617 Patroclus
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| Discovery A | |
|---|---|
| Discoverer | August Kopff |
| Discovery date | October 17, 1906 |
| Alternate designations B |
1906 VY; 1941 XC; 1962 NB |
| Category | Jupiter Trojan |
| Orbital elements C | |
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|
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| Eccentricity (e) | 0.138 |
| Semi-major axis (a) | 5.228 AU |
| Perihelion (q) | 4.506 AU |
| Aphelion (Q) | 5.950 AU |
| Orbital period (P) | 4365.7 d (11.95 a) |
| Mean orbital speed | ??? |
| Inclination (i) | 22.03° |
| Longitude of the ascending node (Ω) |
44.37° |
| Argument of perihelion (ω) |
307.81° |
| Mean anomaly (M) | 149.94° |
| Physical characteristics D | |
| Dimensions | 122 km and 112 km |
| Mass | 1.36×1018 kg |
| Density | 0.8 g/cm³ |
| Surface gravity | ??? |
| Escape velocity | ??? |
| Rotation period | >4.283±0.004 days |
| Spectral class | P-type |
| Absolute magnitude | 8.19 |
| Albedo (geometric) | 0.047 |
| Mean surface temperature |
110 K |
617 Patroclus (pə-troe'-kləs, IPA: /pəˈtroʊkləs/) is a binary minor planet made up of two similarly-sized objects orbiting their common centre of gravity. It is classified as a Trojan asteroid, sharing an orbit with Jupiter. It was discovered in 1906 by August Kopff, and was the second Trojan to be discovered.[1] Its binary nature was discovered in 2001; the name Patroclus now refers to the larger of the two components, while its slightly smaller companion body has been named Menoetius (IPA: /mɨˈniːtiəs/, IPA: /mɨˈniːʃəs/, official designation (617) Patroclus I Menoetius). Recent evidence suggests that the objects are icy comets, rather than rocky asteroids.
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[edit] Orbit
Patroclus orbits in Jupiter's trailing Lagrangian point, L5,[1] in an orbit called the 'Trojan node' after one of the sides in the legendary Trojan War (the other node 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 Trojan asteroids were not adopted until after Patroclus was named (similarly, the asteroid Hektor is the only Trojan character to appear in the Greek camp).
[edit] Binary system
In 2001, it was discovered that Patroclus is a binary object, made up of two components of roughly similar size.[2][1] 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[3] 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.[1] 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.[1] The smaller component, measuring 112 km, is now named Menoetius[1], after the legendary Patroclus's father. Its provisional designation was S/2001 (617) 1.
[edit] Composition
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 Trojan asteroids are in fact small planetesimals captured in the Lagrange point of Jupiter-Sun system during the outer 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.
[edit] See also
[edit] Notes
- ^ a b c d e f Johnston, Wm. Robert (2006), (617) Patroclus and Menoetius, <http://www.johnstonsarchive.net/astro/astmoons/am-00617.html>
- ^ Merline, W. J. (2001), IAUC 7741: 2001fc; S/2001 (617) 1; C/2001 T1, C/2001 T2, <http://cfa-www.harvard.edu/iauc/07700/07741.html>
- ^ Sanders, Robert (2006), Binary asteroid in Jupiter's orbit may be icy comet from solar system's infancy, University of California, Berkeley, <http://www.berkeley.edu/news/media/releases/2006/02/01_patroclus.shtml>
[edit] External links
- Keck Obs. press release Trojan Asteroid Patroclus: Comet in Disguise?
- Patroclus and Menoetius web page
- Orbital simulation from JPL (Java) / Ephemeris
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