| Aegaeon | |
| Pronounced: | [1] |
| Named After: | Αιγαίων Aigaiōn |
| Adjective: | Aegaeonian [2] |
| Mpc Name: | Saturn LIII |
| Discovery Method: | Cassini Imaging Science Team |
| Apsis: | astron |
| Discoverer: | Carolyn Porco |
| Semimajor: | [3] |
| Period: | 0.80812 d |
| Satellite Of: | Saturn |
| Group: | Source of the G Ring |
| Dimensions: | km (± km) |
| Surface Grav: | (0.9–1.3 micro-g) |
| Escape Velocity: | km/s at longest axis to km/s at poles |
| Rotation: | assumed synchronous |
| Epoch: | JD 2454467.00075444 TDB |
| Albedo: | < 0.15 |
Aegaeon, or (provisional designation ), is a natural satellite of Saturn. It has an extremely elongated shape whose surface is thought to be similarly smooth as Methone.[4] It orbits between Janus and Mimas within Saturn's G Ring.
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 .[5]
Aegaeon was named after one of the hekatonkheires on 5 May 2009.[6]
Aegaeon orbits within the bright segment of Saturn's G Ring, and is probably a major source of the ring.[7] 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.[5]
Aegaeon is the smallest known moon of Saturn outside of the rings and has an extremely elongated shape, measuring 1.4x in size.[8] Measurements of its mass show that Aegaeon has a very low density, likely due to a highly porous and icy interior structure. Aegaeon has the lowest albedo, below 0.15, of any Saturnian moon inward of Titan. 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.
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.[9] 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.