It was discovered on 5 December 1972, by Swiss astronomer
Paul Wild at
Zimmerwald Observatory near Bern, Switzerland, and given the provisional designation 1972 XA. It was named after
Sisyphus from Greek mythology.[3][20]
Orbit and classification
This
S-type asteroid (composed of rocky silicates) orbits the Sun in the
inner main-belt 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.[1]
The Apollo asteroid has an Earth
minimum orbit intersection distance of 0.1037
AU (15,500,000
km), which corresponds to 40.4
lunar distances.[1] It will pass 0.11581 AU (17,325,000 km) 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 0.25 AU. 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 (32 km),
3552 Don Quixote (19 km),
433 Eros (17 km), and
4954 Eric (10.8 km).
^Schmadel, Lutz D. "Appendix – Publication Dates of the MPCs". Dictionary of Minor Planet Names – Addendum to Fifth Edition (2006–2008). Springer Berlin Heidelberg. p. 221.
doi:
10.1007/978-3-642-01965-4.
ISBN978-3-642-01964-7.