Credit: NASA/JPL/Space Science Institute

NASA recently published a beautiful image of Saturn’s graceful rings and two of the planet’s bizarre icy moons. The image was acquired by the Saturn-orbiting Cassini spacecraft. The moons in the image are Rhea (1,528 km across), visible at lower right, and tiny Telesto (25 km across), which shines as a bright speck, below center. The rings are visible as thin lines, in the top of image.

Cassini was looking on the dark side of the rings, from just below the plane of the rings. The image was taken in visible light with Cassini’s narrow-angle camera, on 5 September 2010. The spacecraft was at a distance of approximately 1.6 million km from Telesto. Rhea was 1.9 million km from Cassini.

Rhea, Saturn’s second largest moon, orbits Saturn every 4.5 days, at a distance of approximately 530,000 km. For comparison, the Moon orbits earth every 27.3 days, at a an average distance of approximately 384,000 km. Rhea is heavily cratered. Its low mean density is only slightly greater than that of water, indicating that Rhea is composed largely of water ice, with only about 25% of rock. In Greek mythology, Rhea was a sister of Cronus (Saturn), the god of agriculture, and a daughter of Uranus, the god of heaven, and Gaia, the goddess of Earth.

Telesto orbits Saturn every 1.88 days, at a distance of approximately 295,000 km. It is a rugged, irregularly-shaped satellite. In Greek mythology, Telesto was a daughter of Oceanus, the world-ocean. 

References

NASA’s Photojournal

Wikipedia

Further Reading

The Cassini Mission Homepage

http://saturn.jpl.nasa.gov/

Aymen Mohamed Ibrahem
Senior Astronomy Specialist