624 Hektor

624 Hektor /ˈhɛktər/ 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 the Trojan prince Hector, from Greek mythology.[1][3] It has one small 12-kilometer sized satellite, Skamandrios, discovered in 2006.[7]

624 Hektor
624 Hektor and its moon Skamandrios
Discovery [1]
Discovered byA. Kopff
Discovery siteHeidelberg Obs.
Discovery date10 February 1907
Designations
(624) Hektor
Pronunciation/ˈhɛktər/[2]
Named after
Hector (Greek mythology)[3]
1907 XM; 1948 VD
Jupiter trojan [1][4] · Hektor [5]
Greeks Greeks[6]
AdjectivesHektorean or Hektorian
(both /hɛkˈtɔːriən/)[2]
Orbital characteristics [4]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc111.28 yr (40,646 d)
Aphelion5.3824 AU
Perihelion5.1319 AU
5.2571 AU
Eccentricity0.0238
12.05 yr (4,403 d)
136.09°
0° 4m 54.48s / day
Inclination18.166°
342.79°
185.22°
Known satellites1
Jupiter MOID0.2752 AU
TJupiter2.8990
Physical characteristics
Dimensions403 km × 201 km (derived)[7]
370 km × 195 km × 195 km[8]
Mean diameter
250±26 km[7]
(if bilobe: 256±12 km)[7]
225 km[4]
147±2 km[9]
227±15 km[10]
231±4 km[11]
Mass(7.9±1.4)×1018 kg[7]
(9.95±0.12)×1018 kg[10]
Mean density
1.0±0.3 g/cm3[7]
1.63±0.32 g/cm3[10]
2.43±0.35 g/cm3[12]
6.9205 hours (0.28835 d)[7]
0.025[4]
0.034±0.001[11]
0.107±0.011[9]
D (Tholen)[4]
13.79 to 15.26
7.20[9] · 7.3[4] · 7.49[11]
0.078" to 0.048"

    Description

    Hektor is a D-type asteroid, dark and reddish in colour. It lies in Jupiter's leading Lagrangian point, L4, called the Greek camp 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 camp).

    Contact-binary hypothesis
    Modelled shape of 624 Hektor from its light curve. Note that Skamandrios is not part of this model.

    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.[7] 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,[13] which was reinforced by later studies that, together with multiple historical lightcurves, suggest a rotation period of 6.9205 hours.[7]

    Satellite
    "Skamandrios (moon)" redirects here. For the mythological figure, see Scamandrius.
    Skamandrios
    Discovery[7]
    Discovered byMarchis et al.
    Discovery date2006 July 16
    Designations
    Designation
    		Hektor I
    Pronunciation/skəˈmændriəs/
    Named after
    		Scamandrius
    S/2006 (624) 1
    AdjectivesSkamandrian
    Orbital characteristics[7]
    623.5±10 km
    Eccentricity0.31±0.03
    2.9651±0.0003 days
    Inclination50.1°±1.1° (to primary)
    166.2°±3.2° (in EQJ2000)
    170.7°±6.1° (in EQJ2000)
    113.4°±1.4° (in EQJ2000)
    Physical characteristics
    Mean diameter
    		12±3 km (assuming composition of primary)

      A 10–15-km-diameter moon, named Skamandrios, was detected orbiting 624 Hektor in 2006 with a semi-major axis of 623.5 km and an orbital period of 2.9651 days (71.162 hours).[14][7] It was confirmed with Keck observations in November 2011,[15] and was then named on 12 March 2017.[16] 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. Its orbit is highly inclined and eccentric, and it is likely that its rotation is chaotic. Marchis et al. (2014) speculate that it was ejected after a low-velocity collision produced the bilobed primary. The newly merged primary could have spun fast enough to be unstable and shed some mass.[7] The dynamics of Skamandrios can be modeled by the restricted four-body problem.[17]

      Hektor is the first known trojan with a satellite companion and, so far, one of only four known binary trojan asteroids in the L4 group (the others being 16974 Iphthime, 3548 Eurybates, and 15094 Polymele). 617 Patroclus, another large trojan asteroid of the L5 group, consists of two almost equal-sized components.[13] Two other binary asteroids are known in the L5 group, (17365) 1978 VF11 and 29314 Eurydamas.[18]

      Studies

      624 Hektor was in a 2003 study of asteroids using the Hubble FGS.[19] Asteroids studied include 63 Ausonia, 15 Eunomia, 43 Ariadne, 44 Nysa, and 624 Hektor.[19] 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.[13][7] The asteroid has also been imaged by the NEOWISE and AKARI all-sky studies, which reported highly divergent size estimates of 147.4[9] and 231.0 kilometers,[11] respectively. 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.

      References
      1. "624 Hektor (1907 XM)". Minor Planet Center. Retrieved 14 June 2018.
      2. "Hector". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
      3. Schmadel, Lutz D. (2007). "(624) Hektor". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 63. doi:10.1007/978-3-540-29925-7_625. ISBN 978-3-540-00238-3.
      4. "JPL Small-Body Database Browser: 624 Hektor (1907 XM)" (2018-05-25 last obs.). Jet Propulsion Laboratory. Retrieved 14 June 2018.
      5. "Asteroid 624 Hektor – Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret. Retrieved 24 October 2019.
      6. "List of Jupiter Trojans". Minor Planet Center. 4 October 2017. Retrieved 19 October 2017.
      7. Marchis, F.; Durech, J.; Castillo-Rogez, J.; Vachier, F.; Cuk, M.; Berthier, J.; et al. (March 2014). "The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor". The Astrophysical Journal Letters. 783 (2): 6. arXiv:1402.7336. Bibcode:2014ApJ...783L..37M. doi:10.1088/2041-8205/783/2/L37. S2CID 19868908.
      8. Storrs, Alex; Weiss, Ben; Zellner, Ben; Burleson, Win; Sichitiu, Rukmini; Wells, Eddie; et al. (February 1999). "Imaging Observations of Asteroids with Hubble Space Telescope". Icarus. 137 (2): 260–268. Bibcode:1999Icar..137..260S. doi:10.1006/icar.1999.6047. S2CID 274199.
      9. 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)
      10. 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.
      11. 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)
      12. Descamps, Pascal (January 2015). "Dumb-bell-shaped equilibrium figures for fiducial contact-binary asteroids and EKBOs". Icarus. 245: 64–79. arXiv:1410.7962. Bibcode:2015Icar..245...64D. doi:10.1016/j.icarus.2014.08.002. S2CID 119272485.
      13. Franck Marchis (November 2005). "Searching and Characterizing Multiple Trojan Asteroids with LGS AO Systems" (PDF) (PDF). Archived from the original (PDF) on 28 July 2020. Retrieved 14 June 2018.
      14. "IAUC 8732: S/2006 (624) 1 (Satellite Discovery)". Central Bureau for Astronomical Telegrams. International Astronomical Union. 21 July 2006. Retrieved 14 June 2018.
      15. @AllPlanets (11 November 2011). "Dome closed, Keck telescope is..." (Tweet) – via Twitter.
      16. "M.P.C. 103967" (PDF). Minor Planet Circular. Minor Planet Center. 12 March 2017. Retrieved 15 October 2020.
      17. Burgos-García, Jaime; Celletti, Alessandra; Gales, Catalin; Gidea, Marian; Lam, Wai-Ting (16 July 2020). "Hill Four-Body Problem with Oblate Bodies: An Application to the Sun–Jupiter–Hektor–Skamandrios System". Journal of Nonlinear Science. Springer Science and Business Media LLC. 30 (6): 2925–2970. Bibcode:2020JNS....30.2925B. doi:10.1007/s00332-020-09640-x. ISSN 0938-8974. S2CID 225526961.
      18. "Johnson's Archive - asteroids with satellites". Retrieved 25 October 2020.
      19. Tanga, P.; Hestroffer, D.; Cellino, A.; Lattanzi, M.; Di Martino, M.; Zappalà, V. (April 2003). "Asteroid observations with the Hubble Space Telescope. II. Duplicity search and size measurements for 6 asteroids" (PDF). Astronomy and Astrophysics. 401 (2): 733–741. Bibcode:2003A&A...401..733T. doi:10.1051/0004-6361:20030032. Retrieved 14 June 2018.

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