Bestla (// BEST-lə) or Saturn XXXIX (provisional designation S/2004 S 18) is a retrograde irregular moon 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.
Bestla is about 7 kilometres in diameter, and orbits Saturn at an average distance of 20,192,000 km in 1088 days, at an inclination of 147° to the ecliptic (151° to Saturn's equator), in a retrograde direction and with an eccentricity of 0.5145. Back in 2005, early observations suggested that Bestla had a very high eccentricity of 0.77. Like many of the outer irregular moons of the gas giants, Bestla's eccentricity may vary as a result of the Kozai mechanism.
- Jacobson, R.A. (2007) SAT270, SAT271 (2007-06-28). "Planetary Satellite Mean Orbital Parameters". JPL/NASA. Retrieved 2008-01-19.
- Brian G. Marsden (2005-05-03). "MPEC 2005-J13 : Twelve New Satellites of Saturn". Minor Planet Center. Retrieved 2008-01-19.
- Saturn's Known Satellites (by Scott S. Sheppard)
- Jewitt's New Satellites of Saturn page
- IAUC 8523: New Satellites of Saturn May 4, 2005 (discovery)
- IAUC 8826: Satellites of Jupiter and Saturn April 5, 2007 (naming the moon)