Helene (moon)
Cassini image of Helene against the backdrop of Saturn's clouds (March 3, 2010)
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Discovery
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| Discovered by | Laques and Lecacheux |
| Discovery site | Pic du Midi Observatory |
| Discovery date | March 1, 1980 |
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Designations
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| Semi-major axis | 377,396 km |
| Eccentricity | 0.0022 |
| Orbital period | 2.736915 d [1] |
| Inclination | 0.199° (to Saturn's equator) |
| Satellite of | |
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Physical characteristics
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| Dimensions | 43.4×38.2×26 km [2] |
| Mean radius | 17.6 ± 0.4 km [2] |
| Albedo | 1.67 ± 0.20 (geometric) [3] |
Helene (
/ˈhɛlɨniː/ 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] The moon is also designated Saturn XII (12), a number which it received in 1982, under the designation 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.
[edit] Exploration
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 the moon, 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.
[edit] Selected observations
Mostly raw greyscale images with near infrared or ultraviolet channels.
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[edit] References
Notes
- ^ /ˈhɛlɨniː/ hel-ə-nee is the regular pronunciation, as expected from the Greek etymology, but /hɨˈliːniː/ hə-lee-nee and /hɨˈliːn/ hə-leen are also heard.
- ^ Transactions of the International Astronomical Union, Vol. XVIIIA, 1982 (mentioned in IAUC 3872: Satellites of Jupiter and Saturn, September 30, 1983)
Citations
Sources
- Marsden, Brian G. (July 31, 1980). "Satellites of Saturn" (discovery). IAU Circular 3496. http://www.cbat.eps.harvard.edu/iauc/03400/03496.html. Retrieved 2011-12-23.
- Marsden, Brian G. (September 30, 1983). "Satellites of Jupiter and Saturn". IAU Circular 3872. http://www.cbat.eps.harvard.edu/iauc/03800/03872.html. Retrieved 2011-12-23.
- Marsden, Brian G. (June 8, 1988). "Satellites of Saturn and Uranus" (naming the moon). IAU Circular 4609. http://www.cbat.eps.harvard.edu/iauc/04600/04609.html. Retrieved 2011-12-23.
- Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission". Icarus 208 (1): 395–401. Bibcode 2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025. http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf.
- Verbiscer, A.; French, R.; Showalter, M.; Helfenstein, P. (9 February 2007). "Enceladus: Cosmic Graffiti Artist Caught in the Act". Science 315 (5813): 815. doi:10.1126/science.1134681. PMID 17289992. http://www.sciencemag.org/content/315/5813/815.abstract. Retrieved 20 December 2011. (supporting online material, table S1)
[edit] External links
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Wikimedia Commons has media related to: Helene |
- Helene Profile by NASA's Solar System Exploration
- The Planetary Society: Helene
- Helene has two faces – The Planetary Society : Helene Mini Atlas – Mar. 11, 2010
- Cassini catches Helene – The Planetary Society : Video & Views – Jun. 20, 2011
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