Bestla

Bestla imaged by the Cassini spacecraft in September 2015
Discovery
Discovered by	Scott S. Sheppard David C. Jewitt Jan T. Kleyna Brian G. Marsden
Discovery date	2004
Designations
Designation	Saturn XXXIX
Pronunciation	/ˈbɛstlə/
Alternative names	S/2004 S 18
Orbital characteristics [1]
Semi-major axis	20129000 km
Eccentricity	0.521
Orbital period (sidereal)	−1083.6 days
Inclination	145.2°
Satellite of	Saturn
Group	Norse group
Physical characteristics
Mean diameter	7+50% −30% km[2]
Synodic rotation period	14.6238±0.0001 h[2]
Apparent magnitude	23.8

Bestla /ˈbɛstlə/ or Saturn XXXIX 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 4 May 2005, from observations taken between 13 December 2004 and 5 March 2005.

Description

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.^[3] Early observations from 2005 suggested that Bestla had a very high eccentricity of 0.77.^[4] Like many of the outer irregular moons of the giant planets, Bestla's eccentricity may vary as a result of the Kozai mechanism. Bestla's rotation period is 14.6238±0.0001 hours.^[2] Like Kiviuq, it is likely to be a contact binary or binary object, as its light curve has strong variation in brightness and a plateau-like maximum not seen in the other irregulars.^[5]

Name

This moon was named in April 2007 after Bestla, a frost giantess from Norse mythology, who is a mother of Odin.