Bebhionn is one of the four known members of the Gallic group of moons, which orbit Saturn at a mean distance of 16 to 19 million km, at inclinations between 35° and 40° from the plane of Saturn's equator, and with eccentricities around 0.53. (A satellite's eccentricity is a number between 0 and 1 which describes the shape of the orbit. The closer to 0, the more circular it is; the closer to 1, the more elongated.)
The Gallic moons all have prograde orbits (they travel around Saturn in the same direction as the planet's rotation), but their deviations from circular orbits and from the plane of Saturn's equator classify them as "irregular" satellites. Like Saturn's other irregular moons, they are thought to be objects that were captured by Saturn's gravity, rather than having accreted from the dusty disk that surrounded the newly formed planet, as the regular satellites are thought to have done.
The similarities among the orbits of moons in the Gallic group suggest a common origin -- they may be fragments of a single object that shattered in a collision. The other members of this group are Albiorix, Erriapus and Tarvos.
Bebhionn has a mean radius of about 3 km, assuming an albedo of 0.04. At a mean distance of 17.1 million km from Saturn, the satellite takes about 835 Earth days to complete one orbit.
Discovery:
Bebhionn was discovered on 12 December 2004 by Scott S. Sheppard, David C. Jewitt and Jan T. Kleyna, using the wide-field camera on the 8.2-m Subaru telescope on Mauna Kea, Hawaii, with orbital elements computed by Brian Marsden.
How Bebhionn Got its Name:
Originally called S/2004 S11, Bebhionn was named for a beautiful giantess in Celtic mythology. In one story, she escapes from Maidens' Land, which was populated entirely by women except for the king and his three sons, only to be slain by her giant husband, who was the son of the king of the Isle of Men.
