Bebhionn was discovered on Dec. 12, 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.
Bebhionn has a mean radius of 1.9 miles (3 km), assuming an albedo (a measure of how reflective the surface is) of 0.04. At a mean distance of 10.6 million miles (17.1 million km) from Saturn, the moon takes about 835 Earth days to complete one orbit.
Bebhionn is one of the four known members of the Gallic group of moons. These moons have prograde orbits (they travel around Saturn in the same direction as the planet's rotation), but their egg-shaped, angled orbits classify them as "irregular" moons. 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 moons 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.
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.