Asteroid 87 Sylvia was discovered by N. R. Pogson on May 16, 1866 from Madras (Chennai), India.
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Title: On the Stability of the Satellites of Asteroid 87 Sylvia
Authors: O. C. Winter, L.A.G. Boldrin, E. Vieira Neto, R. Vieira Martins, S.M. Giuliatti Winter, R. S. Gomes, F. Marchis, P. Descamps

The triple asteroidal system (87) Sylvia is composed of a 280-km primary and two small moonlets named Romulus and Remus (Marchis et al 2005). Sylvia is located in the main asteroid belt. The satellites are in nearly equatorial circular orbits around the primary. In the present work we study the stability of the satellites Romulus and Remus, in order to identify the effects and the contribution of each perturber. The results from the 3-body problem, Sylvia-Romulus-Remus, show no significant variation of their orbital elements. However, the inclinations of the satellites present a long period evolution, when the Sun is included in the system. Such amplitude is amplified when Jupiter is included. An analysis of these results show that Romulus and Remus are librating in a secular resonance and their longitude of the nodes are locked to each other. The satellites get caught in an evection resonance with Jupiter. However, the orbital evolutions of the satellites became completely stable when the oblateness of Sylvia is included in the simulations.

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The magnitude of (87) Sylvia will show a drop of 5% in its light curve due to mutual occultation, eclipse events, which would be detectable with amateur photometry.
The next mutual event will occur in summer 2008.

The discovery was made with one of the European Southern Observatory's 8-meter telescopes (Yepun) of the Very Large Telescope at Cerro Paranal, using the telescope's infrared camera and the high angular resolution provided by the adaptive optics system (NACO).
Via the observatory's promising "service observing mode," Marchis and his colleagues were able to obtain sky images of many asteroids over a six-month period without actually having to travel to Chile. DVD data of 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 the project before starting to process the data and before sending them to colleague Pascal Descamps of the Observatoire de Paris. Just as Marchis was set to go on vacation in March 2005, Descamps sent him a brief note entitled "87 Sylvia est triple?" pointing out that he could see two moonlets around several images of Sylvia.
The entire team then focused quickly on analysis of the data, wrote a paper, submitted an abstract to the August meeting in Rio de Janeiro and submitted a naming proposal to the IAU.

Marchis and his colleagues hope to use the adaptive optics of the Keck and the Gemini telescopes to obtain better images of the triple-asteroid system in order to pin down the precise orbits, verify Sylvia's formation scenario and chart the system's evolution. Already they see precession of the moon's orbits resulting from the irregular shape of Sylvia.
The work was partially supported by the National Science Foundation and the Technology Centre for Adaptive Optics and by the Chretien International Research Grant of the American Astronomical Society.

The fourth author with Marchis, Descamps and Hestroffer was Jerome Berthier, also of the Institut de Mecanique Celeste et Calculs d'Ephemerides at the Observatoire de Paris. The moon now designated Romulus was discovered in 2001 by M. E. Brown and J. L. Margot using the Keck II telescope atop Mauna Kea in Hawaii.

Animation of apparent orbits of Romulus and Remus (2.9 Mb .MPG file)

Animated artist's rendering of asteroids (8 Mb .MOV file)


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