617 Patroclus

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617 Patroclus
Discovery
Discovered by August Kopff
Discovery date October 17, 1906
Designations
Named after Patroclus
Alternative names 1906 VY; 1941 XC;
1962 NB
Minor planet category Jupiter trojan
Adjective Patroclean
Orbital characteristics[1]
Epoch 2455800.5 (JD 2011-Aug-27.0)
Aphelion 5.9481823 AU
Perihelion 4.4878688 AU
Semi-major axis 5.2180256 AU
Eccentricity 0.1399297
Orbital period 11.9197598 a (4353.6923 d)
Mean anomaly 331.77002°
Inclination 22.05276°
Longitude of ascending node 44.36649°
Argument of perihelion 307.90775°
Physical characteristics
Dimensions 143.14 ± 8.37[2] km
Mass (1.36 ± 0.11) × 1018[2] kg
Mean density 0.88 ± 0.17[2] g/cm3
Rotation period >4.283±0.004 days
Albedo 0.047
Temperature 110 K
Spectral type P-type
Absolute magnitude (H) 8.19

617 Patroclus (/pəˈtrkləs/ 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.[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 (/mɨˈnʃəs/ 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.

Orbit[edit]

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 object, 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, describing 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 122 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 provisional designation was S/2001 (617) 1.

Composition[edit]

Because of 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 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]

See also[edit]

References[edit]

  1. ^ JPL Small-Body Database Browser Retrieved 2011-08-30
  2. ^ a b c 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.
  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. 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. doi:10.1038/nature04350. PMID 16452974.  edit
  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. doi:10.1038/nature03540. PMID 15917801.  edit

External links[edit]