617 PATROCLUS

'617 Patroclus' is a binary minor planet made up of two similarly-sized objects orbiting their common centre of gravity. It is classified as a Trojan, sharing an orbit with Jupiter. It was discovered in 1907 by August Kopff, and was the second Trojan asteroid to be discovered. Recent evidence suggests that the objects are icy comets, rather than rocky asteroids.

Contents

Orbit

Binary

Composition

See also

Notes

External links

Orbit

Patroclus orbits in Jupiter's trailing Lagrangian point, L₅, in an orbit called the 'Trojan node' after one of the sides in the legendary Trojan War (the other node is called the 'Greek node'). Patroclus is the only object in the Trojan camp to be named after a Greek character; the naming conventions for the Trojan asteroids were not adopted until after Patroclus was named (similarly, the asteroid Hektor is the only Trojan character to appear in the Greek camp).

Binary

In 2001, it was discovered that Patroclus is a binary object, made up of two components of roughly similar size. In February, 2006, a team of astronomers led by Franck Marchis measured accurately the orbit of the system using the Keck Laser guide star adaptive optics system. They estimated that the two components orbit around their center of mass in 4.283±0.004 d at a distance of 680±20 km, describing a roughly circular orbit. Combining their observations with thermal measurements taken in November 2000, the team estimated the size of the components of the system. The slightly larger component, which measures 122 km in diameter, retains the name Patroclus. The smaller component, measuring 112 km, is now named 'Menoetius ' (full name '(617) Patroclus I Menoetius'), after the legendary Patroclus's father. Its provisional designation was 'S/2001 (617) 1'.

Composition

Because of the density of the components (0.8 g/cm³) is less than water and about one third that of rock, the team of researchers led by F. Marchis suggest that the Patroclus system, previously thought to be a pair of rocky asteroids, is more similar to a comet in composition. It is suspected that many Trojan asteroids are in fact small planetesimals captured in the Lagrange point of Jupiter-Sun system during the outer migration of the giant planets, 3.9 billion years ago. This scenario was proposed by A. Morbidelli and colleagues in a series of articles published in May 2005 in ''Nature'' journal.

See also

★ Menoetius (moon)

★ Asteroid moon

Notes

# UC-Berkeley press release on cometary origin

External links

★ Johnston's Archive: detailed orbital and physical data

★ Keck Obs. press release Trojan Asteroid Patroclus: Comet in Disguise?

★ Patroclus and Menoetius web page