624 Hektor

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624 Hektor
Star field showing Hektor (apmag 15)
Discovered by A. Kopff
Discovery site Heidelberg Obs.
Discovery date 10 February 1907
MPC designation (624) Hektor
Pronunciation /ˈhɛktɔːr/ HEK-tor
Named after
Hector (Greek mythology)
1907 XM; 1948 VD
Jupiter trojan[1] · Hektor[2]
(Greek camp)[3]
Adjectives Hektorian
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc 110.08 yr (40,205 days)
Aphelion 5.3824 AU
Perihelion 5.1297 AU
5.2561 AU
Eccentricity 0.0240
12.05 yr (4,401 days)
0° 4m 54.48s / day
Inclination 18.167°
Known satellites 1 (Skamandrios; D: 12±3 km[4]
Jupiter MOID 0.276 AU
TJupiter 2.8990
Physical characteristics
Dimensions 370 × 195 × 195 km[5]
403 × 201 km (derived)[4]
Mean diameter
147.37±2.33 km[6]
225 km[1]
226.68±15.15 km[7]
230.99±3.94 km[8]
250±26 km (equivalent diameter)[4]
Mass (9.95±0.12)×1018 kg[7]
(7.9±1.4)×1018 kg[4]
Mean density
1.0±0.3 g/cm3[4]
1.63±0.32 g/cm3[7]
2.43±0.35 g/cm3[9]
6.9205 hours (0.28835 d)[4]
D (Tholen)[1]
13.79 to 15.26[citation needed]
7.20[6] · 7.3[1] · 7.49[8]
0.078" to 0.048"[citation needed]

624 Hektor (/ˈhɛktɔːr/ HEK-tor) is the largest Jupiter trojan and the namesake of the Hektor family, with a highly elongated shape equivalent in volume to a sphere of approximately 225 to 250 kilometers diameter. It was discovered on 10 February 1907, by astronomer August Kopff at Heidelberg Observatory in southwest Germany, and named after Hektor from Greek mythology. It has one small (~12km) satellite, Skamandrios, discovered in 2006.


Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, L4, called the 'Greek' node after one of the two sides in the legendary Trojan War. Hektor is named after the Trojan hero Hektor and is thus one of two trojan asteroids that is "misplaced" in the wrong camp (the other one being 617 Patroclus in the Trojan node).

Contact binary plus moon[edit]

Hektor is one of the most elongated bodies of its size in the Solar System, being approximately 403 km in its longest dimension, but averaging only around 201 km in its other dimensions, with a total volume equivalent to an approx 250 km diameter sphere, and an estimated mass of 7.9×1018 kg (thus density of 1.0g/cm3). It is thought that Hektor might be a contact binary (two asteroids joined by gravitational attraction) like 216 Kleopatra, composed of two more rounded lobes of 220 and 183 km mean diameters[4]. Hubble Space Telescope observations of Hektor in 1993 did not show an obvious bilobate shape because of a limited angular resolution. On 17 July 2006, the Keck 10-meter-II-telescope and its laser guide star adaptive optics (AO) system indicated a bilobate shape for Hektor[10], which was reinforced by later studies that, together with multiple historical lightcurves, suggest a rotation period of 6.9205 hours.[4]

Additionally, a 12-km-diameter moon of Hektor, named Skamandrios, S/2006 (624) 1, was detected orbiting with a semi-major axis of 623.5 km and an orbital period of 2.9651 days (71.162 hours).[11][4] It was confirmed with Keck observations in November 2011.[12] No mass estimate was provided, but the equivalent volume suggests an approximate mass of 8.74×1014 kg if the two bodies are of the same density.

Hektor is, so far, the only known binary trojan asteroid in the L4 point and the first known trojan with a satellite companion. 617 Patroclus, another large trojan asteroid located in the L5, is composed of two almost equal-sized components.[10]

The largest Jupiter trojans
Trojan Diameter (km)
624 Hektor 225
617 Patroclus 140
911 Agamemnon 131
588 Achilles 130
3451 Mentor 126
3317 Paris 119
1867 Deiphobus 118
1172 Äneas 118
1437 Diomedes 118
1143 Odysseus 115
Source: JPL Small-Body Database, NEOWISE data


624 Hektor was in a 2003 study of asteroids using the Hubble FGS.[13] Asteroids studied include (63) Ausonia, (15) Eunomia, (43) Ariadne, (44) Nysa, and (624) Hektor.[14]. It has since been revisited several times, particularly as a test of the upgraded resolution of the Keck Observatory's LGS Adaptive Optics system which allowed Earth-based observation of binary asteroids for the first time,[10][4] the asteroid has also been imaged by the NEOWISE and AKARI all-sky studies, which reported highly divergent size estimates of 147.4[6] and 231.0 kilometers [8] respectively, although this mostly arises from large differences in estimated albedo (approximately 0.107 for NEOWISE, and a much lower 0.034 for AKARI) rather than its absolute magnitude being measured only briefly at opposing extremes of a widely varying cycle such as thought to account for the uncertainty over the size of 1173 Anchises (624 Hektor's own abs. mag. recorded as a relatively similar 7.20 and 7.49 by the two studies). It is, unusually, not included in the published IRAS results, and is therefore the largest Jupiter trojan to be omitted from that study.

Hektor in fiction[edit]


  1. ^ a b c d e f "JPL Small-Body Database Browser: 624 Hektor (1907 XM)" (5 September 2008 last obs). Retrieved 1 November 2008. 
  2. ^ "Small Bodies Data Ferret". Nesvorny HCM Asteroid Families V3.0. Retrieved 19 October 2017. 
  3. ^ "List of Jupiter Trojans". Minor Planet Center. 4 October 2017. Retrieved 19 October 2017. 
  4. ^ a b c d e f g h i j Marchis, Frank; Durech, Josef; Castillo-Rogez, Julie; Vachier, Frédéric; Ćuk, Matija; Berthier, Jérôme; Wong, Michael H.; Kalas, Paul; Duchene, Gaspard; van Dam, Marcos A.; Hamanowa, H.; Viikinkoski, M. (28 February 2014). "The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor". The Astrophysical Journal Letters. L37 (2014). arXiv:1402.7336Freely accessible. Bibcode:2014ApJ...783L..37M. doi:10.1088/2041-8205/783/2/L37. 
  5. ^ Storrs, Alex; Weiss, B.; Zellner, B. (1998). "Imaging Observations of Asteroids with Hubble Space Telescope" (PDF). Icarus. 137 (2): 260–268. Bibcode:1999Icar..137..260S. doi:10.1006/icar.1999.6047. Archived from the original (PDF) on 30 October 2008. Retrieved 22 May 2008. 
  6. ^ a b c d "WISE/NEOWISE Observations of the Jovian Trojan Population (Online Data Query) (NB. pad asteroid # to 5 digits with leading 0s)". Retrieved 18 August 2016. 
  7. ^ a b c Carry, B. (December 2012), "Density of asteroids", Planetary and Space Science, 73, pp. 98–118, arXiv:1203.4336Freely accessible, Bibcode:2012P&SS...73...98C, doi:10.1016/j.pss.2012.03.009.  See Table 1.
  8. ^ a b c d "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey (Online Data Query)". October 2011. Retrieved 18 August 2016. 
  9. ^ Descamps, Pascal (2015). "Dumb-bell-shaped equilibrium figures for fiducial contact-binary asteroids and EKBOs". Icarus. 245: 64–79. arXiv:1410.7962Freely accessible. Bibcode:2015Icar..245...64D. doi:10.1016/j.icarus.2014.08.002. ISSN 0019-1035. 
  10. ^ a b c Franck Marchis. "Searching and Characterizing Multiple Trojan Asteroids with LGS AO Systems" (PDF). 
  11. ^ "IAUC 8732: S/2006 (624) 1 (Satellite Discovery)". Retrieved 23 July 2006. 
  12. ^ @AllPlanets (11 November 2011). "Dome closed, Keck telescope is..." (Tweet) – via Twitter. 
  13. ^ Tanga, P.; Hestroffer, D.; Cellino, A.; Lattanzi, M.; Martino, M. Di; Zappalà, V. (2003-04-01). "Asteroid observations with the Hubble Space Telescope FGS". Astronomy & Astrophysics. 401 (2): 733–741. Bibcode:2003A&A...401..733T. doi:10.1051/0004-6361:20030032. ISSN 0004-6361. 
  14. ^ Tanga, P.; Hestroffer, D.; Cellino, A.; Lattanzi, M.; Martino, M. Di; Zappalà, V. (2003-04-01). "Asteroid observations with the Hubble Space Telescope FGS". Astronomy & Astrophysics. 401 (2): 733–741. Bibcode:2003A&A...401..733T. doi:10.1051/0004-6361:20030032. ISSN 0004-6361. 

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