View Full Version : Bizarre Orbit of Weird Asteroid's Moon Revealed

28th February 2014, 16:26
Artist impression of the Trojan system showing Hektor and its moon.

If you had to imagine the weirdest-looking space rock, you might imagine the form of asteroid 624 Hektor, the largest known Trojan asteroid in the solar system. Its bi-lobed shape makes it look like a really big cartoon dog bone, or even a huge peanut. What’s more, despite its knobbly appearance (and just as knobbly gravitational field), it even has its own moon. Now astronomers have taken a long, hard look at this exotic rocky beast and pinned down the bizarre orbit 624 Hektor’s moon, finding that the orbit will remain remarkably stable for billions of years.

The 250 kilometer (155 mile) wide 624 Hektor was discovered in 1907 by German astronomer August Kopff, but the existence of its 12 kilometer (7.5 mile) moon wasn’t revealed until 2006 by a team led by SETI Institute astronomer Franck Marchis. Now, eight years of observations of the motion of 624 Hektor’s natural satellite have finally hit paydirt.

Trojans are a special sub-class of asteroid. Trapped in an orbital resonance with Jupiter, they orbit the sun with the same period occupying two regions 60 degrees ahead and 60 degrees behind the gas giant. 624 Hektor is the only Trojan known to possess its own moon.

The technical hurdles are many when trying to observe Trojan asteroids — they are distant and very faint, requiring time on the world’s most powerful observatories, a hurdle that contributed to the long period of time it took to pin down the moon’s orbit.

“The satellite can be seen only with a telescope like Keck Observatory’s fitted with LSG-AO (laser guide-star adaptive optics), but time on the mighty Keck’s is highly prized and in limited availability,” said Marchis in a SETI Institute news release.

The Keck Observatory, located atop Mauna Kea, Hawaii, consists of two telescopes and in this study, Marchis’ team used the Keck II telescope that is outfitted with a precision adaptive optics system that fires a powerful laser high into the atmosphere, creating an artificial star as seen by the telescope’s optics. The motion of the guide star reveals turbulence in the upper atmosphere (the same effect that causes stars to “twinkle”), which can be actively compensated for, revealing deep space objects that would have otherwise been impossible to resolve from ground-based telescopes.

Two adaptive optics observations made in July 2006 and October 2008 with the Keck II telescope.
The center of each image shows the elongated shape of Hektor. The small, faint moon is shown
in the cyan circle.

Read Full Story: http://news.discovery.com/space/asteroids-meteors-meteorites/bizarre-orbit-of-weird-looking-asteroids-moon-revealed-140227.htm