|Discovered by||E. F. Helin
Palomar Observatory (675)
|Discovery date||9 August 1989|
|MPC designation||4769 Castalia (1989 PB)|
|Epoch 13 January 2016 (JD 2457400.5)|
|Uncertainty parameter 0|
|Observation arc||9467 days (25.92 yr)|
|Aphelion||1.5770 AU (235.92 Gm) (Q)|
|Perihelion||0.54957 AU (82.215 Gm) (q)|
|1.0633 AU (159.07 Gm) (a)|
|1.10 yr (400.46 d)|
|0° 53m 56.256s / day (n)|
|Known satellites||contact binary|
|Earth MOID||0.0199597 AU (2.98593 Gm)|
|Jupiter MOID||3.67272 AU (549.431 Gm)|
|Jupiter Tisserand parameter||5.676|
|Mass||5.0×1011 kg (?)|
|2.1 g/cm³ (?)|
|4.095 h (0.1706 d)|
Sidereal rotation period
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.
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.
- "JPL Small-Body Database Browser: 4769 Castalia (1989 PB)". Jet Propulsion Laboratory. Retrieved 14 April 2016.
- "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.
- Dr. Lance A. M. Benner (2013-11-18). "Binary and Ternary near-Earth Asteroids detected by radar". NASA/JPL Asteroid Radar Research. Retrieved 2014-03-01.