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Aegaeon (moon)

Aegaeon
Aegaeon's crescent imaged by the Cassini spacecraft from a distance of 15238.2 km in 2010
Discovery
Discovered byCarolyn Porco
Discovery dateMarch 3, 2009 (2009-03-03)
Cassini Imaging Science Team
Designations
Designation
Saturn LIII
Pronunciation/iːˈdʒiːɒn/[1]
Named after
Αιγαίων Aigaiōn
AdjectivesAegaeonian /iːdʒiːˈoʊniən/[2]
Orbital characteristics
Epoch JD 2454467.00075444 TDB
167493.665±0.004 km[3]
Eccentricity0.00042277±0.00000004[3]
0.80812 d[4]
Inclination0.0007°±0.6°[3]
Satellite ofSaturn
GroupSource of the G Ring
Physical characteristics
Dimensions1.40 × 0.50 × 0.40 km
(± 0.10 × 0.12 × 0.16 km)[5]: 2 
0.66±0.12 km[5]: 2 
Volume0.15 km3[a]
Mass(7.82±3.00)×1010 kg[5]: 3 
Mean density
0.539±0.140 g/cm3[5]: 3 
0.009–0.013 mm/s2[5]: 3 
(0.9–1.3 micro-g)
0.001 km/s at longest axis
to 0.002 km/s at poles
assumed synchronous
Albedo< 0.15

Aegaeon /iːˈdʒiːɒn/, or Saturn LIII (provisional designation S/2008 S 1), is a natural satellite of Saturn. It has an extremely elongated shape whose surface is thought to be similarly smooth as Methone.[6] It orbits between Janus and Mimas within Saturn's G Ring.

Discovery and naming

Images of Aegaeon were taken by Cassini on 15 August 2008, and its discovery was announced on 3 March 2009 by Carolyn Porco of the Cassini Imaging Science Team using the provisional designation S/2008 S 1.[4]

Aegaeon was named after one of the hekatonkheires on 5 May 2009.[7]

Orbit

2008 Cassini images of the bright G Ring arc with Aegaeon embedded within it. These images were taken over the course of ten minutes.

Aegaeon orbits within the bright segment of Saturn's G Ring, and is probably a major source of the ring.[8] Debris knocked off Aegaeon forms a bright arc near the inner edge, which in turn spreads to form the rest of the ring. Aegaeon orbits in a 7:6 corotation eccentricity resonance with Mimas,[3] which causes an approximately 4-year oscillation of about 4 km in its semi-major axis, and a corresponding oscillation of a few degrees in its mean longitude. It orbits Saturn at an average distance of 167,500 km in 0.80812 days, at an inclination of 0.001° to Saturn's equator, with an eccentricity of 0.0002.[4]

Physical characteristics

Aegaeon is the smallest known moon of Saturn outside of the rings and has an extremely elongated shape, measuring 1.4 km × 0.5 km × 0.4 km (0.87 mi × 0.31 mi × 0.25 mi) in size.[9] Measurements of its mass show that Aegaeon has a very low density, likely due to a highly porous and icy interior structure.[5] Aegaeon has the lowest albedo, below 0.15, of any Saturnian moon inward of Titan.[10] This might be due to either darker meteoric material making up the dust in the G ring or due to Aegaeon having been disrupted, stripping away its ice-rich surface and leaving the rocky inner core behind.[10]

Exploration

The Cassini spacecraft has performed four flybys of Aegaeon closer than 20,000 km, though only one has occurred since its discovery in 2008. The closest of these pre-discovery encounters took place on 5 September 2005 at a distance of 8,517 km.[11] An encounter on 27 January 2010 at a distance 13,306 km allowed Cassini to acquire its highest resolution images of Aegaeon.[10] On 19 December 2015, Cassini was unable to capture any images from a planned close flyby.

Notes

  1. ^ Calculated from Aegaeon's volume-equivalent sphere radius of 0.33±0.06 km given by Thomas et al. (2020)[5]: 2 

References

  1. ^ Noah Webster (1884) A Practical Dictionary of the English Language
  2. ^ Maravilla, D.; Leal-Herrera, J. L. (2014). "The Saturnian G-Ring: A Short Note about its Formation". Revista Mexicana de Astronomía y Astrofísica. 50 (2): 342, 346, 347. Bibcode:2014RMxAA..50..341M. ISSN 0185-1101.
  3. ^ a b c d Hedman, M.M.; Cooper, N.J.; Murray, C.D.; Beurle, K.; Evans, M.W.; Tiscareno, M.S.; Burns, J.A. (May 2010). "Aegaeon (Saturn LIII), a G-ring object". Icarus. 207 (1): 433–447. arXiv:0911.0171. Bibcode:2010Icar..207..433H. doi:10.1016/j.icarus.2009.10.024. S2CID 118559643.
  4. ^ a b c "IAU Circular No. 9023". Archived from the original on 2019-05-01. Retrieved 2009-03-04.
  5. ^ a b c d e f g Thomas, P. C.; Helfenstein, P. (July 2020). "The small inner satellites of Saturn: Shapes, structures and some implications". Icarus. 344: 20. Bibcode:2020Icar..34413355T. doi:10.1016/j.icarus.2019.06.016. S2CID 197474587. 113355.
  6. ^ Battersby, S. (2013-05-17). "Saturn's egg moon Methone is made of fluff". www.newscientist.com. New Scientist. Retrieved 2013-05-21.
  7. ^ Jennifer Blue, Saturnian Satellite Named Aegaeon, USGS Astrogeology Hot Topics, 5 May 2009
  8. ^ Petite Moon Archived 2011-07-25 at the Wayback Machine, CICLOPS, 29 May 2009
  9. ^ Thomas, P.C.; Burns, J.A.; Hedman, M.; Helfenstein, P.; Morrison, S.; Tiscareno, M.S.; Veverka, J. (2013). "The inner small satellites of Saturn: A variety of worlds" (PDF). Icarus. 226 (1): 999–1019. Bibcode:2013Icar..226..999T. doi:10.1016/j.icarus.2013.07.022. Retrieved 2 December 2015.
  10. ^ a b c Hedman, M.M.; Burns, J.A.; Thomas, P.C.; Tiscareno, M.S.; Evans, M.W. (2011). Physical Properties of the small moon Aegaeon (Saturn LIII) (PDF). European Planetary Space Conference. Icarus. Vol. 6. Archived from the original (PDF) on 4 March 2016. Retrieved 2 December 2015.
  11. ^ Planetary Society Cassini Timeline
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