Hyrrokkin 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. Hyrrokkin appears to be a member of a subgroup that also includes Skathi, Skoll, S/2006 S1, Bergelmir, Farbauti, S/2006 S3, and Kari.
Hyrrokkin has a mean radius of about 3 km, assuming an albedo of 0.04. It orbits Saturn at an inclination of about 151° and an eccentricity of about 0.3. At a mean distance of 18.4 million km from Saturn, the satellite takes about 932 Earth days to complete one orbit.
Hyrrokkin was discovered on 12 December 2004 by Scott S. Sheppard, David C. Jewitt and Jan T. Kleyna using the Subaru 8.3-m reflector telescope on Mauna Kea, Hawaii.
How Hyrrokkin Got its Name:
Originally called S/2004 S19, Hyrrokkin was named for giantess in Norse mythology who launched Baldur's enormous funeral ship with one mighty push when the gods, themselves, were unable to budge it.