The moonlets of asteroid 87 Sylvia: Remus and Romulus |
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The moonlets of asteroid 87 Sylvia: Remus and Romulus
One of the thousands of small planets orbiting the Sun has been found to have a mini planetary system of its own. A team of researchers, with among them some astronomers from Paris Observatory, have discovered the first triple asteroid system - two small asteroids orbiting a larger one known since 1866 as 87 Sylvia.
One of the images of the discovery taken on August 9, 2004 in K band.
(Credit : Marchis et al., 2005, Nature, UCB/IMCCE-Observatoire de Paris)
Right: artist view of the Sylvia' system (crédit ESO)
The discovery was reported in the August 11 issue of the journal Nature, simultaneously with an announcement that day at the Asteroid Comet Meteor conference in Armação dos Búzios, Rio de Janeiro state, Brazil (IAU Symposium #229).
The discovery was made with Yepun, one of ESO's 8.2-m telescopes of the Very Large Telescope Array at Cerro Paranal (Chile), using the outstanding image' sharpness provided by the adaptive optics NACO instrument. Because 87 Sylvia was named after Rhea Sylvia, the mythical mother of the founders of Rome, the team proposed naming the twin moons after those founders: Romulus and Remus. The International Astronomical Union approved the names.
Successive positions of the moonlet between August and October 2004.
The 280km in size asteroid 87 Sylvia is clearly resolved and is shown enlarged.
(Crédit : Marchis et al., 2005, Nature, UCB/IMCCE-Observatoire de Paris)
Sylvia's moons are considerably smaller, orbiting in nearly circular orbits and in the same plane and direction. The closest and newly discovered moonlet, orbiting about 710 km from Sylvia, is Remus, a body only 7 km across and circling Sylvia every 33 hours. The second, Romulus, orbits at about 1360 km in 87.6 hours and measures about 18 km across. 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 and spinning at a rapid rate, once every 5 hours and 11 minutes.The observations of the moonlets' orbits allow the astronomers to precisely calculate the mass and density of Sylvia. With a density only 20% higher than the density of water, it is likely composed of water ice and rubble from a primordial asteroid. These asteroids are loose aggregations of rock presumably created when another asteroid smacked into it and disrupted it. A new asteroid formed later by accumulation of large fragments. The moonlets are probably debris left over from the collision that were captured by the newly formed asteroid and eventually settled into orbits around it. Because of the way they form, we expect to see more multiple asteroid systems like this.
French team:
Pascal Descamps, Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris
Daniel Hestroffer, Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris
Jérôme Berthier, Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris
American team:
Franck Marchis, University of California at Berkeley, Department of Astronomy
References
(1) F. Marchis, P. Descamps, D. Hestroffer, J. Berthier ; Discovery of the first triple asteroidal system 87 Sylvia. Nature, 2005
See the ESO Press Release
Contacts
Pascal Descamps (Observatoire de Paris, IMCCE) descamps@imcce.fr
Daniel Hestroffer (Observatoire de Paris, IMCCE) hestroffer@imcce.fr
Jérôme Berthier (Observatoire de Paris, IMCCE) berthier@imcce.fr
