Aegaeon (/ˈən/ ee-JEE-ən; or as Greek Αιγαίων), also Saturn LIII (provisional designation S/2008 S 1), is a natural satellite of Saturn. It is thought to be similarly smooth as Methone.[4] It orbits between Janus and Mimas within Saturn's G Ring.

N1643264379 1.jpg
Aegaeon imaged by the Cassini spacecraft from a distance of 15238.2 km in 2010
Discovered byCarolyn Porco
Discovery dateMarch 3, 2009 (2009-03-03)
Cassini Imaging Science Team
Orbital characteristics
Epoch JD 2454467.00075444 TDB
167493.665±0.004 km [1]
Eccentricity0.00042277±0.00000004 [1]
0.80812 d [2]
Inclination0.0007°±0.6° [1]
(linear drift) 445.475±0.007°/day
Physical characteristics
Dimensions1.4 km × 0.5 km × 0.4 km
± 0.1 km × 0.12 km × 0.16 km[3]
Mean radius
0.33±0.06 km[3]
Mean density
Albedo< 0.15

Discovery and namingEdit

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.[2]

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


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.[6] 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,[1] 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.[2]

Physical characteristicsEdit

Aegaeon is the smallest known moon of Saturn and has a highly elongated shape, measuring 1.4 km × 0.5 km × 0.4 km (0.87 mi × 0.31 mi × 0.25 mi) in size.[7] Measurements of its mass, based on its interaction with the dust particles that make up the G ring arc the moon is embedded in, suggest a density similar to that of water ice.[8] Aegaeon has the lowest albedo, below 0.15, of any Saturnian moon inward of Titan.[8] 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.[8]


The Cassini spacecraft has performed four flybys of Aegaeon closer than 20,000 km, though only one has occurred since it was discovered in 2008. The closest of these pre-discovery encounters took place on 5 September 2005 at a distance of 8,517 km.[9] An encounter on 27 January 2010 at a distance 13,306 km allowed Cassini to acquire its highest resolution images of Aegaeon to-date.[8] On 19 December 2015, Cassini was unable to acquire any images from a planned close flyby.


  1. ^ 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.
  2. ^ a b c IAU Circular No. 9023
  3. ^ a b c Thomas, P. C.; Burns, J. A.; Tiscareno, M. S.; Hedman, M. M.; et al. (2013). "Saturn's Mysterious Arc-Embedded Moons: Recycled Fluff?" (PDF). 44th Lunar and Planetary Science Conference. p. 1598. Retrieved 2013-05-21.
  4. ^ Battersby, S. (2013-05-17). "Saturn's egg moon Methone is made of fluff". New Scientist. Retrieved 2013-05-21.
  5. ^ Jennifer Blue, Saturnian Satellite Named Aegaeon, USGS Astrogeology Hot Topics, 5 May 2009
  6. ^ Petite Moon, CICLOPS, 29 May 2009
  7. ^ 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.
  8. ^ a b c d 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. 6. Retrieved 2 December 2015.
  9. ^ Planetary Society Cassini Timeline