624 Hektor

Lore & Background

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 Hector and is thus one of two trojan asteroids that is 'misplaced' in the wrong camp (the other being 617 Patroclus in the Trojan camp).

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. It is thought to be a contact binary, composed of two more rounded lobes of 220 and 183 km mean diameters. Hubble Space Telescope observations in 1993 did not show an obvious bilobate shape due to limited angular resolution, but Keck 10-meter-II-telescope observations on 17 July 2006 indicated a bilobate shape, reinforced by later studies and multiple historical lightcurves suggesting a rotation period of 6.9205 hours.

A 10–15-km-diameter moon, named Skamandrios, was detected orbiting Hektor in 2006 with a semi-major axis of 623.5 km and an orbital period of 2.9651 days. It was confirmed with Keck observations in November 2011 and named on 12 March 2017. Its orbit is highly inclined and eccentric, and its rotation is likely chaotic. Marchis et al. (2014) speculate that it was ejected after a low-velocity collision produced the bilobed primary.

Reader's Guide

624 Hektor holds significance as the largest Jupiter trojan and the namesake of the Hektor family. It is notable for being the first known trojan asteroid with a satellite companion and, as of the article, one of only four known binary trojan asteroids in the L4 group (the others being 16974 Iphthime, 3548 Eurybates, and 15094 Polymele). Its highly elongated shape and contact-binary hypothesis make it a subject of study for understanding asteroid structure and formation. Hektor was included in a 2003 study of asteroids using the Hubble FGS, alongside 63 Ausonia, 15 Eunomia, 43 Ariadne, 44 Nysa, and 624 Hektor. It has 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. The asteroid has also been imaged by the NEOWISE and AKARI all-sky studies, which reported highly divergent size estimates of 147.4 and 231.0 kilometers, respectively, due to large differences in estimated albedo (approximately 0.107 for NEOWISE and 0.034 for AKARI). Hektor is unusually not included in the published IRAS results, making it the largest Jupiter trojan omitted from that study.

Did You Know?

• Hektor is one of two trojan asteroids 'misplaced' in the wrong camp; the other is 617 Patroclus.
• Its moon Skamandrios was discovered in 2006 and confirmed with Keck observations in November 2011.
• The asteroid's density is estimated at 1.0 g/cm³, with a mass of 7.9×10^18 kg.