Helene (måne)
| Helene | |
|---|---|
 | |
| Opdaget | |
| 1. marts 1980, af Pierre Laques og Jean Lecacheux | |
| Kredsløb om Saturn | |
| Afstand til Saturn (massecenter) |
|
| Halve storakse | 377 396 km |
| Halve lilleakse | 377 395 km |
| Excentricitet | 0,0022 |
| Siderisk omløbstid | 2d 17t 41m 9,46s |
| Synodisk periode | — |
| Omløbshastighed |
|
| Banehældning | 0,199° i fh. t. Saturns ækv. |
| Periapsisargument; ω | — ° |
| Opstigende knudes længde; Ω | — ° |
| Omgivelser | |
| — | |
| Fysiske egenskaber | |
| Diameter | 30,0 – 36,0 km |
| Fladtrykthed | — |
| Overfladeareal | 3,2·103 km² |
| Rumfang | — km³ |
| Masse | 2,500·1015 kg |
| Massefylde | 1500 kg/m³ |
| Tyngdeacc. v. ovfl. | 0,006 7 m/s² |
| Undvigelseshastighed v. ækv. | 18 km/t |
| Rotationstid | 2d 17t 41m 9,46s (Bunden rotation) |
| Aksehældning | 0 |
| Nordpolens rektascension | — |
| Nordpolens deklination | — ° |
| Magnetfelt | — |
| Albedo | 60 % |
| Temperatur v. ovfl. | Gnsn. — °C Min. — °C Maks. — °C |
| Atmosfære | |
| Atmosfæretryk | 0 hPa |
| Atmosfærens sammensætning | — |
Helene er en af planeten Saturns måner: Den blev opdaget 1. marts 1980 af Pierre Laques og Jean Lecacheux, som observerede den fra Pic du Midi-observatoriet. Den kendes også som Saturn XII (XII er romertallet for 12), men lige efter opdagelsen fik den den midlertidige betegnelse S/1980 S 6. I 1988 vedtog den Internationale Astronomiske Union at opkalde den efter amazonen Helene fra den græske mytologi.
Helene følger samme omløbsbane omkring Saturn, på den måde at Helene ligger i Lagrange-punktet L4 i Saturn-Dione-systemet; hele tiden 60 grader foran Dione, og af den grund er Helene undertiden blevet omtalt som "Dione B". Månen Polydeuces befinder sig ved punktet L5 i samme system.
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This raw, unprocessed image of Saturn's moon Helene was taken by Cassini on 18. juni 2011 and received on Earth 20. juni 2011.
Helene is a trojan moon of Dione. It leads Dione by 60 degrees in their shared orbit. The view looks toward the leading hemisphere of Helene (33 kilometers, 21 miles across). North on Helene is towards the top.
The camera was pointing toward Helene, and the image was taken using the CL1 and CL2 filters. The image has not been validated or calibrated. A validated/calibrated image will be archived with the Planetary Data System in 2012.
The Cassini Solstice Mission is a joint United States and European endeavor. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colorado.
For more information about the Cassini Solstice Mission visit http://ciclops.org, http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
The original NASA image has been modified by cropping, sharpening and lightening shadows.