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Imaging Diary - Cassini
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| Craters and Chasms on Tethys - Sep 29, 2005 | | | A recent tweak to Cassini's trajectory allowed an even closer approach of 1,500 kilometers (930 miles) to the Saturnian moon, Tethys, than originally planned, and yielded unrivaled views of the icy moon’s cratered landscape and a look into the gargantuan canyon system called Ithaca Chasma. |
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Alliance Member Comments
Spotlight on Penelope |
carolyn 2009-11-16 15:24:20 | View all member's comments | 20Tauri and PolishBear: The reason why Tethys is so bright is BECAUSE the phase angle is near zero. All the solid, airless bodies in the solar system, even the rings, show an increase in brightness near zero phase called `the opposition surge'. (See the opposition effect on the rings in http://ciclops.org/view.php?id=3280 , and ignore the `rainbow' because that's an artifact.) It's a well known observational phenomenon and has its origin in 3 different effects. One, the roughness of the surface will not produce shadows at zero phase (or thereabouts), as it would at other phase angles, because the sun is directly behind the observer: that's what zero phase means. Second, one particle or body on the surface won't cast a shadow on its neighbors at or near zero phase, either. Third, there is something called 'coherent backscatter' which is multiple light scattering that occurs between microscopic grains on a surface that is observable very close to zero phase. The opposition effect can be seen in images taken of the Apollo astronauts of their own shadows: the surface immediately surrounding the astronaut's shadow is peculiarly bright. Anyway...more than you probably bargained for, but that is why Tethys is so bright in this nearly fully illuminated geometry. | |
Spotlight on Penelope |
PolishBear 2009-11-16 10:25:40 | View all member's comments | DEAR 20TAURI:
The density of Tethys is 0.97 g/cm³, indicating that it is composed almost entirely of water-ice. Its surface is one of the most reflective (at visual wavelengths) in the solar system, with a visual albedo of 1.229. | |
Saturnscape After Equinox |
NeKto 2009-10-05 11:55:27 | View all member's comments | i like the clearly visable light demarcation on Tethys. i won't call it a terminator because i see so much illumination from Saturn shine. makes it easy to determint the Saturn side. | |
Shadows Big and Small |
Red_dragon 2009-08-24 13:07:17 | View all member's comments | Simply put, amazing. Not only the geometry, but also to see stars through t he rings. And if Tethys' shadow was in the middle of the rings would be even more impressive.
Although this has not much to see with Saturn, I'd be pleased if you asked me about this: we know asteroid belts as appear on sci-fi movies, etc. are innacurately represented and perhaps the closest thing to them would be Saturn's rings or the like.
But what about a protoplanetary disk?. Could it look like as for example the asteroid field of "The Empire Strikes Back"?. Thanks in advance. | |
Side by Side Shadows |
Red_dragon 2009-08-10 14:24:41 | View all member's comments | Excellent image. The best is to see how the shadows of both Saturn and Tethys run parallel one to each other.
After this one, this other is a must, even more than usually: http://ciclops.org/view/2563/Ring_World | |
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