Ymir 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.
Ymir and another member of the Norse group, Skathi, may be the sources of material that coats the dark side of Iapetus and, to a lesser extent, the surface of Hyperion.
Ymir has a mean radius of about 9 km, assuming an albedo of 0.06. It orbits Saturn at an inclination of about 172 degrees and an eccentricity of about 0.3. At a mean distance of 23.1 million km from Saturn, the satellite takes about 1,316 Earth days to complete one orbit.
Ymir 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 at the European Southern Observatory in La Silla, Chile. They discovered Paaliaq and Kiviuq of the Inuit group at the same time.
How Ymir Got its Name:
Originally called S/2000 S1, Ymir was named for the first living being in Norse mythology, the first of a race of frost giants. Odin and his brothers killed Ymir and used his body parts to fashion the Earth. His skull became the heavens.