Discovered by P. Wild MPC designation 1866 Sisyphus Alternative names 1972 XA Aphelion 2.91 m Discoverer Paul Wild | Discovery date 5 December 1972 Pronunciation /ˈsɪsᵻfəs/ (SIS-i-fəs) Discovered 5 December 1972 Orbits Sun Discovery site Zimmerwald Observatory | |
Minor planet category Apollo · NEO · Mars-crosser Named after Sisyphus (Greek mythology) Similar 1685 Toro, 1865 Cerberus, 4183 Cuno, 2063 Bacchus, 1862 Apollo | ||
1866 Sisyphus (SIS-i-fəs), provisional designation 1972 XA, is a binary stony asteroid, near-Earth object and the largest member of the Apollo group of asteroids, approximately 7 kilometers in diameter. It was discovered on 5 December 1972, by astronomer Paul Wild at Zimmerwald Observatory near Bern, Switzerland.
This S-type asteroid (composed of rocky silicates) orbits the Sun at a distance of 0.9–2.9 AU once every 2 years and 7 months (952 days). Its orbit has an eccentricity of 0.54 and an inclination of 41° with respect to the ecliptic. Sisyphus has an Earth minimum orbit intersection distance of 0.1036 AU (15,500,000 km), which corresponds to 40.4 lunar distances.
In 1985, this object was detected with radar from the Arecibo Observatory at a distance of 0.25 AU. The measured radar cross-section was 8 square kilometers. During the radar observations, a small satellite was detected around Sisyphus, although its existence was not reported until December 2007. Stephens confirmed that it is a suspected binary, and Brian D. Warner added additional weight to this conclusion, giving 7001271600000000000♠27.16±0.05 hours as the satellite's orbital period, longer than the 25 hours previously reported by Stephens.
Sisyphus will pass 0.11581 AU (17,325,000 km) from Earth on 24 November 2071, and will peak at roughly apparent magnitude 9.3 on November 26, 2071. When it was discovered it peaked at magnitude 9.0 on 25 November 1972. It is one of the brightest near-Earth asteroids. With a measured mean diameter in the range of 5.7–8.9 kilometers, it the largest of the Earth-crossing asteroids, comparable in size to the Chicxulub object whose impact contributed to the extinction of the dinosaurs. Larger near-Earth asteroids which are neither classified as Apollos nor Earth-crossers include 1036 Ganymed (32 km), 3552 Don Quixote (19 km), 433 Eros (17 km), and 4954 Eric (10.8 km).
The minor planet is named after the Sisyphus from Greek mythology and refers to the cruel king of Ephyra, punished by being given the task of rolling a large stone up to a hill in the underworld, only to have it roll down again each time he neared the top. Naming citation was published before November 1977 (M.P.C. 3758).