Credit: NASA/JPL/Space Science Institute

NASA recently published a spectacular image of Tethys, Saturn's intriguing icy moon. The image was acquired by the Saturn-bound Cassini spacecraft. It shows a magnificent surface feature on Tethys, a gigantic impact crater.

The crater, known as Odysseus, is about 450 km across, nearly 2/5 the diameter of Tethys (1,071 km across). Odysseus is classified as an ancient, multi-ringed impact basin. The outer ring is defined by steep, cliff-like walls that descend to generally broad internal terraces. The inner ring is formed by a prominent, crown-shaped, 140-km diameter circular band of icy mountains. Interestingly, multi-ring basins are seen on rocky objects as well as icy ones.

The complex internal structure and multi-ringed nature of these very large basins are believed to arise from the rebound of intense shock waves that formed at the time of impact. Scientists believe that the surface of Tethys may have been fluid during the time of the impact which could have shattered the moon.

Four clear-filter, narrow-angle images were combined to create this mosaic. North is up. The resolution is 572 m per pixel.

The view was obtained by the Cassini spacecraft on 30 August 2007, from a distance of approximately 97,000 km from Tethys.

Tethys has another amazing surface feature, a huge valley, known as Ithaca Chasma. This valley, 100 km wide and 3-5 km deep, extends 2000 km or 3/4 of Tethys' circumference.

Tethys' mean density is slightly less than that of water. This low density indicates that Tethys is primarily composed of water ice. Tethys orbits Saturn every 1.9 days, at a distance of approximately 300,000 km. Telesto (approximately 30 km across) and Calypso (approximately 26 km across) share Tethys its orbit around Saturn.

In Greek mythology, Tethys was a sea goddess and the wife of Oceanus, the personification of the world-ocean.

Further Reading

Cassini-Huygens Mission to Saturn

http://saturn.jpl.nasa.gov/home/index.cfm

The Eight Planets

www.nineplanets.org/

Aymen Mohamed Ibrahem

Senior Astronomy Specialist