Bestla (moon)

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.

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/
Named after	Bestla
Alternative names	S/2004 S 18
Orbital characteristics[1]
Semi-major axis	20337900 km
Eccentricity	0.461
Orbital period (sidereal)	−1087.46 days
Inclination	136.3°
Satellite of	Saturn
Group	Norse group
Physical characteristics
Dimensions	15.56 × 7 × 5.98 km (modeled)[2]
Mean diameter	7+50% −30% km[3]
Synodic rotation period	−14.6238±0.0001 h[3]
Pole ecliptic latitude	85°+5° −15°[4][a]
Albedo	0.06 (assumed)[3]
Spectral type	g – r = 0.72 ± 0.07, r – i = 0.38 ± 0.07[5]
Apparent magnitude	23.8[4]
Absolute magnitude (H)	14.6[4]

Description

Bestla is about 7 kilometres in diameter, and orbits Saturn at an average distance of 20,337,900 km in 1087 days, at an inclination of 136° to the ecliptic, in a retrograde direction and with an eccentricity of 0.461.^[1] Early observations from 2005 suggested that Bestla had a very high eccentricity of 0.77.^[6] Like many of the outer irregular moons of the giant planets, Bestla's eccentricity may vary as a result of the Kozai mechanism.^{[citation needed]} Bestla rotates in a retrograde direction and makes a full rotation every 14.6238±0.0001 hours.^[3] 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.^[4]

Name

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

Notes

1. Assuming the north pole is the one pointing north of the invariable plane, in accordance with IAU standards.