Mundilfari is a member of the Norse group of moons, which orbit Saturn at mean distances ranging from 12 to 24 million km, at inclinations between 136 and 176 degrees from the plane of Saturn's equator, and with eccentricities between 0.12 and 0.77. (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 Norse moons all have retrograde orbits (they travel around Saturn in the opposite direction from the planet's rotation). That and 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.
Unlike the Gallic and Inuit groups of Saturn's moons, the wide range of distances, inclinations and eccentricities among moons in the Norse group suggest that they are not the pieces of a single original object that shattered in a collision, but they may be the pieces of several such "original" objects.
Mundilfari has a mean radius of about 3.5 km, assuming an albedo of 0.06. It orbits Saturn at an inclination of about 169 degrees and an eccentricity of about 0.2. At a mean distance of 18.7 million km from Saturn, the satellite takes about 953 Earth days to complete one orbit.
Discovery:
Mundilfari was discovered in 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 using the 3.6-m Canada-France-Hawaii reflector on Mauna Kea in Hawaii, with adaptive optics. They discovered seven other Saturnian moons at the same time: Tarvos, Ijiraq, Thrymr, Skathi, Siarnaq, Erriapus, and Suttungr.
How Mundilfari Got its Name:
Originally called S/2000 S9, Mundilfari was named for the father of two beautiful children in Norse mythology, a son whom he named "Moon" and a daughter whom he named "Sun." The gods were angered at what they considered his arrogance, so they placed the children in the sky and made the daughter drive the chariot of the sun and the son drive the chariot of the Moon. Each is chased by a wolf who is destined to catch and devour them at the doomsday time known as Ragnarok.
