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 colloquially referred to as moons, a deriv ...

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 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

. It has an extremely elongated shape whose surface is thought to be similarly smooth as Methone. It orbits between

Janus In ancient Roman religion and myth, Janus ( ; ) 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 Janus (''Ianu ...

and Mimas within Saturn's G Ring.

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 scie ...

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

hekatonkheires In Greek mythology, the Hecatoncheires (), also called Hundred-Handers or Centimanes (; ), were three monstrous giants, of enormous size and strength, each with fifty heads and one hundred arms. They were individually named Cottus (the furious), ...

on 5 May 2009.

Orbit

Aegaeon orbits within the bright segment of Saturn's G Ring, 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 In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the longe ...

, 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 ang ...

. 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 reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

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 an extremely elongated shape, measuring in size. 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.

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.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 capture any images from a planned close flyby.

Notes

References

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