|Discovered by||A. Kopff|
|Discovery site||Heidelberg Obs.|
|Discovery date||17 October 1906|
|MPC designation||(617) Patroclus|
|1906 VY · 1941 XC
|Jupiter trojan 
|Orbital characteristics |
|Epoch 16 February 2017 (JD 2457800.5)|
|Uncertainty parameter 0|
|Observation arc||19.15 yr (6,993 days)|
|11.92 yr (4,353 days)|
|0° 4m 57.72s / day|
|Known satellites||1 |
|Jupiter MOID||0.1992 AU|
|Jupiter Tisserand parameter||2.8360|
|Dimensions||±0.87 km 140.36
±0.868 km 140.362
±3.37 km 140.85
±4.7 km ( 140.92IRAS:8)
±8.37 km (avg.) 143.14
|Mass||±0.11)×1018 kg (1.36|
|±0.17 g/cm3 0.88|
|>40 h (dated)
±0.40 h 103.02
±0.3 h 103.5
±0.003 (IRAS:8) 0.0471
|Tholen = P  · P 
B–V = 0.677
U–B = 0.215
617 Patroclus (// pə-TROH-kləs), provisional designation 1906 VY is a dark Jupiter trojan, slow rotator and binary system from the Trojan camp, approximately 140 kilometers in diameter. It was discovered on 17 October 1906, by German astronomer August Kopff at Heidelberg Observatory in southwest Germany. In 2001, its minor-planet moon, named Menoetius (// mi-NEE-shəs; official designation (617) Patroclus I Menoetius) was discovered. The satellite is slightly smaller than its primary.
The asteroid was named after Patroclus from Greek mythology. It was the second trojan to be discovered and the only member of the Trojan camp named after a Greek character. It was also the first known binary system among the Trojans. Patroclus is one of five Jupiter trojans target by the Lucy space probe.
Patroclus orbits in Jupiter's trailing Lagrangian point, L5, in an area called the Trojan camp after one of the sides in the legendary Trojan War (the other node, at the L4 point, is called the "Greek camp").
It orbits the Sun at a distance of 4.5–5.9 AU once every 11 years and 11 months (4,353 days). Its orbit has an eccentricity of 0.14 and an inclination of 22° with respect to the ecliptic. The asteroid's observation arc begins at the discovering Heidelberg Observatory in November 1906, about 3 weeks after its official discovery observation.
In 2001, it was discovered that Patroclus is a binary system, made up of two components with a minor-planet moon of roughly similar size. It is one of 18 binary Trojan asteroids known to exist. In 2006, accurate measurements of the orbit from the Keck Laser guide star adaptive optics system were reported.
It was estimated that the two components orbit around their center of mass in 4.283±0.004 d at a distance of 680±20 km in a roughly circular orbit. Combining these observations with thermal measurements taken in 2000, the sizes of the components of the system were estimated. The slightly larger component, which measures 141 km in diameter, retains the name Patroclus. The smaller component, measuring 112 km, is now named Menoetius, after the legendary Patroclus's father. It was previously known by the provisional designation S/2001 (617) 1.
Because the density of the components (0.8 g/cm³) is less than water and about one third that of rock, it was suggested 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 the 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.
Since 1989, several rotational lightcurves of Patroclus have been obtained from photometric observations. Analysis of the best rated lightcurves gave a rotation period between 102.8 and 103.5 hours with a brightness amplitude of less than 0.1 magnitude (U=2/3/). A low brightness variation typically indicates that a body has a nearly spheroidal shape. Its long rotation period makes it a slow rotator.
Diameter and albedo
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Patroclus measures between 140.36 and 140.92 kilometers in diameter and its surface has an albedo of 0.047. The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0471 and a diameter of 140.92 kilometers based on an absolute magnitude of 8.19.
|Source: JPL Small-Body Database, IRAS data|
- 52246 Donaldjohanson — 20 April 2025: 4 km diameter C-type asteroid in the inner main-belt, member of ~130Myr old Erigone family;
- 3548 Eurybates — 12 August 2027: 64 km diameter C-type Jupiter Trojan in the Greek camp at L4, largest member of the only confirmed disruptive collisional family in the Trojans;
- 15094 Polymele — 15 September 2027: 21 km diameter P-type Trojan at L4, likely collisional fragment;
- 11351 Leucus — 18 April 2028: 34 km diameter D-type slow rotator Trojan at L4;
- 21900 Orus — 11 November 2028: 51 km diameter D-type Trojan at L4;
- 617 Patroclus — 2 March 2033: P-type binary Trojan. The primary, Patroclus, has a mean diameter of 113 km and its companion, Menoetius, has a diameter of 104 km. The pair orbit at a separation of 680 km. The binary resides in the Trojan camp at L5.
This minor planet was named after the Greek hero Patroclus from Greek mythology. Friend of Achilles, he was killed by Hector during the Trojan War (see also (588) and (624)). The minor planet's name was proposed by Austrian astronomer Johann Palisa. The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 65).
Patroclus is the only object in the Trojan camp to be named after a Greek rather than a Trojan 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).
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- 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. Archived from the original on 2011-01-21. Retrieved 2011-01-25.
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- Sanders, Robert (2006), Binary asteroid in Jupiter's orbit may be icy comet from solar system's infancy, University of California, Berkeley
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- Keck Obs. press release Trojan Asteroid Patroclus: Comet in Disguise?
- Patroclus and Menoetius web page
- Asteroids with Satellites, Robert Johnston, johnstonsarchive.net
- Asteroid Lightcurve Database (LCDB), query form (info)
- Dictionary of Minor Planet Names, Google books
- Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend
- Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
- 617 Patroclus at the JPL Small-Body Database