Discovery of the First Triple Asteroidal System

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 led by F. Marchis (UC-Berkeley) with several astronomers from Paris Observatory, have discovered the first triple asteroid system - two small asteroids orbiting a larger one known since 1866 as 87 Sylvia.

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.

Fig1: Image 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. (Courtesy Franck Marchis/UC Berkeley)

(click for high-res annodated version)

Fig 2: Composite image showing the positions of S/2001 (87)1 (called Romulus, the outermost moonlet) and S/2004 (87)1 (called Remus, the innermost moonlet) observed in Aug. and Sept. 2004. The dashed lines correspond to the moonlet orbits. The inset contains a close-up of the primary (Courtesy Franck Marchis/UC Berkeley)

Fig. 3: Artist's conception shows twin moonlets, Romulus and Remus, orbiting the large main-belt asteroid 87 Sylvia. A movie (QuickTime, 8MB) is available on the ESO and UC-Berkeley web sites. (Image courtesy European Southern Observatory).

Press-Releases:

• First Triple Asteroid System Found (UC-Berkeley)
• Rubble-Pile Minor Planet Sylvia and Her Twins (ESO)
• The moonlets of asteroid 87 Sylvia: Remus and Romulus (Observatoire de Paris)