Erriapus 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 degrees 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, Bebhionn and Tarvos.
Observations by Tommy Grav and James Bauer using telescopes on Mauna Kea, Hawaii in 2006 found that the color of Albiorix varies over its surface. They hypothesize that Tarvos and Erriapus, which were both seen to be light red, are the largest fragments from an impact on Albiorix, leaving a less-red crater. (These observations did not include Bebhionn.)
Erriapus has a mean radius of about 5 km assuming an albedo of 0.06. At a mean distance of 17.6 million km from Saturn, the satellite takes about 871 Earth days to complete one orbit.
Erriapus was discovered 23 September 2000 by Brett J. Gladman, John J. Kavelaars, Jean-Marc Petit, Hans Scholl, Matthew J. Holman, Brian G. Marsden, Phillip D. Nicholson, and Joseph A. Burns at the Mauna Kea Observatory on the island of Hawaii.
How Erriapus Got its Name:
Moons of Saturn were originally named for Greco-Roman Titans and descendants of the Titans. But as many new moons were discovered scientists began selecting names from more mythologies, including Gallic, Inuit and Norse stories.
Erriapus, originally designated S/2000 10, is named for a Gallic giant.