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Epimetheus (ep'-i-mee'-thee-us, Greek Επιμηθεύς) is a moon of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus. Image File history File links Epimetheus, a moon of Saturn, photographed by the Cassini orbiter, 2005 File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
December 18 is the 352nd day of the year (353rd in leap years) in the Gregorian Calendar. ...
1966 was a common year starting on Saturday (link goes to calendar) // Events January January 1 - In a coup, Colonel Jean-Bédel Bokassa ousts president David Dacko and takes over the Central African Republic. ...
In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...
In geometry, the semi-major axis (also semimajor axis) a applies to ellipses and hyperbolas. ...
A kilometre (American spelling: kilometer) (symbol: km) is a unit of length equal to 1000 metres (from the Greek words khilia = thousand and metro = count/measure). ...
In astrodynamics, under standard assumptions any orbit must be of conic section shape. ...
The orbital period is the time it takes a planet (or another object) to make one full orbit. ...
Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ...
Moons of solar system scaled to Earths Moon The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. ...
Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ...
For the geometric term, see diameter. ...
Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ...
The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ...
Density (symbol: Ï - Greek: rho) is a measure of mass per unit of volume. ...
It has been suggested that Law of universal gravitation be merged into this article or section. ...
Acceleration is the time rate of change of velocity, and at any point on a v-t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ...
On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ...
In astronomy, synchronous rotation is a planetological term describing a body orbiting another, where the orbiting body takes as long to rotate on its axis as it does to make one orbit; and therefore always keeps the same hemisphere pointed at the body it is orbiting. ...
Axial tilt is an astronomical term regarding the inclination angle of a planets rotational axis in relation to its orbital plane. ...
The albedo is a measure of reflectivity of a surface or body. ...
Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ...
Moons of solar system scaled to Earths Moon The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. ...
Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ...
In Greek mythology, Epimetheus was the son of Iapetus and brother of Prometheus and Atlas; Epimetheus is Greek for hindsight. ...
There is also an asteroid called 1810 Epimetheus. An asteroid is a small, solid object in our Solar System, orbiting the Sun. ...
1810 Epimetheus is an asteroid that was discovered on September 24, 1960 by Cornelis Johannes Van Houten and Ingrid Van Houten-Groeneveld at Palomar Observatory near Pauma Valley, California. ...
Discovery
Epimetheus occupies essentially the same orbit as the moon Janus. Astronomers assumed that there was only one body in that orbit, and accordingly had a hard time figuring out their orbital characteristics; it is obviously impossible to reconcile the observations of two distinct objects as a single object. Janus (jay-nus, Greek Ιανός) is a moon of Saturn. ...
Audouin Dollfus observed a moon on December 15, 1966, which he proposed to be named "Janus"[3]. On December 18, Richard L. Walker made a similar observation which is now credited as the discovery of Epimetheus[4]. However, at the time, it was believed that there was only one moon, unofficially known as "Janus", in the given orbit. Audouin Charles Dollfus (November 12, 1924 – ) is a French astronomer. ...
December 15 is the 349th day of the year (350th in leap years) in the Gregorian calendar. ...
1966 was a common year starting on Saturday (link goes to calendar) // Events January January 1 - In a coup, Colonel Jean-Bédel Bokassa ousts president David Dacko and takes over the Central African Republic. ...
December 18 is the 352nd day of the year (353rd in leap years) in the Gregorian Calendar. ...
Twelve years later, in October 1978, Stephen M. Larson and John W. Fountain realised that the 1966 observations were best explained by two distinct objects (Janus and Epimetheus) sharing very similar orbits. This was confirmed in 1980 by Voyager 1, and so Walker officially shares the discovery of Epimetheus with Larson and Fountain. 1978 was a common year starting on Sunday (the link is to a full 1978 calendar). ...
1980 is a leap year starting on Tuesday. ...
A NASA artists rendition of a Voyager spacecraft The Voyager 1 spacecraft is an 815-kilogram unmanned probe of the outer solar system and beyond, launched September 5, 1977, and currently operational. ...
The 1980 Voyager discovery was designated S/1980 S 3, and it was officially named "Epimetheus" in 1983. The name Janus was officially approved by the IAU at the same time, although the name had been used informally since Dollfus proposed it a few days after the 1966 discovery. 1980 is a leap year starting on Tuesday. ...
1983 is a common year starting on Saturday of the Gregorian calendar. ...
Logo of the IAU The International Astronomical Union (IAU) unites national astronomical societies from around the world. ...
Orbital relationship between Epimetheus and Janus Epimetheus and Janus are "co-orbital". Janus' orbital radius from Saturn is 151,472 km and Epimetheus' orbital radius is 151,422 km, a separation of only 50 km. Since closer orbits have higher velocities the two moons must inevitably approach each other, and since Epimetheus' diameter is 115 km and Janus' is 178 km it would seem at first glance that a collision is also inevitable. But as the inner moon catches up with the outer moon their mutual gravitational attraction boosts the inner moon's momentum and raises its orbit, causing it to slow down. The outer moon loses an equal amount of momentum and drops into a lower orbit at the same time, speeding it up. The moons thus "trade" orbits and begin moving apart again, without actually approaching each other closely. The exchange takes place about once every four years; the next closest approach is in Jan/Feb 2006. This arrangement is unique in the solar system, as far as is currently known. Janus (jay-nus, Greek Ιανός) is a moon of Saturn. ...
In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...
2005 is a common year starting on Saturday of the Gregorian calendar. ...
Presentation of the solar system (not to scale). ...
Other unusual orbits include the retrograde orbit of Triton around Neptune, and the "horse-shoe" orbit of Cruithne and (potentially) dozens of other objects in similar orbits [5]. Triton (trye-tun, Greek ΤÏίτων) is the planet Neptunes largest moon, discovered by William Lassell on 1846-10-10, just 17 days after the planet itself was discovered. ...
Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ...
See: the asteroid 3753 Cruithne said (incorrectly) by some to be a moon Cruithne, the ancient Brythonic tribe sometimes identified with the Picts This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...
Physical characteristics
 Epimetheus, as imaged by Voyager 1 (NASA) There are several Epimethean craters larger than 30 km in diameter, as well as both large and small ridges and grooves. The extensive cratering indicates that Epimetheus must be quite old. Janus and Epimetheus may have formed from a disruption of a single parent to form co-orbital satellites, but if this is the case the disruption must have happened early in the history of the satellite system. From its very low density and relatively high albedo, it seems likely that Epimetheus is a very porous icy body. There is a lot of uncertainty in these values, however, and so this remains to be confirmed. Epimetheus, Saturns moon. ...
Epimetheus, Saturns moon. ...
The albedo is a measure of reflectivity of a surface or body. ...
The Cassini orbiter is due to perform a flyby of Epimetheus on December 3, 2007. This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. ...
December 3 is the 337th (in leap years the 338th) day of the year in the Gregorian calendar. ...
2007 is a common year starting on Monday of the Gregorian calendar. ...
See also This is list of named geological features on Janus, Epimetheus and Phoebe. ...
External links - The Planetary Society: Epimetheus
Pandora (pan-dor-a, Greek ΠανδώÏα) is a moon of Saturn. ...
Janus (jay-nus, Greek Ιανός) is a moon of Saturn. ...
Mimas (mye-mus, Greek Μίμας, Μῑμάντ-) is a moon of Saturn that was discovered in 1789 by William Herschel. ...
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