This S-type asteroid (composed of rocky silicates) orbits the Sun in the inner main-belt at a distance of 0.9–2.9AU 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.[1]
The Apollo asteroid has an Earth minimum orbit intersection distance of 0.1037AU (15,500,000km), which corresponds to 40.4 lunar distances.[1] It will pass 0.11581AU (17,325,000km) from Earth on 24 November 2071,[21] and will peak at roughly apparent magnitude 9.3 on 26 November 2071.[22] When it was discovered it peaked at magnitude 9.0 on 25 November 1972. It is one of the brightest near-Earth asteroids.
In 1985, this object was detected with radar from the Arecibo Observatory at a distance of 0.25AU. The measured radar cross-section was 8 square kilometers.[6][a] During the radar observations, a small minor-planet moon was detected around Sisyphus, although its existence was not reported until December 2007. Robert Stephens confirmed that it is a suspected binary,[7] and Brian Warner added additional weight to this conclusion, giving 27.16±0.05 hours as the satellite's orbital period, longer than the 25 hours previously reported by Stephens.[8]
Diameter and albedo
With a measured mean diameter in the range of 5.7–8.9 kilometers, it is the largest of the Earth-crossing asteroids, comparable in size to the Chicxulub object whose impact contributed to the extinction of the dinosaurs.[23] Larger near-Earth asteroids which are neither classified as Apollos nor Earth-crossers include 1036 Ganymed (32km), 3552 Don Quixote (19km), 433 Eros (17km), and 4954 Eric (10.8km).
