Post by Chicago Astronomer - Astro Joe on Aug 10, 2005 13:52:16 GMT -6
First triple asteroid system found
University of California, Berkeley, assistant research astronomer Franck Marchis and his colleagues at the Observatoire de Paris have discovered the first triple asteroid system - two small asteroids orbiting a larger one known since 1866 as 87 Sylvia.
Because 87 Sylvia was named after Rhea Sylvia, the mythical mother of the founders of Rome, Marchis proposed naming the twin moons after those founders: Romulus and Remus. The International Astronomical Union (IAU) approved the names, to be announced in its Aug. 11 circular.
Marchis and his colleagues will report their discovery in the Aug. 11 issue of the journal Nature simultaneously with an announcement that day at the Asteroid 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 the asteroid main belt, which is located between the orbits of Mars and Jupiter. Shaped like a lumpy potato, Sylvia is about 280 kilometers (175 miles) in diameter and is located in the Cybele outer part of the belt, about 3.5 astronomical units (AU) from the sun. An AU is 93 million miles, the average distance between the sun and Earth.
Four years ago, Sylvia was discovered to have a moon, making it one of some 60 known binary asteroids in various asteroid populations of the solar system. Seventeen of these binary systems are in the main asteroid belt and have been imaged directly either by adaptive optics systems on large, ground-based telescopes or by the Hubble Space Telescope.
Now, a second moon has been seen around Sylvia, making it a triple asteroid system. Sylvia's newly discovered moons orbit in nearly circular orbits in the same plane and direction (prograde) as the moon orbits the Earth. The closest moonlet, orbiting about 710 km (450 miles) from Sylvia, is Remus, a body only 7 km (4.4 miles) across and circling Sylvia every 33 hours. The second, Romulus, orbits at about 1360 km (860 miles), measures about 18 km (11.3 miles) across, and orbits in 87.6 hours. The asteroid Sylvia spins at a rapid rate, once every 5 hours and 11 minutes.
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This is quite interesting.