Erriapus was discovered on Sept. 23, 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.


Erriapus has a mean radius of 3.1 miles (5 kilometers) assuming an albedo (a measure of how reflective the surface is) of 0.06. At a mean distance of 10.9 million miles (17.6 million kilometers) from Saturn, the moon takes about 871 Earth days to complete one orbit.

Erriapus 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, 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.)

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. It was named Erriapo in August 2003, but the name was changed from Erriapo to the nominative Erriapus per International Astronomical Union conventions in late 2007.

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