Aegaeon , or (provisional designation ), is a

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. It is thought to be similarly smooth as Methone. It orbits between

Janus In ancient Roman religion and myth, Janus ( ; la, Ianvs ) is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces. The month of January is named for Janu ...

and Mimas within Saturn's

G Ring G Ring may refer to: * Rings of Saturn#G Ring, a planetary ring system around Saturn. * G-ring In commutative algebra, a G-ring or Grothendieck ring is a Noetherian ring such that the map of any of its local rings to the completion is regular ( ...

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 Carolyn C. Porco (born March 6, 1953) is an American planetary scientist who explores the outer Solar System, beginning with her imaging work on the Voyager missions to Jupiter, Saturn, Uranus and Neptune in the 1980s. She led the imaging scienc ...

of the Cassini Imaging Science Team using the provisional designation . Aegaeon was named after one of the

hekatonkheires In Greek mythology, the Hecatoncheires ( grc-gre, Ἑκατόγχειρες, , Hundred-Handed Ones), or Hundred-Handers, also called the Centimanes, (; la, Centimani), named Cottus, Briareus (or Aegaeon (mythology), Aegaeon) and Gyges (or Gyes), ...

on 5 May 2009.

Orbit

Aegaeon orbits within the bright segment of Saturn's

, and is probably a major source of the ring.Petite Moon
, CICLOPS, 29 May 2009 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, 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 Mean longitude is the ecliptic longitude at which an orbiting body could be found if its orbit were circular and free of perturbations. While nominally a simple longitude, in practice the mean longitude does not correspond to any one physical angle ...

. It orbits Saturn at an average distance of 167,500 km in 0.80812 days, at an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of 0.001° to Saturn's equator, with an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.0002.

Physical characteristics

Aegaeon is the smallest known moon of Saturn outside of the rings and has a highly elongated shape, measuring in size. 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. 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.

Exploration

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.Planetary Society Cassini Timeline
/ref> An encounter on 27 January 2010 at a distance 13,306 km allowed ''Cassini'' to acquire its highest resolution images of Aegaeon. On 19 December 2015, ''Cassini'' was unable to acquire any images from a planned close flyby.

References

{{DEFAULTSORT:Aegaeon Moons of Saturn 20090303 Moons with a prograde orbit