Fenrir , or Saturn XLI (provisional designation S/2004 S 16), is a natural satellite of Saturn. Its discovery was announced by Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden on May 4, 2005, from observations taken between December 13, 2004, and March 5, 2005. Fenrir has an apparent magnitude of 25, making it one of the faintest known moons in the Solar System, and was discovered using some of the largest telescopes in the world. Fenrir was named after Fenrir, a giant wolf from Norse mythology, father of Hati and Skoll, son of Loki, destined to break its bonds for Ragnarök.
Fenrir is about 4 kilometres in diameter,