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[3]
Epoch 2008 January 1.5 UTC
167494±4 km
Eccentricity0.00024±0.00023
0.80812 d[4]
Inclination0.0010°±0.0009°
Satellite ofSaturn
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
synchronous[5]: 4 
assumed zero
Albedo~ 0.15[6]: 26 
0.25±0.23 (geometric)[7]: 1010 

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.[8] It orbits between Janus and Mimas within Saturn's G Ring, in a 7:6 orbital resonance with the latter. Compared to the similar moons Anthe and Methone, which are both in orbital resonances with Mimas, Aegaeon is more tightly trapped in its resonance than the other two.[3] In addition, all three of the moons are associated with arc structures formed from material blasted off their surfaces, but Aegaeon is the smallest among the three while its arc is the brightest.[3]

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.[9]

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.[10] 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 main 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.[7] Aegaeon is rounded into hydrostatic equillibrium likely due to a somewhat low density and a highly porous and icy interior structure.[5] Aegaeon is exceptionally dark with an albedo of roughly 0.15, comparable to the dark side of Iapetus.[6] 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.[11]

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.[12] An encounter on 27 January 2010 at a distance 13,306 km allowed Cassini to acquire its highest resolution images of Aegaeon.[11] 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 h 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. ^ a b Hedman, M. M.; Helfenstein, P.; Chancia, R. O.; Thomas, P.; Roussos, E.; Paranicas, C.; Verbiscer, A. J. (April 2020). "Photometric Analyses of Saturn's Small Moons: Aegaeon, Methone, and Pallene Are Dark; Helene and Calypso Are Bright". The Astronomical Journal. 159 (4): 48. arXiv:1912.09192. Bibcode:2020AJ....159..129H. doi:10.3847/1538-3881/ab659d. S2CID 209414585. 129.
  7. ^ a b 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. ^ Battersby, S. (2013-05-17). "Saturn's egg moon Methone is made of fluff". www.newscientist.com. New Scientist. Retrieved 2013-05-21.
  9. ^ Jennifer Blue, Saturnian Satellite Named Aegaeon, USGS Astrogeology Hot Topics, 5 May 2009
  10. ^ Petite Moon Archived 2011-07-25 at the Wayback Machine, CICLOPS, 29 May 2009
  11. ^ a b 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.
  12. ^ "Planetary Society Cassini Timeline". The Planetary Society.{{cite web}}: CS1 maint: url-status (link)
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