Distant asteroid revealed to be a complex mini geological world

Feb 27, 2014
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 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.

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 and laser guide star system (LGS-AO).

Since then, they collaborated with several researchers from University of California at Berkeley in order 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.

"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," said Matija Cuk, coauthor and scientist at the Carl Sagan Center of the SETI Institute. "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."

Hektor has been known since the 1970s to be spinning rapidly (less than 7 hours) and extremely elongated. Using the high-angular resolution of the Keck II telescope, combined with a large number of photometric observations taken since 1957, the team built a refined shape hoping to get a clue to the origin of the system.

"We built several models of equal quality from the photometric data, but we favored a model made of two lobes since some of the best adaptive optics observations suggest that the Trojan asteroid has a dual structure," said Josef Durech, co-author and researcher at the Charles University in Prague.

A complex shape for the asteroid and a bizarre orbit for the moon will be matters of discussion for the scientific community. The team speculated that the moon could be ejecta produced by a slow encounter that formed the bi-lobed asteroid, but emphasized the need for robust and accurate simulations.

"We also show that Hektor could be made of a mixture of rock and ices, similar to the composition of Kuiper belt objects, Triton and Pluto. How Hektor became a Trojan asteroid, located at only 5 times the Earth–Sun distance, is probably related to the large scale reshuffling that occurred when the were still migrating," said Julie Castillo-Rogez, researcher at the Jet Propulsion Laboratory, California Institute of Technology.

Hektor was discovered in 1907 by August Kopff. The satellite of Hektor, discovered in 2006 by Franck Marchis and his team has not been named yet. The team welcomes any idea for naming the satellite, keeping in mind that the satellite should receive a name closely related to the name of the primary and reflecting the relative sizes between these objects.

The paper entitled "The puzzling mutual 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)

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and world-leading laser guide star adaptive optics systems.

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User comments : 13

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hemitite
5 / 5 (3) Feb 27, 2014
Satellite name: Pup
Maggnus
5 / 5 (5) Feb 27, 2014
Holy complex orbit calculations batfink! Great work!
Captain Stumpy
5 / 5 (3) Feb 27, 2014
The satellite of Hektor, discovered in 2006 by Franck Marchis and his team has not been named yet. The team welcomes any idea for naming the satellite, keeping in mind that the satellite should receive a name closely related to the name of the primary and reflecting the relative sizes between these objects

maybe this is just me, but it seems obvious that the satellite should be named Scamandrius or possibly Astyanax, the infant son of Hektor...
malapropism
5 / 5 (2) Feb 27, 2014
Or, since they appear to be stably co-orbiting, how about Andromache (Hector's wife).
Mimath224
5 / 5 (2) Feb 27, 2014
Or since Paris is mentioned in the article how about 'paris' Hector's younger brother?
Whydening Gyre
5 / 5 (1) Feb 27, 2014
The satellite of Hektor, discovered in 2006 by Franck Marchis and his team has not been named yet. The team welcomes any idea for naming the satellite, keeping in mind that the satellite should receive a name closely related to the name of the primary and reflecting the relative sizes between these objects

maybe this is just me, but it seems obvious that the satellite should be named Scamandrius or possibly Astyanax, the infant son of Hektor...

How bout - Igor...
Captain Stumpy
not rated yet Feb 27, 2014
@malapropism
@Mimath224
@Whydening Gyre
all really great ideas!
I simply suggested the infant son due to the small size of the object in comparison to the asteroid! Given that it is not larger, it just seemed appropriate...
younger bro can be cool too... tagging along looking for trouble
wife would be good too... locked forever in orbit till death due them part
@WG – is that pronounced "EYE"gore? LOL doesnt seem Trojan, but funny!
like I said... all good ideas...Hmm....

@Maggnus or Q-Star
how long do they have? I know the orbits are unstable, but are there any real figures that could be taken into consideration? (other than EU? LMFAO)
Protoplasmix
5 / 5 (1) Feb 27, 2014
Ejecta from a slow encounter would be my guess too. Interesting system.

Name idea: Mirum ("small wonder" in Latin) or Mirumus Hektor.
Mimath224
5 / 5 (1) Feb 28, 2014
@Captain Stumpy according to the NASA surface spectroscopy section '...624 Hektor is unexplainable by current modeling methods...' so it would take someone like Q-Star active in the field to asnwer your question. According to some 2 body method simulation the orbits breakdown in about a decade or so but then I feel sure with more research that model could be made more accurate.
Mimath224
5 / 5 (1) Feb 28, 2014
whoops sorry, comment appeared twice so have deleted one
imbalzanog
not rated yet Feb 28, 2014
Mi piace ricordare che il primo sistema di pianetini a coppia fu scoperto nel '900 da alcuni miei amici astronomi dell'Osservatorio di Pino Torinese; avevo proposto ancor prima della scoperta di dare il noome Fermat-Imbalzano alla coppia, ma non se ne ricordarono più... oh tempora, oh mores! G. Imbalzano, unico autore della dimostrazione del II Teorema di Fermat, presentato a livello accademico ben prima di successivi annunci eclatanti ed errati. http://www.lulu.c...968.html
Mimath224
5 / 5 (1) Feb 28, 2014
@imbalzanog lingua Italiana non è buona. soluzione di Fermat per asteroide coppia in 900 ". Probabilmente mi sbaglio! Si prega di scrivere in inglese
My Italian language is not good. I read 'you discovered solution to Fermat function for asteroid pair in 900'. I must be wrong! Please write again in English
cantdrive85
not rated yet Mar 02, 2014
Mi piace ricordare che il primo sistema di pianetini a coppia fu scoperto nel '900 da alcuni miei amici astronomi dell'Osservatorio di Pino Torinese; avevo proposto ancor prima della scoperta di dare il noome Fermat-Imbalzano alla coppia, ma non se ne ricordarono più... oh tempora, oh mores! G. Imbalzano, unico autore della dimostrazione del II Teorema di Fermat, presentato a livello accademico ben prima di successivi annunci eclatanti ed errati. http://www.lulu.c...968.html

¿Que?