Discovered by H. E. Holt MPC designation 9175 Graun Orbits Sun Asteroid group Asteroid belt | Discovery date 29 July 1990 Discovered 29 July 1990 | |
Named after Ken Graun(author, astronomy) Alternative names 1990 OO2 · 1975 CL1980 BB1 · 1986 WS41991 XL2 Similar Sun, 170 Maria, 714 Ulula, 695 Bella | ||
9175 Graun, provisional designation 1990 OO2, is an asteroid from the middle region of the asteroid belt, approximately 10 kilometers in diameter. It was discovered by American astronomer Henry E. Holt at the U.S. Palomar Observatory in California, on 29 July 1990.
The Collaborative Asteroid Lightcurve Link (CALL) classifies the asteroid as a member of the Eunomia family, a large group of S-type asteroids and the most prominent family in the intermediate main-belt, while, based on its concurring orbital elements, Alvarez-Candal from the Universidad Nacional de Córdoba and others, group the asteroid into the Maria family, which is named after its namesake, the asteroid 170 Maria. It is an old-type asteroid family, about 7009300000000000000♠(3±1)×109 years old, located near the area of a 3:1 resonances with Jupiter that supplies near-Earth asteroids to the inner Solar System (also see Kirkwood gap). It is estimated that every 100 million years, about 37 to 75 Maria asteroids larger than 1 kilometer become near-Earth objects.
The stony asteroid orbits the Sun at a distance of 2.2–3.0 AU once every 4 years and 2 months (1,532 days). Its orbit has an eccentricity of 0.14 and an inclination of 15° with respect to the ecliptic. The first observation was made at the Karl Schwarzschild Observatory in 1975, extending the asteroid's observation arc by 15 years prior to its discovery.
In January 2013, a rotational light-curve for this asteroid was obtained from photometric observations taken at Korean and other observatories. It rendered a rotation period of 7001258000000000000♠25.8±0.5 hours with a brightness variation of 0.16 in magnitude (U=2+). The measurement supersedes a previous observation from South America that gave a shorter period of 20 hours and an amplitude of 0.2 in magnitude (U=1).
According to the surveys carried out by the Japanese Akari satellite and NASA's Wide-field Infrared Survey Explorer (WISE) with its subsequent NEOWISE mission, the asteroid measures 10.4 and 7.9 kilometers, respectively. The discrepancy in the determined diameters is due to a divergent measurement of the asteroid's albedo, as the higher a body's reflectivity (albedo) the lower its diameter, for a given absolute brightness (magnitude). While WISE finds a very high albedo of 0.31, results from the Akari satellite gave a relatively low albedo of 0.18. Moreover, CALL assumes an intermediate albedo of 0.21, a typical value for stony asteroids, and calculates a diameter of 10.5 kilometers.
The minor planet was named in honor of American amateur astronomer and publisher, Ken Graun (b. 1955), author of two books on astronomy, owner of "Ken Press" and the website What's Out tonight?, bringing astronomy to the broader public including children. Naming citation was published on 9 March 2001 (M.P.C. 42358).