Greip 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° 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.
Greip has a mean radius of about 3.0 km, assuming an albedo of 0.04. It orbits Saturn at an inclination of about 173° and an eccentricity of about 0.3. At a mean distance of 18.4 million km from Saturn, the satellite takes about 936 Earth days to complete one orbit.
Greip was discovered on 6 March 2006 by Scott S. Sheppard, David C. Jewitt and Jan T. Kleyna using the Subaru 8.3-m reflector telescope on Mauna Kea, Hawaii.
How Greip Got its Name:
Originally called S/2006 S4, Greip was named for one of the nine giantesses who gave birth to Heimdall, the guard of the rainbow bridge that links our world to Asgard, home of the Norse gods.