SETI Releases Paper About Hektor, a Dual Shape Trojan Asteroid With a Small Moon

Posted on March 1, 2014

This dual shape Trojan asteroid, named (624) Hektor, has a small moon orbiting it. Hektor is the only known Trojan asteroid to possess a small satellite. The unusual system has been studied by scientists from the SETI Institute for the past eight years.

SETI calls the unique system a "complex mini geological world" in a release. The moon was detected in 2006. The study found the 12 kilometer moon orbits the 250 km asteroid every 3 days at a distance of 600 km in an ellipse inclined almost 45 degrees with respect to the asteroid's equator. The researchers also found the asteroid is made of a mixture of rock and ices.

The new study also suggests the asteroid and its moons are the result of the collision of two asteroids. SETI researchers used W. M. Keck Observatory data and photometric observations to come up with the conclusion. They also collaborated with researchers from the University of California at Berkeley. The researchers had to overcome some technical and mathematical hurdles before they could release the paper.

Franck Marchis, astronomer at the Carl Sagan center of the SETI Institute, says in a release, "The major one was technical: the satellite can be seen only with a telescope like Keck Observatory's fitted with LSG-AO, but time on the mighty Keck's is highly prized and in limited availability. Secondly, the orbit of the satellite is so bizarre that we had to develop a complex new algorithm to be able to pin it down and understand its stability over time."

Matija Cuk, coauthor and scientist at the Carl Sagan Center of the SETI Institute, says, "The orbit of the moon is elliptical and tilted relative to the spin of Hektor, which is very different from other asteroids with satellites seen in the main-belt. However, we did computer simulations, which include Hektor being a spinning football shape asteroid and orbiting the Sun, and we found that the moon's orbit is stable over billions of years."

The research paper, "The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor," is published here in the Astrophysical Journal Letters.



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