4769 Castalia

4769 Castalia (/kəˈsteɪliə/; prov. designation: 1989 PB) is a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.4 kilometers (0.87 miles) in diameter and was the first asteroid to be modeled by radar imaging. It was discovered on 9 August 1989, by American astronomer Eleanor Helin (Caltech) on photographic plates taken at Palomar Observatory in California. It is named after Castalia, a nymph in Greek mythology. It is also a Mars- and Venus-crosser asteroid.[1]

4769 Castalia
Arecibo radar image showing Castalia as a contact binary
Discovery[1]
Discovered byE. F. Helin
Palomar Observatory (675)
Discovery date9 August 1989
Designations
(4769) Castalia
Pronunciation/kæˈsteɪliə/[2]
Named after
Castalia
1989 PB
Orbital characteristics[1]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 0
Observation arc9467 days (25.92 yr)
Aphelion1.5770 AU (235.92 Gm)
Perihelion0.54957 AU (82.215 Gm)
1.0633 AU (159.07 Gm)
Eccentricity0.48313 (e)
1.10 yr (400.46 d)
327.23°
0° 53m 56.256s / day
Inclination8.8863°
325.59°
121.35°
Known satellites1 contact binary
Earth MOID0.0199 AU (7.7 LD)[1]
Physical characteristics
Mean diameter
  • 1.4 km[1]
  • 1.8×0.8 km
4.095 h (0.1706 d)[1]
16.9[1]

    General information

    On 25 August 1989 Castalia passed 0.0269378 AU (4,029,840 km; 2,504,020 mi)[3] (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.[4]

    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.[5]

    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).[1] Its orbit is well-determined for the next several hundred years.

    Earth Approach on 22 August 2023[1]
    Date JPL Horizons
    nominal geocentric
    distance (AU)    		 uncertainty
    region
    (3-sigma)
    2023-Aug-22 09:210.11003 AU (16.460 million km)[1]±6 km[6]

    See also

    References
    1. "JPL Small-Body Database Browser: 4769 Castalia (1989 PB)". Jet Propulsion Laboratory. Retrieved 14 April 2016.
    2. "Castalia". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
    3. "JPL Close-Approach Data: 4769 Castalia (1989 PB)". Retrieved 17 June 2012.
    4. "(4769) Castalia Ephemerides for August 1989". NEODyS (Near Earth Objects – Dynamic Site). Retrieved 20 June 2012.
    5. Lance A. M. Benner (18 November 2013). "Binary and Ternary near-Earth Asteroids detected by radar". NASA/JPL Asteroid Radar Research. Archived from the original on 8 June 2004. Retrieved 1 March 2014.
    6. "Horizons Batch for 2023-08-22 Close Approach". JPL Horizons. Archived from the original on 26 October 2022. Retrieved 26 October 2022. RNG_3sigma = uncertainty range in km. (JPL#95/Soln.date: 2022-Jul-11 generates RNG_3sigma = 5.8 km)
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