Thrymr 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, Suttungr, Skathi, Siarnaq, Erriapus, and Mundilfari.
Thrymr has a mean radius of 2.2 miles (3.5 kilometers), assuming an albedo (a measure of how reflective the surface is) of 0.06. It orbits Saturn at an inclination of about 174 degrees and an eccentricity of about 0.5. At a mean distance of 12.7 million miles (20.4 million kilometers) from Saturn, the moon takes about 1,094 Earth days to complete one orbit.
Thrymr 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. Thrymr and the other Norse moons also have eccentric orbits, meaning they are more elongated than circular.
Like Saturn's other irregular moons, Thrymr 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.
How Thrymr Got Its Name
Originally called S/2000 S7, Thrymr was named for a giant in Norse mythology who stole Thor's hammer and offered to return it only if the gods gave him the very beautiful goddess Freyia to be his wife. The gods agree, but instead send Thor, disguised as Freyia. Thor as Freyia orders the hammer to be placed on "her" knee, whereupon Thor uses the hammer to kill Thrymr, along with the giant's sister, who had asked for "Freyia's" rings.
It was first called Thrym, but the International Astronomical Union Working Group on Planetary System Nomenclature later decided to add the nominative case ending -r to the root Thrym