Discovered in 1866,
asteroid 87 Sylvia lies
3.5 AU from the Sun, between the orbits of Mars and Jupiter.
Also shown in recent years to be one in a growing list of
double asteroids, new observations
during August and
October 2004 made at the
Paranal Observatory convincingly
demonstrate that 87 Sylvia in fact has two moonlets - the
first known triple asteroid system.
At the center of this composite of the image data, potato-shaped
itself is about 380 kilometers wide.
data show inner moon, Remus,
orbiting Sylvia at a distance of about 710 kilometers
once every 33 hours, while
outer moon Romulus orbits at 1360 kilometers in 87.6 hours.
Tiny Remus and Romulus are 7 and 18 kilometers across respectively.
Because 87 Sylvia was named after
Silvia, the mythical mother
of the founders of Rome,
the discoverers proposed Romulus and
Remus as fitting names for the two moonlets.
The triple system is thought to be the not uncommon result of
collisions producing low density,
pile asteroids that are loose aggregations of debris.