Hyrrokkin was discovered on Dec. 12, 2004 by Scott S. Sheppard, David C. Jewitt and Jan T. Kleyna using the Subaru 8.3-m reflector telescope on Mauna Kea, Hawaii.
Hyrrokkin has a mean radius of 1.9 miles (3 kilometers), assuming an albedo (a measure of how reflective the surface is) of 0.04. It orbits Saturn at an inclination of about 151 degrees and an eccentricity of about 0.3. At a mean distance of 11.5 million miles (18.4 million kilometers) from Saturn, the moon takes about 932 Earth days to complete one orbit.
Hyrrokkin is a member of the Norse group of moons. These "irregular" moons have retrograde orbits around Saturn -- traveling around in the opposite direction from the planet's rotation. Hyrrokkin and the other Norse moons also have eccentric orbits, meaning they are more elongated than circular.
Like Saturn's other irregular moons, Hyrrokkin is thought to be an object that was 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. Hyrrokkin appears to be a member of a subgroup that also includes Skathi, Skoll, S/2006 S1, Bergelmir, Farbauti, S/2006 S3, and Kari.
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