Most of Saturn's nine largest moons have some characteristic that distinguishes them from the others, by which I can more or less instantly recognize them when I see their images:
Titan is big, orange, and smoggy
Iapetus is pied black and white, with an immense crater, irregular shape, and that wacky equatorial ridge (almost too many weirdnesses for one moon!)
Enceladus is small, icy, and smooth like a spherical hockey rink, with those warm antarctic catscratches
Mimas is small, bumpy, egg-round, with a really big crater
Hyperion is irregular and pocked full of medium-sized black-bottomed holes
Phoebe is potato-shaped with a less dense pocking of conical craters, plus a few larger ones
But the three I still have a lot of trouble distinguishing are Rhea, Dione, and Tethys. I know Rhea is considerably larger, but the scale difference isn't enough to make it a lot less lumpy than the other two, so that doesn't help much. What distinguishing marks should I look for to be able to easily differentiate these three moons?
Tethys: Ithaca Chasma and the huge Odysseus crater. Apart from this, lots of craters.
Dione: Its albedo varies a lot more than Tethys'. Bright features with a 'wispy' appearance in long-range images. No really big craters or 'canyons' as in Tethys' case.
Rhea: Fairly uniform albedo, no really big craters or canyons and its 'wispy' features are far less prominent than Dione's. *Lots* of craters.
Rhea is hardest to identify, since it lacks prominent special features. However, its craters are somewhat angular and less deep compared to Tethys or Dione so close-ups make identification easier.
Tethys and Dione are easy to identify when you see their special features. Dione is also darkest of the three, so it is easier to distinguish from others if it is in same image with another moon.
Tethys: smaller than Rhea, rugged terrain, Odysseus and Ithaca Chasma prominent, look for Penelope-Phemius-Polyphemus-Ajax grouping of craters
Dione: Prominent wispy terrain on dark background, smoother topography than Tethys elsewhere, south polar impact basin
Rhea: Two large impact basins in anti-Saturnian hemisphere (Tirawa and ... S. Tirawa), ray crater, rugged like Tethys but bigger, wispy terrain with lighter background than Dione's and with fewer "branching arms", Two impact basin south and east of wispy terrain (Izanagi)
That Cassini probe sure knows a photo op when it sees one:
http://www.universetoday.com/am/uploads/2005-1110threemoons-full.jpg
As wonderful as the Voyagers were, Cassini is proof positive that a couple of flybys just are not enough.
MOONS IN PERSPECTIVE
--------------------
Two of Saturn's battered, icy companions hover here in this Cassini image,
above the planet's ringplane. To get a sense of the three-dimensional
nature of the scene, note that the wide band of visible rings is in
between the two moons in this view. Mimas is outside the far side of the
rings. Dione is outside the rings and closest to Cassini.
http://spaceflightnow.com/cassini/060123moons.html
Three moons, quite artistic/epic:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS18/N00049538.jpg
Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)