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Pallene (moon)

(Redirected from S/2004 S2)

Pallene /pəˈliːniː/ is a very small natural satellite of Saturn. It is one of three small moons known as the Alkyonides that lie between the orbits of the larger Mimas and Enceladus. It is also designated Saturn XXXIII.

Pallene
Cassini image of Pallene transiting Saturn on October 16, 2010
Discovery
Discovered byVoyager 2 (first discovery)
Cassini Imaging Team[1]
Discovery dateJune 1, 2004 (second discovery by Cassini-Huygens)
Designations
Designation
Saturn XXXIII
Pronunciation/pəˈliːniː/[2]
Named after
Παλλήνη Pallēnē
S/1981 S 14 (first discovery)
S/2004 S 2 (second discovery)
AdjectivesPallenean /pæləˈniːən/[3]
Orbital characteristics[4]
Epoch 20 June 2004 (JD 2453177.5)
212300 km[5]
Eccentricity0.004[5]
1.009549 d[5]
Inclination0.1810°±0.0014° (to Saturn's equator)
Satellite ofSaturn
GroupAlkyonides
Physical characteristics
Dimensions5.76 × 4.16 × 3.68 km
(± 0.14 × 0.14 × 0.14 km)[6]: 2 
4.46±0.14 km[6]: 2 
Volume46.5 km3[a]
Mass(1.15±0.40)×1013 kg[6]: 3 
Mean density
0.251±0.075 g/cm3[6]: 3 
0.011–0.016 mm/s2[6]: 3 
0.0007 km/s at longest axis
to 0.0009 km/s at poles
synchronous
zero

Discovery

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Discovery image of Pallene in 2004 from the Cassini probe

Pallene was discovered by the Cassini Imaging Team in 2004, during the Cassini–Huygens mission.[7][8] It was given the temporary designation S/2004 S 2. In 2005, the name Pallene was provisionally approved by the IAU Division III Working Group for Planetary System Nomenclature,[9] and was ratified at the IAU General Assembly in 2006. The name refers to Pallene, one of the Alkyonides, the seven beautiful daughters of the giant Alkyoneus.

After the discovery in 2004, it was realized that Pallene had been first photographed on August 23, 1981, by the space probe Voyager 2. It had appeared in a single photograph and had been provisionally named S/1981 S 14 and estimated to orbit 200,000 km from Saturn.[10] Because it had not been visible in other images, it had not been possible to compute its orbit at the time, but recent comparisons have shown it to match Pallene's orbit.[4]

Orbital characteristics

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Pallene is visibly affected by a perturbing mean-longitude resonance with the much larger Enceladus, although this effect is not as large as Mimas's 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°.[4]

Ring

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Back-illuminated rings of Saturn as seen by Cassini on 15 September 2006. The faint Pallene ring is visible at the bottom left as indicated.

In 2006, images taken in forward-scattered light by the Cassini spacecraft enabled the Cassini Imaging Team to discover a faint dust ring around Saturn that shares Pallene's orbit, now named the Pallene Ring.[11][12] 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.[13][14]

Exploration

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Pallene's crescent illuminated by Saturnshine, imaged by Cassini on 14 September 2011

The Cassini spacecraft, which studied Saturn and its moons until September, 2017, performed a fly-by of Pallene on 16 October 2010, and 14 September 2011 at a distance of 36,000 kilometers (22,000 miles) and 44,000 kilometers respectively.[15]

Notes

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  1. ^ Calculated from Pallene's volume-equivalent sphere radius of 2.23±0.07 km given by Thomas et al. (2020)[6]: 2 

References

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Citations

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  1. ^ Cassini Imaging Team.
  2. ^ Noah Webster (1884) A Practical Dictionary of the English Language
  3. ^ "JPL (ca. 2008) Cassini Equinox Mission: Pallene". Archived from the original on 2016-04-12. Retrieved 2020-03-05.
  4. ^ a b c Spitale Jacobson et al. 2006.
  5. ^ a b c "Planetary Satellite Mean Orbital Parameters". Jet Propulsion Laboratory. Retrieved 5 June 2023.
  6. ^ a b c d e f Thomas & Helfenstein 2020.
  7. ^ IAUC 8389.
  8. ^ Porco Baker et al. 2005.
  9. ^ IAUC 8471.
  10. ^ IAUC 6162.
  11. ^ IAUC 8759.
  12. ^ CICLOPS 2006, Moonmade Rings.
  13. ^ JPL/NASA: Creating New Rings.
  14. ^ Hedman et al., 2009.
  15. ^ "Cassini Tour Event Summary – Planned Observations of Small Satellites". Planetary Atmospheres Node. Planetary Data Services. Retrieved 31 March 2022.

Sources

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