Helene (moon)

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Helene
Helene over Saturn.jpg
Cassini image of Helene against the backdrop of Saturn's clouds (March 3, 2010)
Discovery
Discovered by Laques and
Lecacheux
Discovery site Pic du Midi Observatory
Discovery date March 1, 1980
Designations
Alternative names
  • Helene
  • Dione B
  • Saturn XII (12)
  • S/1980 S 6
Orbital characteristics
Semi-major axis 377396 km
Eccentricity 0.0022
Orbital period 2.736915 d[1]
Inclination 0.199° (to Saturn's equator)
Satellite of
Physical characteristics
Dimensions 43.4 × 38.2 × 26 km [2]
Mean radius 17.6±0.4 km[2]
Albedo 1.67±0.20 (geometric) [3]

Helene (/ˈhɛlɨn/ HEL-ə-nee;[a] Greek: Ἑλένη) is a moon of Saturn. It was discovered by Pierre Laques and Jean Lecacheux in 1980 from ground-based observations at Pic du Midi Observatory, and was designated S/1980 S 6.[4] In 1988 it was officially named after Helen of Troy, who was the granddaughter of Cronus (Saturn) in Greek mythology.[5] Helene is also designated Saturn XII (12), which it was given in 1982, and Dione B,[b] because it is co-orbital with Dione and located in its leading Lagrangian point (L4). It is one of four known trojan moons.

Exploration[edit]

Helene was initially observed from Earth in 1980,[4] and Voyager flybys of Saturn in the early 1980s allowed much closer views. The Cassini–Huygens mission, which went into orbit around Saturn in 2004, provided still better views, and allowed more in-depth analysis of Helene, including views of the surface under different lighting conditions. Some of the closest images of Helene to date are from the Cassini spacecraft's 1800 km flyby on March 3, 2010, and another very successful imaging sequence occurred in June 2011. There have been many other approaches over the course of the Cassini mission, and future flybys may yield additional data.

Selected observations[edit]

Mostly raw greyscale images with near infrared or ultraviolet channels.

High-resolution view of leading hemisphere, showing gullies and apparent dust (regolith) flows (Cassini, June 2011)
Flow-like features on Helene's leading hemisphere (Cassini, January 2011)
Helene's Saturn-facing side, lit by saturnshine (Cassini, March 2010)
Close-up of Helene with Saturn in the background (Cassini, March 2010)
Cassini image from March 3, 2010
Cassini orbiter image from November 2008
Cassini image taken July 2007
Voyager 2 image (August 1981)

References[edit]

Notes

  1. ^ /ˈhɛlɨn/ HEL-ə-nee is the regular pronunciation, as expected from the Greek etymology, but /hɨˈln/ hə-LEE-nee and /hɨˈln/ hə-LEEN are also heard. The Modern Greek pronunciation is e-LAY-nee.
  2. ^ Transactions of the International Astronomical Union, Vol. XVIIIA, 1982 (mentioned in IAUC 3872: Satellites of Jupiter and Saturn, September 30, 1983)

Citations

Sources

External links[edit]