1866 Sisyphus

Lore & Background

1866 Sisyphus 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. The Apollo asteroid has an Earth minimum orbit intersection distance of 0.1037 AU (15,500,000 km), corresponding to 40.4 lunar distances. It 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 26 November 2071. When discovered it peaked at magnitude 9.0 on 25 November 1972. It is one of the brightest near-Earth asteroids. In the SMASS classification, Sisyphus is a common stony S-type asteroid. In 1985, it was detected with radar from the Arecibo Observatory at a distance of 0.25 AU, with a measured radar cross-section of 8 square kilometers. 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, and Brian Warner added additional weight to this conclusion, giving hours as the satellite's orbital period, longer than the 25 hours previously reported by Stephens.

Reader's Guide

1866 Sisyphus is notable as the largest member of the Apollo group of near-Earth asteroids, with a diameter comparable to the Chicxulub impactor. Its binary nature, discovered via radar in 1985 but only reported in 2007, adds to its scientific interest. The asteroid's orbit brings it relatively close to Earth, with a minimum orbit intersection distance of 0.1037 AU (15.5 million km), and it will make a notable approach in November 2071, reaching apparent magnitude 9.3. As one of the brightest near-Earth asteroids, it has been studied for its physical characteristics, including its stony S-type composition. Its naming after the mythological figure Sisyphus reflects the perpetual motion of its orbit. The asteroid's size and Earth-crossing status make it a significant object for understanding potential impact hazards, though the article does not classify it as an immediate threat. The discovery of its satellite and the subsequent refinement of the moon's orbital period highlight ongoing research into binary asteroid systems.

Did You Know?

• 1866 Sisyphus is the largest Earth-crossing asteroid, with a diameter comparable to the Chicxulub impactor.
• It was discovered on 5 December 1972 by Swiss astronomer Paul Wild at Zimmerwald Observatory.
• A small moon was detected around Sisyphus in 1985 via radar, but its existence was not reported until December 2007.
• The asteroid will pass 0.11581 AU from Earth on 24 November 2071, peaking at magnitude 9.3.