Tarvos (tar'-vohs) is a natural satellite of Saturn. It was discovered by John J. Kavelaars, et al. in 2000, and given the temporary designation S/2000 S 4. The name is Celtic (Gaulish). Tarvos is about 13 kilometers in diameter, and orbits Saturn at an average of 18,239,000 kilometers. It is also designated as Saturn XXI.