Emily Lakdawalla • Jul 26, 2007
The best view of Helene yet
Cassini's current orbit has been a great one for the imaging of Saturn's icy satellites; there have been lots of images of Tethys, Dione, Enceladus, Hyperion, and a bunch of mutual events of various moons with each other and/or Saturn and its rings. However, the most unusual item is Cassini's closest approach yet to Helene. Helene is a very small moon, a lump approximately 36 by 32 by 30 kilometers in size. Unlike most of Saturn's smaller moons, this one isn't close to the rings; instead, it orbits among the much larger round satellites. This one sits in Dione's leading Lagrange point ("L4"), a position 60 degrees ahead of Dione in the same orbit where the gravity of Saturn and Dione balance each other. (There is also a trailing co-orbital named Polydeuces.)
Just to set up the context, here's the best image we had of Helene before Cassini arrived. I went in to the newly calibrated and geometrically corrected Voyager Saturn data set on Helene to get this one, not that it mattered very much; Helene is only a few pixels across, and not much is visible except that it's lumpy and has at least one really big crater.
For a better sense of the topography, here's a crossed-eye stereo pair. To see the 3-D view, stare at one and cross your eyes until the two images overlap in the middle of your vision, then try to focus your vision to get the crossed image to resolve into three dimensions.
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