Rhea

Discovery
Discovered by	Giovanni Domenico Cassini
Discovered in	December 23, 1672
Orbital characteristics [1]
Semimajor axis	527,108 km
Eccentricity	0.0012583
Revolution period	4.518212 d
Inclination	0.345° (to Saturn's equator)
Is a satellite of	Saturn
Physical characteristics
Mean diameter	1528 km
Surface area	7,300,000 km2
Mass	2.3166×1021 kg
Mean density	1.24 g/cm3
Surface gravity	0.26 m/s2
Rotation period	4.518212 d (synchronous)
Axial tilt	zero
Albedo	0.65
Surface temp.	min mean max 53 K 99 K
Atmosphere	none

Rhea (ree'-a, Greek ‘Ρέα) is the second largest moon of Saturn and was discovered in 1672 by Giovanni Domenico Cassini. Illustration for Rhea (moon) NASA image from Voyager 1 montage at http://grin. ... Giovanni Domenico (Jean-Dominique) Cassini Giovanni Domenico Cassini (June 8, 1625 - September 14, 1712) was an Italian-French astronomer and engineer. ... December 23 is the 357th day of the year in the Gregorian Calendar (358th in leap years). ... Events England, France, Munster and Cologne invade the United Provinces, therefore this name is know as ´het rampjaar´ (the disaster year) in the Netherlands. ... 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. ... 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. ... This article explains the meaning of area as a physical quantity. ... Square kilometre (US spelling: Square kilometer), symbol km², is an SI unit of surface area. ... 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: ρ - 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. ... 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. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ... 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. ... Events England, France, Munster and Cologne invade the United Provinces, therefore this name is know as ´het rampjaar´ (the disaster year) in the Netherlands. ... Giovanni Domenico (Jean-Dominique) Cassini Giovanni Domenico Cassini (June 8, 1625 - September 14, 1712) was an Italian-French astronomer and engineer. ...

Name

Rhea is named after the titan Rhea of Greek mythology. It is also designated Saturn V. In Greek mythology, the Titans (Greek Τιτάν, plural Τιτᾶνες) are among a series of gods, some of whom opposed Zeus and the Olympian gods in their ascent to power. ... Rhea (she who flows) was the Titaness daughter of Uranus and of Gaia. ... Greek mythology comprises the collected narratives of Greek gods, goddesses, heroes, and heroines, originally created and spread within an oral-poetic tradition. ...

Cassini named the four moons he discovered (Tethys, Dione, Rhea and Iapetus) Lodicea Sidera ("the stars of Louis") to honour king Louis XIV. Astronomers fell into the habit of referring to them and Titan as Saturn I through Saturn V. Once Mimas and Enceladus were discovered, in 1789, the numbering scheme was extended to Saturn VII. Atmosphere none Tethys (tee-this or teth-is, Greek Τηθύς) is a moon of Saturn that was discovered by Giovanni Domenico Cassini in 1684. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ... Iapetus (eye-ap-i-tus, Greek Ιαπετός) (British spelling: Japetus) is the third-largest moon of Saturn (see: Saturns natural satellites), discovered by Giovanni Domenico Cassini in 1671. ... Louis XIV King of France and Navarre By Hyacinthe Rigaud (1701) Louis XIV (Louis-Dieudonné) (September 5, 1638–September 1, 1715) reigned as King of France and King of Navarre from May 14, 1643 until his death. ... Titan (tye-tun, Greek Τιτάνας) is the largest moon of Saturn and the second largest moon in the solar system[1], after Jupiters moon Ganymede. ... Mimas (mye-mus) is a moon of Saturn that was discovered in 1789 by William Herschel. ... [4]; [5] Atmospheric characteristics Pressure trace, signficant spatial variability [6] Water Vapor 65% [7] Hydrogen 20% [8] Other CO2, CO, N2 [9] Enceladus (en-sel-a-dus, Greek Εγκέλαδος) is a moon of Saturn discovered in 1789 by William Herschel. ... 1789 was a common year starting on Thursday (see link for calendar). ...

The names of all seven satellites of Saturn then known come from John Herschel (son of William Herschel, discoverer of Mimas and Enceladus) in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope ([2]), wherein he suggested the names of the Titans, sisters and brothers of Cronos (the Greek Saturn), be used. John Herschel John Frederick William Herschel (7 March 1792 – 11 May 1871) was an English mathematician and astronomer. ... Sir Wilhelm Friedrich Herschel (Hanover, November 15, 1738 – August 25, 1822 Slough, then in Buckinghamshire now in Berkshire) was a German-born British astronomer and composer who became famous for discovering the planet Uranus, and made many other astronomical discoveries. ... 1847 was a common year starting on Friday (see link for calendar). ... This page is a candidate for speedy deletion, because: it is patent nonsense. ...

Physical characteristics

Cassini color image of Rhea, showing the wispy trailing hemisphere

Rhea is an icy body with a density of about 1,240 kg/m³. This low density indicates that it has a rocky core taking up less than one-third of the moon's mass with the rest composed of water-ice. Rhean features resemble those of Dione, with dissimilar leading and trailing hemispheres, suggesting similar composition and histories. The temperature on Rhea is 99 K (−174°C) in direct sunlight and between 73 K (−200°C) and 53 K (−220°C) in the shade. Image File history File links Download high resolution version (604x602, 23 KB)Cassini color image of Rhea taken Jan. ... Image File history File links Download high resolution version (604x602, 23 KB)Cassini color image of Rhea taken Jan. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ...

Rhea is heavily cratered and has bright wispy markings on its surface. Its surface can be divided into two geologically different areas based on crater density; the first area contains craters which are larger than 40 km in diameter, whereas the second area, in parts of the polar and equatorial regions, has craters under that size. This suggests that a major resurfacing event occurred some time during its formation. This article is about impact craters, also known as meteor craters. ...

The leading hemisphere is heavily cratered and uniformly bright. As on Callisto, the craters lack the high relief features seen on the Moon and Mercury. On the trailing hemisphere there is a network of bright swaths on a dark background and few visible craters. It is thought that these bright swaths may be material ejected from ice volcanoes early in Rhea's history when it was still liquid inside. However, recent observations of Dione, which has the same bright streaks, shows that these are in fact ice cliffs, and although close-up pictures of Rhea have not yet been taken by the Cassini probe, it is plausible to assume that the bright streaks on the Rhean surface are also ice cliffs. Atmospheric characteristics Atmospheric pressure trace Carbon dioxide 100% Callisto (ka-lis-toe, Greek Καλλιστώ) is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... For additional meanings, see Mercury (disambiguation). ... A volcano is a geological landform (usually a mountain) where magma (rock of the Earths interior made molten or liquid by extremely high temperatures along with a reduction in pressure and/or the introduction of water or other volatiles) erupts through the surface of the planet. ... This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. ...

See also:

• List of geological features on Rhea
• The asteroid 577 Rhea

The Cassini orbiter is due to perform a flyby of Rhea on November 25, 2005. This is a list of named geological features on Rhea. ... An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... November 25 is the 329th (in leap years the 330th) day of the year in the Gregorian calendar. ... 2005 is a common year starting on Saturday of the Gregorian calendar and is the current year. ...

External links

• The Planetary Society: Rhea

Atmosphere none Polydeuces (pol-ee-dew-seez, Greek Πολυδεύκης) is a natural satellite of Saturn that was discovered on images taken on October 21, 2004 by the Cassini imaging team, led by Carolyn C. Porco et al, and given the temporary designation S/2004 S 5. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ... Helene (hel-e-nee, Greek ‘Ελένη) is a moon of Saturn. ... Titan (tye-tun, Greek Τιτάνας) is the largest moon of Saturn and the second largest moon in the solar system[1], after Jupiters moon Ganymede. ...