617 Patroclus

617 Patroclus (/pəˈtrkləs/ pə-TROH-kləs) is a large binary Jupiter trojan asteroid. It is a dark D-type asteroid and a slow rotator, due to the 103-hour orbital period of its two components. It is one of five Jovian asteroids targeted by the Lucy space probe, and is scheduled for a flyby in 2033.

617 Patroclus
617 Patroclus Hubble.jpg
Hubble Space Telescope image composite of Patroclus and its companion Menoetius, taken in 2018
Discovery [1]
Discovered byA. Kopff
Discovery siteHeidelberg Obs.
Discovery date17 October 1906
Designations
(617) Patroclus
Pronunciation/pəˈtrkləs/[7]
Named after
Πάτροκλος Patroklos
(Greek mythology)[2]
1906 VY · 1941 XC
1962 NB
Jupiter trojan[1][3][4]
Trojan[5][6] · background[6]
AdjectivesPatroclean /pætrəˈklən/[8]
Orbital characteristics[3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc19.15 yr (6,993 d)
Aphelion5.9376 AU
Perihelion4.4959 AU
5.2167 AU
Eccentricity0.1382
11.92 yr (4,352 d)
170.39°
0° 4m 57.72s / day
Inclination22.047°
44.354°
308.15°
Known satellites1 (Menoetius)[9]
Jupiter MOID0.1966 AU
TJupiter2.8360
Physical characteristics
Dimensions127 km × 117 km × 98 km (primary only)[10]
Mean diameter
113±3 km (primary only)[10]
140.36±0.87 km[11]
140.85±3.37 km[12]
140.92±4.7 km[13]
143.14±8.37 km[14]
154 km[10]
Volume1.36×106 km3[10]
Mass(1.36±0.11)×1018 kg[14]
1.20×1018 kg[10]
Mean density
0.88±0.17 g/cm3[14][10]
40 h (at least; dated)[15]
102.8 h[16]
102 h[17]
103.02±0.40 h[18]
103.5±0.3 h[19]
0.047±0.003[11][12][13]
D (Tholen)[20]
C0 (Barucci)[20]
D (Tedesco)[20]
U–B = 0.215±0.045[20]
B–V = 0.710±0.050[21]
V–R = 0.420±0.030[21]
V–I = 0.830±0.020[21]
8.19[3][11][12][13][4]

Patroclus was discovered on 17 October, 1906, by astronomer August Kopff at the Heidelberg Observatory in Germany, and was named after Patroclus in Greek mythology.[1] It was the second trojan to be discovered and the only member of the Trojan camp named after a Greek figure, as the convention of naming one 'camp' after Greek figures of the Trojan War and the other after Trojan figures had not yet been established.[2]

Patroclus was long thought to be one of the largest Jupiter trojans, with a diameter on the order of 150 km. However, in 2001 it was discovered to be a binary asteroid of two similarly sized objects. The name Patroclus is now assigned to the larger component, some 110–115 km in diameter, while the secondary, slightly smaller at 100–105 km in diameter, has been named Menoetius (/mɪˈnʃəs/ mə-NEE-shəs).[a] This was the first discovery of a binary trojan asteroid.[9]

OrbitEdit

Patroclus orbits in Jupiter's trailing Lagrangian point, L5,[9] 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.[3] The asteroid's observation arc begins at the discovering Heidelberg Observatory in November 1906, about 3 weeks after its official discovery observation.[1]

Binary systemEdit

 
Hubble images of Patroclus and Menoetius orbiting each other, from May to June 2017
 
Artist's conception of Patroclus and Menoetius orbiting around their center of mass, occasionally eclipsing one another
 
Artist's impression of the Patroclus-Menoetius binary system
Menoetius
 
Plot of the results of the multi-chord stellar occultation by 617 Patroclus and Menoetius
Discovery
Discovery date2001
Designations
Pronunciation/mɪˈnʃəs/
Named after
Menoetius (Greek mythology)
AdjectivesMenoetian /mɪˈnʃən/[22])
Orbital characteristics
680±20 km[9]
664.6 km[10]
102.8 h
Satellite ofPatroclus
Physical characteristics
Dimensions117 km × 108 km × 90 km[10]
Mean diameter
104±3 km[10]

In 2001, it was discovered that Patroclus is a binary system, made up of two components with of roughly similar size.[9][23][24] It is one of 6 binary Trojan asteroids believed to exist. In 2006, accurate measurements of the orbit from the Keck Laser guide star adaptive optics system were reported.[25]

It was estimated[26] that the two components orbit around their center of mass in 4.283±0.004 days at a distance of 680±20 km in a roughly circular orbit.[9] Combining these observations with thermal measurements taken in 2000, the sizes of the components of the system were estimated at 106 km and 98 km, with an equivalent whole-system diameter of 145 km,[9] refined by later measurements from the Keck Observatory to approximately 122 km and 112 km for each partner,[27] and a co-orbital period of 103.5±0.3 hours (4.3125±0.0125 days).[25][19]

On 21 October 2013, both bodies occulted a magnitude 8.8 star as observed by a team of 41 observers stationed across the USA. Observation data put the orbital distance at the time of 664.6 km (with an unstated uncertainty), and give a size for the slightly larger component, which retains the name Patroclus with overall volume equivalent to a 113±3 km–diameter sphere, with the smaller component now named Menoetius with a volume equivalent to a 104±3 km–diameter sphere.

Physical characteristicsEdit

LightcurvesEdit

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/).[16][17][18][19] 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 albedoEdit

According to the surveys carried out by the Infrared Astronomical Satellite IRAS and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the Patroclus system has an effective combined size between 140.36 and 140.92 kilometers in diameter and its surface has an albedo of 0.047.[11][13] 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.[4]

CompositionEdit

Recent evidence suggests that the objects are icy like comets, rather than rocky like most asteroids. In the Tholen classification, Patroclus is a dark P-type asteroid.[4]

Because the density of the components (0.88 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.[25] 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.[28]

ExplorationEdit

 
Animation of Lucy's trajectory around Sun
  Lucy ·    Sun ·    Earth ·    52246 Donaldjohanson  ·   3548 Eurybates ·    21900 Orus ·    617 Patroclus
 
Artist's impression of the Lucy spacecraft flying past the Patroclus-Menoetius system

The Patroclus–Menoetius system is a scheduled target for Lucy, a flyby mission to multiple asteroids, mostly Jupiter trojans.[29]

NameEdit

This minor planet was named after the legendary Greek hero Patroclus. Friend and lover of Achilles, he was killed by Hector during the Trojan War. (See 588 Achilles and 624 Hektor.) The 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).[2]

In Greek and thus in Latin, Patroclus has all short vowels. Thus the expected English pronunciation would be with stress on the 'a', */ˈpætrəkləs/. However, Alexander Pope shifted the stress to the first 'o', /pəˈtrkləs/,[7] a convention allowed in Latin poetry,[30] for metrical convenience in his verse translation of Homer, and this irregular pronunciation has become established in English.

Patroclus and its moon Menoetius are the only objects in the Trojan camp to be named after Greek rather than Trojan characters. 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).

NotesEdit

  1. ^ Buie (2015). Volume equivalent diameters based on derived ellipsods are: Patroclus: 113 km and Menoetius: 104 km, while for the combined system, a mean-diameter of 154 km is given. Measured by asteroid occultation. Alternative observations gave a combined diameter of 140 kilometers. Summary figures for (617) Patroclus at the LCDB.

ReferencesEdit

  1. ^ a b c d "617 Patroclus (1906 VY)". Minor Planet Center. Retrieved 13 June 2018.
  2. ^ a b c Schmadel, Lutz D. (2007). "(617) Patroclus". Dictionary of Minor Planet Names – (617) Patroclus. Springer Berlin Heidelberg. p. 62. doi:10.1007/978-3-540-29925-7_618. ISBN 978-3-540-00238-3.
  3. ^ a b c d "JPL Small-Body Database Browser: 617 Patroclus (1906 VY)" (2017-06-14 last obs.). Jet Propulsion Laboratory. Retrieved 13 June 2018.
  4. ^ a b c d "LCDB Data for (617) Patroclus". Asteroid Lightcurve Database (LCDB). Retrieved 11 July 2017.
  5. ^ "List of Jupiter Trojans". Minor Planet Center. 20 August 2016. Retrieved 11 July 2017.
  6. ^ a b "Asteroid (617) Patroclus – Proper elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 13 June 2018.
  7. ^ a b "Patroclus". Dictionary.com Unabridged. Random House.
  8. ^ Riggs (1972) The Christian poet in Paradise lost
  9. ^ a b c d e f g Johnston, Wm. Robert (21 September 2014). "(617) Patroclus and Menoetius". johnstonsarchive.net. Retrieved 11 July 2017.
  10. ^ a b c d e f g h i Buie, Marc W.; Olkin, Catherine B.; Merline, William J.; Walsh, Kevin J.; Levison, Harold F.; Timerson, Brad; et al. (March 2015). "Size and Shape from Stellar Occultation Observations of the Double Jupiter Trojan Patroclus and Menoetius". The Astronomical Journal. 149 (3): 11. Bibcode:2015AJ....149..113B. doi:10.1088/0004-6256/149/3/113. Retrieved 11 July 2017.
  11. ^ a b c d Grav, T.; Mainzer, A. K.; Bauer, J. M.; Masiero, J. R.; Nugent, C. R. (November 2012). "WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy". The Astrophysical Journal. 759 (1): 10. arXiv:1209.1549. Bibcode:2012ApJ...759...49G. doi:10.1088/0004-637X/759/1/49. S2CID 119101711. (online catalog)
  12. ^ a b c Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. (online, AcuA catalog p. 153)
  13. ^ a b c d Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 13 June 2018.
  14. ^ a b c Carry, B. (December 2012). "Density of asteroids". Planetary and Space Science. 73 (1): 98–118. arXiv:1203.4336. Bibcode:2012P&SS...73...98C. doi:10.1016/j.pss.2012.03.009. S2CID 119226456. See Table 1.
  15. ^ Gonano, M.; Mottola, S.; Neukum, G.; di Martino, M. (December 1990). "Physical study of outer belt asteroids". Space Dust and Debris; Proceedings of the Topical Meeting of the Interdisciplinary Scientific Commission B /Meetings B2. 11 (12): 197–200. Bibcode:1991AdSpR..11..197G. doi:10.1016/0273-1177(91)90563-Y. ISSN 0273-1177. Retrieved 11 July 2017.
  16. ^ a b Marchis, Franck; Hestroffer, Daniel; Descamps, Pascal; Berthier, Jérô; me; Bouchez, Antonin H.; et al. (February 2006). "A low density of 0.8gcm-3 for the Trojan binary asteroid 617Patroclus". Nature. 439 (7076): 565–567. arXiv:astro-ph/0602033. Bibcode:2006Natur.439..565M. doi:10.1038/nature04350. PMID 16452974. S2CID 4416425. Retrieved 11 July 2017.
  17. ^ a b Behrend, Raoul. "Asteroids and comets rotation curves – (617) Patroclus". Geneva Observatory. Retrieved 11 July 2017.
  18. ^ a b Mueller, Michael; Marchis, Franck; Emery, Joshua P.; Harris, Alan W.; Mottola, Stefano; Hestroffer, Daniel; et al. (February 2010). "Eclipsing binary Trojan asteroid Patroclus: Thermal inertia from Spitzer observations". Icarus. 205 (2): 505–515. arXiv:0908.4198. Bibcode:2010Icar..205..505M. doi:10.1016/j.icarus.2009.07.043. S2CID 118634843.
  19. ^ a b c Oey, Julian (July 2012). "Period Determination of 617 Patroclus". The Minor Planet Bulletin. 39 (3): 106–107. Bibcode:2012MPBu...39..106O. ISSN 1052-8091. Retrieved 11 July 2017.
  20. ^ a b c d "Asteroid 617 Patroclus". Small Bodies Data Ferret. Retrieved 13 June 2018.
  21. ^ a b c Chatelain, Joseph P.; Henry, Todd J.; French, Linda M.; Winters, Jennifer G.; Trilling, David E. (June 2016). "Photometric colors of the brightest members of the Jupiter L5 Trojan cloud". Icarus. 271: 158–169. Bibcode:2016Icar..271..158C. doi:10.1016/j.icarus.2016.01.026. Retrieved 12 June 2018.
  22. ^ Redfield (1994) Nature and culture in the Iliad: the tragedy of Hector
  23. ^ Merline, W. J. (2001), IAUC 7741: 2001fc; S/2001 (617) 1; C/2001 T1, C/2001 T2
  24. ^ "Satellites and Companions of Minor Planets". IAU / CBAT. 17 September 2009. Archived from the original on 21 January 2011. Retrieved 25 January 2011.
  25. ^ a b c 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. (2 February 2006). "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. S2CID 4416425.
  26. ^ Sanders, Robert (2006), Binary asteroid in Jupiter's orbit may be icy comet from solar system's infancy, University of California, Berkeley
  27. ^ Sanders, Robert. "Trojan Binary Asteroid – Patroclus & Menoetius". UC Berkeley. Retrieved 4 October 2017.
  28. ^ Morbidelli, A.; Levison, H. F.; Tsiganis, K.; Gomes, R. (26 May 2005). "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. S2CID 4373366.
  29. ^ Dreier, Casey; Lakdawalla, Emily (30 September 2015). "NASA announces five Discovery proposals selected for further study". The Planetary Society. Retrieved 1 October 2015.
  30. ^ This poetic exception to normal Latin stress assignment is allowed when the final syllable starts with a sequence of two consonants, the first a b c d g p t (a plosive) and the second an l or r (a liquid). It is used for metrical convenience in Latin, and Pope retained it in his English translation.

External linksEdit