SETI HEKTOR: Distant asteroid, a complex mini geological world

Artistic representation of the Trojan system showing the large 250 km dual shape Hektor and its 12 km moon. 

Credit: H. Marchis & F. Marchis

After 8 years of observations, scientists from the SETI Institute have found an exotic orbit for the largest Trojan asteroid, (624) Hektor, the only one known to possess a moon.

The formation of this system made of a dual primary and a small moon is still a mystery, but they found the asteroid could be a captured Kuiper body product of the reshuffling of giant planets in our solar system.

The results are being published today in Astrophysical Letters.

This study, based on W. M. Keck Observatory data and photometric observations from telescopes throughout the world, suggests that the asteroid and its moon are products of the collision of two icy asteroids.

This work sheds light on the complex youth of our solar system, when the building blocks that formed the core of Giant planets and their satellites were tossed around or captured during the giant planet migrations.

Franck Marchis

In 2006, a small team of astronomers led by Franck Marchis, astronomer at the Carl Sagan center of the SETI Institute, detected the presence of a small 12 km diameter moon around the large Trojan asteroid (624) Hektor using the 10 m Keck II telescope atop Mauna Kea, fitted with the NIRC-2 (Near-Infrared Camera 2) instrument behind the adaptive optics and laser guide star system (LGS-AO).

Since then, they collaborated with several researchers from University of California at Berkeley to determine the orbit of this moon and understand the origin of the system.

Trojan asteroids are those that are temporarily trapped in regions 60 degrees in front or 60 degrees behind the planet Jupiter in its orbit around the Sun. They are difficult to study since they are small and faint.

While the asteroid has been studied for 8 years, there were a couple of significant challenges before a paper could be published, according to Marchis.

"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," he said.

"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."

The research, conducted with expert assistance from colleagues at the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) of the Observatoire de Paris, revealed that the 12 km moon orbits the large 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.

More Information: "The puzzling mutual orbit of the binary Trojan asteroid (624) Hektor" published today by ApJL is co-authored by F. Marchis (SETI Institute), J. Durech (Charles University), J. Castillo-Rogez (Jet Propulsion Laboratory), F. Vachier (IMCCE-Obs. De Paris), M. Cuk (SETI Institute), J. Berthier (IMCCE-Obs. De Paris), M.H. Wong (UC Berkeley), P. Kalas (UC Berkeley), G. Duchene (UC Berkeley), M. A. van Dam (Flat Wavefronts), H. Hamanowa (Hamanowa observatory)and M. Viikinkoski (Tampere University) arxiv.org/ftp/arxiv/papers/1402/1402.7336.pdf