Aegaeon /iːˈdʒiːɒn/, or Saturn LIII (provisional designation S/2008 S 1), is a natural satelliteofSaturn. 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.
Aegaeon's crescent imaged by the Cassini spacecraft from a distance of 15238.2 km in 2010
| |
| Discovery | |
|---|---|
| Discovered by | Carolyn Porco |
| Discovery date | March 3, 2009 (2009-03-03) |
| Cassini Imaging Science Team | |
| Designations | |
Designation | Saturn LIII |
| Pronunciation | /iːˈdʒiːɒn/[1] |
Named after | Αιγαίων Aigaiōn |
| Adjectives | Aegaeonian /iːdʒiːˈoʊniən/[2] |
| Orbital characteristics | |
| Epoch JD 2454467.00075444 TDB | |
| 167493.665±0.004 km[3] | |
| Eccentricity | 0.00042277±0.00000004[3] |
| 0.80812 d[4] | |
| Inclination | 0.0007°±0.6°[3] |
| Satellite of | Saturn |
| Group | Source of the G Ring |
| Physical characteristics | |
| Dimensions | 1.40 × 0.50 × 0.40 km (± 0.10 × 0.12 × 0.16 km)[5]: 2 |
| 0.66±0.12 km[5]: 2 | |
| Volume | 0.15 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 |
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]
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]
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]
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.
