|Discovered by||August Kopff|
|Discovery date||October 17, 1906|
|Alternative names||1906 VY; 1941 XC;
|Minor planet category||Jupiter trojan|
|Epoch 2455800.5 (JD 2011-Aug-27.0)|
|Semi-major axis||5.2180256 AU|
|Orbital period||11.9197598 a (4353.6923 d)|
|Longitude of ascending node||44.36649°|
|Argument of perihelion||307.90775°|
|Dimensions||143.14 ± 8.37 km|
|Mass||(1.36 ± 0.11) × 1018 kg|
|Mean density||0.88 ± 0.17 g/cm3|
|Rotation period||>4.283±0.004 days|
|Absolute magnitude (H)||8.19|
617 Patroclus (// pə-TROH-kləs) is a binary minor planet made up of two objects of similar size orbiting their common centre of gravity. It is a Jupiter trojan. It was discovered in 1906 by August Kopff, and was the second trojan to be discovered. Its binary nature was discovered in 2001; the name Patroclus now refers to the larger of the two components, whereas its slightly smaller companion body has been named Menoetius (// mə-NEE-shəs, official designation (617) Patroclus I Menoetius). Recent evidence suggests that the objects are icy like comets, rather than rocky like most asteroids.
Patroclus orbits in Jupiter's trailing Lagrangian point, L5, in an area called the 'Trojan node' after one of the sides in the legendary Trojan War (the other node, at the L4 point, 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 Jupiter trojans were not adopted until after Patroclus was named (similarly, the asteroid Hektor is the only Trojan character to appear in the Greek camp).
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, after the legendary Patroclus's father. Its provisional designation was S/2001 (617) 1.
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 Jupiter trojans are in fact small planetesimals captured in the Lagrange point of Jupiter–Sun system during the 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.
- JPL Small-Body Database Browser Retrieved 2011-08-30
- Carry, B. (December 2012), "Density of asteroids", Planetary and Space Science 73: 98–118, arXiv:1203.4336, Bibcode:2012P&SS...73...98C, doi:10.1016/j.pss.2012.03.009. See Table 1.
- Johnston, Wm. Robert (2006), (617) Patroclus and Menoetius
- Merline, W. J. (2001), IAUC 7741: 2001fc; S/2001 (617) 1; C/2001 T1, C/2001 T2
- "Satellites and Companions of Minor Planets". IAU / CBAT. 2009-09-17. Retrieved 2011-01-25.
- Sanders, Robert (2006), Binary asteroid in Jupiter's orbit may be icy comet from solar system's infancy, University of California, Berkeley
- Keck Obs. press release Trojan Asteroid Patroclus: Comet in Disguise?
- Patroclus and Menoetius web page
- Orbital simulation from JPL (Java) / Ephemeris