Emily LakdawallaMay 21, 2007

Many Cassini views of Tethys

Most of the time, when you see a montage of images of solar system bodies, the montage is depicting numerous different worlds. For the montage below, though, what you're looking at is fifteen different Cassini views of the same world, a cratered ball of ice called Tethys. At just over 1,000 kilometers in diameter, Tethys is Saturn's fifth largest moon.

Many Cassini views of Tethys
Many Cassini views of Tethys This montage presents just a few of the views of Tethys, Saturn's fifth largest moon, that have been captured by Cassini since its arrival. One prominent feature on Tethys is gigantic double-ringed impact basin called Odysseus; it is brought into relief in the second and third images in the second row of this montage. Tethys also has a backwards-"S"-shaped canyon system called Ithaca Chasma that curves around half of the moon. Another recognizable feature is a "T" shape made by five craters. These are clearest in the lower left image. Three craters make a vertical line: Phemius, Polyphemus, and Ajax. To the west of Polyphemus are two more: Arete and an unnamed crater. To the east of this "T" is a larger flat-floored crater, Penelope. Some of these images are public releases from the Cassini imaging team, while others have been composed from raw images by enthusiasts Gordan Ugarkovic and Orion.Image: NASA / JPL-Caltech / SSI / Gordan Ugarkovic / Orion

With all those craters, evidence suggests that not much has happened on Tethys for billions of years. But that curvy canyon of Ithaca Chasma, which can be seen to cross several of the global views above, hints that something interesting happened to the moon deep in its history, some geologic convulsion. On large worlds, like Earth and Venus, geologic activity produces lots of mountain belts all over the planet, which may have formed at different times and under different conditions. But on small worlds, like Tethys and Enceladus, geologic forces seem to have produced one gigantic feature that dominates the little world: Ithaca Chasma for Tethys, the hot geysers of the south polar terrain for Enceladus. It makes me wonder what kind of world Dawn is going to find at Ceres, which is just slightly smaller than Tethys.

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