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87 Sylvia: Asteroids
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Asteroid 87 Sylvia, known since 2001 to be part of a double system, has just gotten more interesting. A team of astronomers at the University of California at Berkeley and the Observatoire de Paris have now established that the asteroid is actually part of a triple system, the first ever discovered. Using data from the European Southern Observatory’s Very Large Telescope array in Chile, the team found two small moons in nearly circular orbits.
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Called 87 Sylvia, the 280-kilometre-wide, potato-shaped asteroid lies about 3.5 times further from the Sun than the Earth does. Astronomers discovered an 18-km-wide moon orbiting it at a distance of about 1360 km in 2001. The newly found moon lies about twice as close to Sylvia, at a distance of 710 km, and measures just 7 km across.
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The asteroid 87 Sylvia is one of the largest known from the asteroid main belt, and is located about 3.5 times further away from the Sun than the Earth, between the orbits of Mars and Jupiter. The wealth of details provided by the NACO images show that 87 Sylvia is shaped like a lumpy potato, measuring 380 x 260 x 230 km (see ESO PR Photo 25a/05). It is spinning at a rapid rate, once every 5 hours and 11 minutes.
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Descamps, P., Hestroffer, D. et al., “Discovery of the first triple asteroidal system 87 Sylvia,” Nature 436 (August 11, 2005), pp. 822-824. available, and so is this release from UC-Berkeley, which contains links to some interesting animations of the triple system.
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This article focuses on research on the asteroid 87 Sylvia. Among the thousands of asteroids roaming the inner solar system, 87 Sylvia stands out. New observations reveal that two smaller asteroids orbit this 280-kilometer-wide rock. It's the first asteroid found to be accompanied by two moons. More than just a curiosity, the tiny moons have enabled researchers to determine the mass and density of 87 Sylvia. Like some other asteroids, the rock turns out to be extraordinarily porous, with up to 60 percent of its interior composed of empty space, report Franck Marchis of the University of California, Berkeley and his colleagues.
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Photograph of the asteroid 87 Sylvia, recorded Aug. 9, 2004, using the Very Large Telescope at Cerro Paranal of the European Southern Observatory, shows a pair of smaller moonlets to the left of the primary body. Image Credit: Franck Marchis/UC Berkeley and VLT
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