617 Patroclus

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617 Patroclus
Discovered by August Kopff
Discovery date 17 October 1906
MPC designation (617) Patroclus
Named after
1906 VY; 1941 XC;
1962 NB
Jupiter trojan
Adjectives Patroclean
Orbital characteristics[1]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc 109.49 yr (39991 d)
Aphelion 5.9400011 AU (888.61152 Gm)
Perihelion 4.4947726 AU (672.40841 Gm)
5.2173868 AU (780.50996 Gm)
Eccentricity 0.1385012
11.92 yr (4352.89 d)
0° 4m 57.733s / day
Inclination 22.047388°
Earth MOID 3.54052 AU (529.654 Gm)
Jupiter MOID 0.199741 AU (29.8808 Gm)
Jupiter Tisserand parameter 2.836
Physical characteristics
Mean radius
70.46±2.35 km[1]
71.57 ± 4.185 km[2]
Mass (1.36 ± 0.11) × 1018 kg [2]
Mean density
0.88 ± 0.17 g/cm3[2]
102.8 h (4.28 d)
Temperature 110 K

617 Patroclus (/pəˈtrkləs/ pə-TROH-kləs) is a binary minor planet made up of two objects of similar size orbiting their barycenter. It is a Jupiter trojan. It was discovered in 1906 by August Kopff, and was the second trojan to be discovered.[3] 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 (/mˈnʃəs/ 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,[3] 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).

Binary system[edit]

In 2001, it was discovered that Patroclus is a binary system, made up of two components of roughly similar size.[3][4][5] In 2006, accurate measurements of the orbit from the Keck Laser guide star adaptive optics system were reported.[6] It was estimated[7] 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.[3] 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.[3] The smaller component, measuring 112 km, is now named Menoetius,[3] after the legendary Patroclus's father. Its has 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.[6] 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.[8]


Patroclus is a proposed target for Lucy, a mission to several asteroids, mostly Jupiter trojans.[9]

The largest Jupiter trojans
Trojan Diameter (km)
624 Hektor 225
911 Agamemnon 167
1437 Diomedes 164
1172 Äneas 143
617 Patroclus 141
588 Achilles 135
1173 Anchises 126
1143 Odysseus 126
Source: JPL Small-Body Database, IRAS data

See also[edit]


  1. ^ a b "JPL Small-Body Database Browser: 617 Patroclus (1906 VY)" (last observation: ; arc: years). Jet Propulsion Laboratory. Retrieved 7 May 2016. 
  2. ^ a b c Carry, B. (December 2012), "Density of asteroids", Planetary and Space Science, 73, pp. 98–118, Bibcode:2012P&SS...73...98C, arXiv:1203.4336Freely accessible, doi:10.1016/j.pss.2012.03.009.  See Table 1.
  3. ^ a b c d e f Johnston, Wm. Robert (2006), (617) Patroclus and Menoetius 
  4. ^ Merline, W. J. (2001), IAUC 7741: 2001fc; S/2001 (617) 1; C/2001 T1, C/2001 T2 
  5. ^ "Satellites and Companions of Minor Planets". IAU / CBAT. 2009-09-17. Archived from the original on 2011-01-21. Retrieved 2011-01-25. 
  6. ^ a b Marchis, F.; Hestroffer, D.; Descamps, P.; Berthier, J. R. M.; Bouchez, A. H.; Campbell, R. D.; Chin, J. C. Y.; Van Dam, M. A.; Hartman, S. K.; Johansson, E. M.; Lafon, R. E.; Le Mignant, D. L.; De Pater, I.; Stomski, P. J.; Summers, D. M.; Vachier, F. D. R.; Wizinovich, P. L.; Wong, M. H. (2006-02-02). "A low density of 0.8 g cm-3 for the Trojan binary asteroid 617 Patroclus". Nature. 439 (7076): 565–567. Bibcode:2006Natur.439..565M. PMID 16452974. arXiv:astro-ph/0602033Freely accessible. doi:10.1038/nature04350. 
  7. ^ Sanders, Robert (2006), Binary asteroid in Jupiter's orbit may be icy comet from solar system's infancy, University of California, Berkeley 
  8. ^ Morbidelli, A.; Levison, H. F.; Tsiganis, K.; Gomes, R. (2005-05-26). "Chaotic capture of Jupiter's Trojan asteroids in the early Solar System". Nature. 435 (7041): 462–465. Bibcode:2005Natur.435..462M. PMID 15917801. doi:10.1038/nature03540. 
  9. ^ Dreier, Casey; Lakdawalla, Emily (30 September 2015). "NASA announces five Discovery proposals selected for further study". The Planetary Society. Retrieved 2015-10-01. 

External links[edit]