[X] My Assistant

[angel1801]

I have been using the solar system simulator alot on the July 23 Tethys encounter and from what I see, Cassini will be able to image all of the remaining bits of Tethys' south polar region that until has been poorly imaged.

Is this true?

[Phil Stooke]

Beautiful mosaics.

In the past I have suggested another explanation for the equatorial dark stripe - endogenic - but that was never a very strong argument. In the face of more recent observations of the Saturnian system (equatorial ridges on Pan, Atlas and of course Iapetus) it looks much more likely that this is another manifestation of the same thing.

Maybe Tethys interacted with a diffuse ring to accumulate this darker material. The quantity would be insufficient to do more than dust the surface, so there's no ridge. Maybe this was a coorbital destroyed in a catastrophic impact, forming a temporary ring in the orbit of Tethys. Eventually it accretes on the leading side of Tethys. Some images show that the dark stripe has a brighter central division. This might indicate a later icy rather than dusty ring doing the same thing, but I think it's more likely that it reflects a slightly inclined ring. Either that, or the ring itself was double, like the Jovian ring associated with Thebe and reflecting its orbital inclination.

Phil

[ugordan]

Great mosaics, Exploitcorporations! Your mosaics such as the second one and your Europa work is so crisp and sharp that it leaves me wondering how you pull it off! Also glad to see you back again.

Here's a little three-frame approx. natural color animation showing Tethys rotating. The sequence was acquired by Cassini on 20/21 Sep 2005. The first two frames were taken at a distance of 1.38 million km, while the 3rd one at 1.58 million km. The phase angles were 50, 58 and 56 degrees, respectively. Sub-spacecraft latitude was practically the equator (less than 1 degree latitude in all three cases) and the corresponding longitudes are shown in the animation. The rotation is roughly 70 degrees between each frame and, obviously, it's prograde so features disappear on the sunlit limb.
Narrow-angle red, green and blue frames were composited and enlarged 2x after scaling the third image to the same scale. North is approximately up (to within 5 degrees).


The sequence nicely shows a stark difference in albedo and color between hemispheres. Since the phases are roughly the same, the brightness variation can be approximated to be mainly due to surface differences.

This post has been edited by ugordan: Oct 25 2006, 07:50 PM