|ESA Science & Technology||04-Jul-2005 14:22:59|
Knowledge before Cassini-Huygens
Thethys is a heavily cratered moon - including the 400 km diameter Odysseus crater. This crater is of some interest as the floor appears to be relatively shallow, suggesting some kind of flow process (possibly ice) has occurred to partially fill the crater since its formation.
The other major feature on the moon's surface is Ithaca Chasma, a 2000 km long valley that spans upto three-quarters of the surface of the planet. It is typically 100 km wide and a few kilometres deep. There are currently two competing ideas for its formation: it formed as a surface fracture as a result of the impact which formed Odysseus; or it formed when liquid water expanded in the core as it froze.
Tethys also has two companions in its orbit - Telesto and Calypso. These are small moons, roughly 20 km in diameter, that orbit at Lagrange points 60 ° ahead and behind the position of Tethys. [Note: these orbital positions are highly stable and are the same orbital points that the Trojan asteroids occupy around Jupiter's orbit]
*Note: in the following section all images courtesy NASA/JPL/Space Science Institute unless stated otherwise.
21 July 2004Cassini Instrument: Imaging Science Subsystem
3 August 2004Cassini Instrument: Imaging Science Subsystem
11 November 2004Cassini Instrument: Imaging Science Subsystem
23 November 2004Cassini Instrument: Imaging Science Subsystem
Having passed closer to Tethys than the Voyager 2 spacecraft, Cassini has returned the best-ever natural colour view of this icy moon. As seen here, the battered surface of Tethys has a neutral hue. The image is a mosaic of two footprints.
The result reveals a world awash with craters - many small craters lie on top of older, larger ones, suggesting an ancient surface. At the top and along the boundary between day and night, the moon's terrain has a grooved appearance.
17 December 2004Cassini Instrument: Imaging Science Subsystem
This view of Tethys shows principally the Saturn-facing hemisphere of the moon. In the centre of the image part of the tremendous rift called Ithaca Chasma can be seen. It is 100 kilometres wide in places, and runs nearly three-quarters of the way around the icy moon. Adjacent to the great Chasma is a large multi-ring impact basin with a diameter of about 300 kilometres. The inner ring of the basin is about 130 kilometres in diameter.
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