Helene (moon)

Helene

Saturn's moon Helene in front of Saturn, recorded by the Cassini-Huygens space probe
Provisional or systematic name	S / 1980 S 6
Central body	Saturn
Properties of the orbit
Major semi-axis	377,420 km
Periapsis	374,740 km
Apoapsis	380,100 km
eccentricity	0.0071
Orbit inclination	0.21 °
Orbital time	2.737 d
Mean orbital velocity	10.03 km / s
Physical Properties
Albedo	0.6
Apparent brightness	18.4 mag
Medium diameter	(35.2 ± 0.4) km
Dimensions	≈ 11  ·  10 ¹⁵ kg
Medium density	≈ 0.5 g / cm ³
Sidereal rotation	2.737 days
Axis inclination	0 °
Acceleration of gravity on the surface	≈ 0 m / s ²
Escape speed	≈ 0 m / s
discovery
Explorer	Pierre Laques , Jean Lecacheux
Date of discovery	March 1, 1980
Remarks	Bound rotation

Helene (also Saturn XII) is a small (the seventeenth largest) moon on the planet Saturn .

discovery

Helene was discovered on March 1, 1980 by the astronomers Pierre Laques and Jean Lecacheux at the observatory on the Pic du Midi in the French Pyrenees . It was initially given the provisional designation S / 1980 S 6 . In 1988 she was officially named after Helen of Troy , a granddaughter of Kronos , to whom Saturn corresponds in Roman mythology .

Orbit data

Helene, recorded by Voyager 2 on August 25, 1981

Helene orbits Saturn at an average distance of 377,420 km in 65 hours and 41 minutes. The orbit has an eccentricity of 0.0071 and is inclined 0.21 ° to the equatorial plane of Saturn.

It is one of two small moons on the orbit of the great moon Dione . Helene runs ahead of Dione at an angular distance of 60 ° in the leading Lagrangian point L ₄ . In the following Lagrangian point L ₅ , the moon Polydeuces Dione follows at an angle of 60 °.

Before she got her official name, Helene was commonly referred to as "Dione B".

Structure and physical data

Helene is an irregularly shaped body with an extension of 36 × 32 × 30 km. Its low density of 0.5 g / cm ³ indicates that it is mainly composed of water ice and a small amount of silicate rock.

Helene rotates around her own axis in 65 hours and 41 minutes and thus shows a bound rotation like the Earth's moon . It has a light surface with an albedo of 0.6, i.e. That is, 60% of the incident sunlight is reflected . Seen from earth, it is an extremely faint object with an apparent brightness of 18.4 ^m .

gallery

Helene, taken by Cassini on July 20, 2007 from a distance of 40,211 km.
Helene, taken by Cassini on November 24, 2008 at a distance of 68,000 km
Close-up of Helene, taken by Cassini on March 3rd, 2010.
Helene, recorded by Cassini on March 3rd, 2010.
Helene sickle , taken by Cassini on March 3, 2010
Helene, taken by Cassini on January 31, 2011 from a distance of 31,000 km.
Hemisphere of Helene, taken by Cassini on June 18, 2011.

Individual evidence

^ Cassini Solstice Mission - About Saturn & Its Moons: Helene ( Memento from April 21, 2014 in the Internet Archive ), NASA

Web links

Commons : Helene (Mond) - Collection of images, videos and audio files

IAUC 3457: Saturn March 6, 1980 (discovery)
IAUC 3872: Satellites of Jupiter and Saturn September 30, 1983 (numbering)
IAUC 4609: Satellites of Saturn and Uranus June 8, 1988 (numbering and naming)
Cassini Solstice Mission: Helene
NASA Solar System Exploration - Helene: Facts & Figures (dead link)
JPL - Planetary Satellite Physical Parameters

further inside	Saturn moons	further outside
Dione	Semi- major axis (km) Helene 377.400	Polydeuces

[1] Cassini Solstice Mission - About Saturn & Its Moons: Helene ( Memento from April 21, 2014 in the Internet Archive ), NASA


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