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Helene (moon)

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Helene
Helene over Saturn (color).jpg
Cassini image of Helene against the backdrop of Saturn's clouds (March 3, 2010)
Discovery
Discovered byLaques and
Lecacheux[1]
Discovery sitePic du Midi Observatory
Discovery dateMarch 1, 1980
Designations
  • Helene
  • Dione B
  • Saturn XII (12)
  • S/1980 S 6
Orbital characteristics
377396 km
Eccentricity0.0022
2.736915 d[2]
Inclination0.199° (to Saturn's equator)
Satellite of
Physical characteristics
Dimensions43.4 × 38.2 × 26 km [3]
Mean radius
17.6±0.4 km[3]
Albedo1.67±0.20 (geometric) [4]

Helene (/ˈhɛləni/ 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,[1] and was designated S/1980 S 6.[5] In 1988 it was officially named after Helen of Troy, who was the granddaughter of Cronus (Saturn) in Greek mythology.[6] 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,[5] 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.

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. ^ /ˈhɛləni/ HEL-ə-nee is the regular pronunciation, as expected from the Greek etymology, but /həˈlni/ hə-LEE-nee and /həˈln/ hə-LEEN are also heard. The Modern Greek pronunciation is el-AY-nee.[needs Modern Greek IPA]
  2. ^ Transactions of the International Astronomical Union, Vol. XVIIIA, 1982 (mentioned in IAUC 3872: Satellites of Jupiter and Saturn, September 30, 1983)

Citations

Sources

  • Lecacheux, Jean. (July 1980). "A new satellite of Saturn: Dione B" (discovery). Icarus. 43 (1). Bibcode:1980Icar...43..111L. doi:10.1016/0019-1035(80)90093-7. Retrieved 2016-05-01.
  • Marsden, Brian G. (July 31, 1980). "Satellites of Saturn" (discovery). IAU Circular. 3496. Retrieved 2011-12-23.
  • Marsden, Brian G. (September 30, 1983). "Satellites of Jupiter and Saturn". IAU Circular. 3872. Retrieved 2011-12-23.
  • Marsden, Brian G. (June 8, 1988). "Satellites of Saturn and Uranus" (naming). IAU Circular. 4609. Retrieved 2011-12-23.
  • Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). Icarus. 208 (1): 395–401. Bibcode:2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025.
  • Verbiscer, A.; French, R.; Showalter, M.; Helfenstein, P. (9 February 2007). "Enceladus: Cosmic Graffiti Artist Caught in the Act". Science. 315 (5813): 815. Bibcode:2007Sci...315..815V. doi:10.1126/science.1134681. PMID 17289992. Retrieved 20 December 2011. (supporting online material, table S1)

External links[edit]