Kirkwood belongs to the orbital Hilda group, which is located outermost part of the main belt.[4] Asteroids in this dynamical group have semi-major axis between 3.7 and 4.2 AU and stay in a 3:2 resonance with the gas giant Jupiter. Kirkwood, however, is a background asteroid and not a member of the (collisional) Hilda family (101).[5]
It orbits the Sun at a distance of 3.0–4.9 AU once every 7 years and 9 months (2,839 days). Its orbit has an eccentricity of 0.24 and an inclination of 1° with respect to the ecliptic.[1]
The asteroid was first observed as 1944 DF at Turku Observatory in February 1944. The body's observation arc begins with its observation as 1949 TF at Heidelberg Observatory in October 1949, fifteen months prior to its official discovery observation at Goethe Link.[3]
In October 2012, a rotational lightcurve of Kirkwood was obtained from photometric observations at the Etscorn Campus Observatory (719) in New Mexico, United States. Lightcurve analysis gave a rotation period of 12.518 hours with a brightness variation of 0.05 magnitude (U=2). Another lightcurve gave a period of 17.9 hours and an amplitude of 0.22 magnitude (U=2).[a]
Diameter and albedo
According to the surveys carried out by the Japanese Akari satellite, the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer and the Infrared Astronomical Satellite IRAS, Kirkwood measures between 47.077 and 57.14 kilometers in diameter and its surface has an albedo between 0.044 and 0.063.[6][7][8]
The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0517 and a diameter of 51.88 kilometers based on an absolute magnitude of 10.26.[4]
^ abSlyusarev (2012) web; for (1578) Kirkwood: rotation period of 17.9 hours with a brightness amplitude of 0.22 mag. Summary figures given at the LCDB
^Although the asteroid 1575 Winifred, also discovered by the Indiana Asteroid Program, has both a lower number and an earlier discovery date (20 April 1950) than 1578 Kirkwood
^ abcdUsui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. (online, AcuA catalog p. 153)