Pallene (moon)
 Discovery image of Pallene | |
|---|---|
| Discovery | |
| Discovered by | Cassini Imaging Science Team |
| Discovered on | June 1, 2004 |
| Orbital characteristics[1] | |
| Semimajor axis | 212,280 ± 5 km |
| Eccentricity | 0.0040 |
| Orbital period | 1.153745829 d |
| Inclination (to Saturn's equator) |
0.1810 ± 0.0014° |
| Is a satellite of | Saturn |
| Physical characteristics | |
| Mean diameter | ≈ 4 km |
| Mass | 1.7 − 7 ×1013 kg [2] |
| Mean density | unknown |
| Surface gravity | unknown |
| Rotation period | synchronous |
| Axial tilt | unknown |
| Albedo | unknown |
| Atmosphere | none |
Pallene (Template:PronEng pə-LEE-nee, or as Greek Παλλήνη) is a very small natural satellite of Saturn lying between the orbits of Mimas and Enceladus.
It was first seen during the Cassini-Huygens mission by the Cassini Imaging Team[3][4] in 2004, and given the temporary designation S/2004 S 2. It was actually first seen on August 23, 1981 by Voyager 2 in a single photograph and named S/1981 S 14 and its distance to Saturn was then estimated at 200,000 km.[5] Since it was not visible in other images, its orbit could not be calculated at the time, but recent comparisons have identified it as matching Pallene's orbit.[1] Pallene is also designated as Saturn XXXIII.
Pallene is visibly affected by a perturbing mean longitude resonance with the much larger Enceladus, although this effect is not as large as the Mimas perturbations on Methone. The perturbations cause Pallene's osculating orbital elements to vary with an amplitude of about 4 km in semi-major axis, and 0.02° in longitude (corresponding to about 75 km). Eccentricity also changes on various timescales between 0.002 and 0.006, and inclination between about 0.178° and 0.184°.[1]
The names Methone and Pallene were provisionally approved by the IAU Division III Working Group for Planetary System Nomenclature in 2005[6] and were ratified at the IAU General Assembly in 2006. Pallene was one of the Alkyonides, the seven beautiful daughters of the Giant Alkyoneus.
The Pallene Ring, a faint dust ring, also discovered by the Cassini Imaging Team,[7] shares Pallene's orbit, as revealed by images taken in forward-scattered light by the Cassini spacecraft in 2006.[8] The ring has a radial extent of about 2,500 km. Its source is particles blasted off Pallene's surface by meteoroid impacts, which then form a diffuse ring around its orbital path.[9][10]
References
- ^ a b c Spitale, J. N.; et al. (2006). [Methone "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations"]. The Astronomical Journal. 132 (2): 692–710. doi:10.1086/505206.
{{cite journal}}: Check|url=value (help); Explicit use of et al. in:|author=(help) - ^ based on density 0.5 - 2 g/cm³
- ^ * C.C. Porco, et al., IAUC 8389: S/2004 S 1 and S/2004 S 2 August 16, 2004 (discovery)
- ^ Porco, C. C.; et al.; (2005); Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites, Science, Vol. 307, No. 5713, pp. 1226-1236
- ^ IAUC 6162: Possible Satellites of Saturn April 14, 1995
- ^ IAUC 8471: Satellites of Saturn January 21, 2005 (naming the moon)
- ^ C.C. Porco, et al., IAUC 8759: Rings of Saturn (R/2006 S 1, R/2006 S 2, R/2006 S 3, R/2006 S 4) (subscription-only) October 11, 2006
- ^ Moonmade Rings
- ^ Cassini-Huygens press release NASA Finds Saturn's Moons May Be Creating New Rings, October 11, 2006
- ^ Early press releases of the discovery mentioned the first person to see the moon in Cassini images. This bit of trivia was blown out of proportion in the following months, with this individual being credited as the "discoverer" by some sources. Because the discovery was a large team effort, involving tens of people and hundreds of hours of distributed work, a conscious decision was made by the IAU to officially and correctly assign any credit to "the Cassini Imaging team" and to avoid unfairly singling out any one individual as the discoverer.
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