Featured Research

from universities, journals, and other organizations

First Triple Asteroid System Found

Date:
August 10, 2005
Source:
University of California - Berkeley
Summary:
Using the Very Large Telescope in Chile, UC Berkeley and Paris Observatory astronomers have obtained images of the first triple asteroid system: two moonlets orbiting one of the largest of the main-belt asteroids, Sylvia. A detailed chart of their orbits yields a density for Sylvia, indicating it is a "rubble pile" asteroid probably disrupted by impact long ago and gravitationally re-accreted - except for the two large moons.

Artist's conception shows twin moonlets, Romulus and Remus, orbiting the large main-belt asteroid 87 Sylvia.
Credit: Image courtesy European Southern Observatory

Berkeley -- One of the thousands of asteroids orbiting the sun has been found to have a mini planetary system of its own.

University of California, Berkeley, assistant research astronomerFranck Marchis and his colleagues at the Observatoire de Paris havediscovered the first triple asteroid system - two small asteroidsorbiting a larger one known since 1866 as 87 Sylvia.

Because 87 Sylvia was named after Rhea Sylvia, the mythicalmother of the founders of Rome, Marchis proposed naming the twin moonsafter those founders: Romulus and Remus. The International AstronomicalUnion (IAU) approved the names, to be announced in its Aug. 11circular.

Marchis and his colleagues will report their discovery in theAug. 11 issue of the journal Nature simultaneously with an announcementthat day at theAsteroid Comet Meteor conference in Armação dos Búzios, in the Brazilian state of Rio de Janeiro.

The asteroid 87 Sylvia is one of the largest known from theasteroid main belt, which is located between the orbits of Mars andJupiter. Shaped like a lumpy potato, Sylvia is about 280 kilometers(175 miles) in diameter and is located in the Cybele outer part of thebelt, about 3.5 astronomical units (AU) from the sun. An AU is 93million miles, the average distance between the sun and Earth.

Four years ago, Sylvia was discovered to have a moon, making itone of some 60 known binary asteroids in various asteroid populationsof the solar system. Seventeen of these binary systems are in the mainasteroid belt and have been imaged directly either by adaptive opticssystems on large, ground-based telescopes or by the Hubble SpaceTelescope.

Now, a second moon has been seen around Sylvia, making it atriple asteroid system. Sylvia's newly discovered moons orbit in nearlycircular orbits in the same plane and direction (prograde) as the moonorbits the Earth. The closest moonlet, orbiting about 710 km (450miles) from Sylvia, is Remus, a body only 7 km (4.4 miles) across andcircling Sylvia every 33 hours. The second, Romulus, orbits at about1360 km (860 miles), measures about 18 km (11.3 miles) across, andorbits in 87.6 hours. The asteroid Sylvia spins at a rapid rate, onceevery 5 hours and 11 minutes.

"People have been looking for multiple asteroid systems for along time, because binary asteroid systems in the main belt seem to becommon and formation scenarios, such as a collision between twoasteroids followed by disruption and re-accretion, suggest thatfragments should be orbiting bigger asteroids," Marchis said. "Icouldn't believe we found one."

From two months' of observations of the moonlets' orbits,Marchis and his Paris colleagues were able to precisely calculate themass and density of Sylvia, which shows it to be a "rubble-pile"asteroid, Marchis said. These asteroids are loose aggregations of rockpresumably created when one asteroid smacked into another, disruptingone or both of them. A new asteroid formed later by accretion of largefragments from the disruption. The moonlets probably are debris leftover from the collision that were gravitationally captured by the newlyformed asteroid and which eventually settled into orbits around it.

"That's why most main-belt asteroids with companions have arubble-pile structure," he said. "Because of the scenarios of theirformation, we expect to see more multiple asteroid systems like this."

The density, 1.2 grams per cubic centimeter, is 20 percenthigher than the density of water, which suggests it is composed ofwater, ice and rubble from a primordial asteroid, probably a hydratedcarbonaceous chondrite, based on previous spectroscopic studies of theasteroid.

"It could be up to 60 percent empty space," said astronomer Daniel Hestroffer, one of three coauthors from the Institutde Mécanique Céleste et Calculs d'Éphémérides at the Observatoire deParis.

The discovery was made with one of the European SouthernObservatory's 8-meter telescopes (Yepun) of the Very Large Telescope atCerro Paranal, using the telescope's infrared camera and the highangular resolution provided by the adaptive optics system (NACO). Viathe observatory's promising "service observing mode," Marchis and hiscolleagues were able to obtain sky images of many asteroids over asix-month period without actually having to travel to Chile. DVD dataof the observations were sent regularly via mail to Berkeley.

Marchis had the discovery sitting on his shelf for months,since November 2004, because he waited for the completion of theproject before starting to process the data and before sending them tocolleague Pascal Descamps of the Observatoire de Paris. Just as Marchiswas set to go on vacation in March 2005, Descamps sent him a brief noteentitled "87 Sylvia est triple?" pointing out that he could see twomoonlets around several images of Sylvia. The entire team then focusedquickly on analysis of the data, wrote a paper, submitted an abstractto the August meeting in Rio de Janeiro and submitted a naming proposalto the IAU.

Marchis and his colleagues hope to use the adaptive optics ofthe Keck and the Gemini telescopes to obtain better images of thetriple-asteroid system in order to pin down the precise orbits, verifySylvia's formation scenario and chart the system's evolution. Alreadythey see precession of the moon's orbits resulting from the irregularshape of Sylvia.

The work was partially supported by the National ScienceFoundation and the Technology Center for Adaptive Optics and by theChretien International Research Grant of the American AstronomicalSociety.

The fourth author with Marchis, Descamps and Hestroffer was JérômeBerthier, also of the Institut de Mécanique Céleste et Calculsd'Éphémérides at the Observatoire de Paris. The moon now designatedRomulus was discovered in 2001 by M. E. Brown and J. L. Margot usingthe Keck II telescope atop Mauna Kea in Hawaii.


Story Source:

The above story is based on materials provided by University of California - Berkeley. Note: Materials may be edited for content and length.


Cite This Page:

University of California - Berkeley. "First Triple Asteroid System Found." ScienceDaily. ScienceDaily, 10 August 2005. <www.sciencedaily.com/releases/2005/08/050810135320.htm>.
University of California - Berkeley. (2005, August 10). First Triple Asteroid System Found. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2005/08/050810135320.htm
University of California - Berkeley. "First Triple Asteroid System Found." ScienceDaily. www.sciencedaily.com/releases/2005/08/050810135320.htm (accessed October 22, 2014).

Share This



More Space & Time News

Wednesday, October 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Russian Cosmonauts Kick Off Final Spacewalk of 2014

Russian Cosmonauts Kick Off Final Spacewalk of 2014

Reuters - US Online Video (Oct. 22, 2014) — Russian cosmonauts Maxim Suraev and Alexander Samokutyaev step outside the International Space Station to perform work on the exterior of the station's Russian module. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
Comet Siding Spring Grazes Mars' Atmosphere

Comet Siding Spring Grazes Mars' Atmosphere

Newsy (Oct. 19, 2014) — A comet from the farthest reaches of the solar system passed extremely close to Mars this weekend, giving astronomers a rare opportunity to study it. Video provided by Newsy
Powered by NewsLook.com
Latin America Launches Communications Satellite

Latin America Launches Communications Satellite

AFP (Oct. 17, 2014) — Argentina launches a home-built satellite, a first for Latin America. It will ride a French-made Ariane 5 rocket into orbit, and will provide cell phone, digital TV, Internet and data services to the lower half of South America. Duration: 00:41 Video provided by AFP
Powered by NewsLook.com
This Week @ NASA, October 17, 2014

This Week @ NASA, October 17, 2014

NASA (Oct. 17, 2014) — Power spacewalk, MAVEN’s “First Light”, Hubble finds extremely distant galaxy and more... Video provided by NASA
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins