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Rhea (moon)

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PIA07763 Rhea full globe5.jpg
Cassini view of Rhea's anti-Saturnian hemisphere, showing the moon's two largest impact basins (Mamaldi above and left of center, and adjacent Tirawa to its upper right). At highest resolution, several long linear features are visible: halfway down from center is Harahvaiti Fossa, while near the limb left of the bottom is Koykamou Catena.
Discovered by G. D. Cassini
Discovery time December 23, 1672
Other names Saturn V
Adjective Rhean
Longest distance from the center of its orbital path
("semi-major axis")
527 108 km
How egg-shaped its orbit is
0.001 258 3
How long it takes to complete an orbit 4.518 212 d
Angle above the reference plane
0.345° (to Saturn's equator)
What it orbits Saturn
Size and Other Qualities
Measures 1532.4×1525.6×1524.4 km 
Average distance from its center to its surface 763.8 ± 1.0 km 
Area of its surface 7 337 000 km²
Mass (2.306 518 ± 0.000 353)×1021 kg (~3.9×10−4 Earths)
Average density 1.236 ± 0.005 g/cm³
Gravity at its surface 0.265 m/s²
Slowest speed able to escape into space
("escape velocity")
0.635 km/s
How long it takes to turn around one time 4.518 212 d
Angle at which it turns
(in relation to its orbit)
How much light it reflects 0.949 ± 0.003 (geometric) 
Surface temp. Min. Avg. Max.
Kelvin 53 K   99 K
Seeming brightness
("apparent magnitude")
10 [2]
Photo of Rhea taken by the Cassini-Huygens probe

Rhea (/ˈrə/;[a] Ancient Greek: Ῥέᾱ) is Saturn's second largest moon. It is made of ice and rock.

Ring system

Rhea may have a thin ring system with three narrow bands in a disk of solid particles. These would be the first rings seen around a moon. The discovery was announced in the journal Science on March 6, 2008.


  1. In US dictionary transcription, US dict: rē′·ə.


  1. Natural Satellites Ephemeris Service Minor Planet Center
  2. Observatorio ARVAL (April 15, 2007). "Classic Satellites of the Solar System". Observatorio ARVAL. Retrieved 2011-12-17.