Cassini imaged Tethys on May 27th from 166,000 miles. That’s two-thirds the distance between Earth and our moon. You can see Ithaca Chasma just to the right of center, running up and down from the space probe’s perspective. It may be hard to trust the factor of glare, but there’s a shiny appearance to this moon that strikes me as different from the images of nearby Rhea.
Tethys masses more than the geyser moon Enceladus, which still sports clean craters in its northern hemisphere. What if Tethys’s greater gravity pulls back the volcanic eruptions of this moon, giving the craters a smoothed, rounded appearance? What if Ithaca Chasma isn’t a side effect of the huge crater Odysseus (the flattened left edge of the moon in the image above) but a volcanic vent? What if we’ve become accustomed to Io’s hyperactive volcanism and we’re overlooking a more sedate single volcano or geyser on Tethys? It is a small moon, after all.
If you like your space images film noir style, check out this “raw image” featuring Enceladus, a “mystery moon” and Saturn with rings and ring shadow:
I think the smaller moon bottom right is Mimas, the innermost of Saturn’s major moons. Just for perspective, the larger Saturnian moons from close to farther out are: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, and Iapetus. Hyperion was the last of these to be discovered in 1848. All the others were first seen by human eye through seventeenth or eighteenth century telescopes. Saturn now has about 48 named moons and another dozen or so awaiting confirmation and/or official names.