617 Patroclus

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

    617 Patroclus (/pəˈtroʊkləs/ 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 (/mᵻˈniːʃəs/ 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

    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

    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 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 provisional designation was S/2001 (617) 1.

    Composition

    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 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]

    Exploration

    Patroclus is a proposed target for Lucy, a mission to several asteroids and 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

    References

    1. ↑ "JPL Small-Body Database Browser: 617 Patroclus (1906 VY)" (last observation: ; arc: years). Jet Propulsion Laboratory. Retrieved 2011-08-30.
    2. 1 2 3 Carry, B. (December 2012), "Density of asteroids", Planetary and Space Science 73, pp. 98–118, arXiv:1203.4336, Bibcode:2012P&SS...73...98C, doi:10.1016/j.pss.2012.03.009. See Table 1.
    3. 1 2 3 4 5 6 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. 1 2 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. arXiv:astro-ph/0602033. Bibcode:2006Natur.439..565M. doi:10.1038/nature04350. PMID 16452974.
    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. doi:10.1038/nature03540. PMID 15917801.
    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

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