved 2012-06-19.
- NASA Asteroid Radar Search – The 228 Radar-Detected Asteroids: Asteroid 4769 Castalia