A last Tethys post - I decided to add one more. Since I didn't map Tethys, here is a Cassini photomosaic used as a key to names of craters etc. from the USGS Planetary Names website. It's a start but it could use some aesthetic enhancements. There is a reference at the bottom right corner to a paper about this work.

https://asc-planetarynames-data.s3.us-west-2.amazonaws.com/tethys_comp.pdf

Tomorrow, a new thread for some more Voyager images of other moons. I think we'll start with Enceladus as Voyager saw it. #Saturn #Voyager #Tethys

The second image of Tethys shows a white circle, seen in better images to be a large impact basin called Odysseus. It was identified immediately in Voyager images. But there is a second large circular basin seen only in the image at left, lying under and to the right of that large valley (Ithaca Chasma). That was not noticed at the time and was only identified in these specially processed images:

https://www.lpi.usra.edu/meetings/lpsc2002/pdf/1553.pdf

A bit more on Tethys as seen by the Voyager missions. Here are two images, Voyager 1 on the left, Voyager 2 on the right. The best Voyager images were of the other side of Tethys. The dark streak is curious - it extends around half of the equator. Explanations in the journals include impacts by E-ring particles, electrons in the magnetosphere and ejecta from the two co-orbital moons of Tethys.

A closer image from Voyager 2 shows something of what's happening. Here Penelope has the shading we expect from sunlight - bright on the right, dark on the left. But it's subdued. The dark coating nearly balances the brighter sunlight. In the lower resolution image from Voyager 1 the two effects (albedo and illumination) cancel each other out and Penelope disappears. The dark material acts like it is sprayed on. Other topography shows the same effect. #Saturn #Voyager #Tethys

What's up with Penelope? Here are three images from Voyager 1, watching Tethys rotate. Penelope is in the left and middle images but where is it in the right image? And the shading on the crater wall - in the middle there should be no shading, the Sun's overhead.

Whatever that dark stuff is to the west (left) of Penelope, some of it has darkened the eastern (right) wall of the crater. The opposite wall of the crater was not darkened, as if sheltered from the dark material. #Voyager #Tethys

Here is a Voyager 2 image of Penelope, a prominent crater on Tethys. The processing here exaggerates albedo variations. If you were there it would look much less contrasty. The big crater is Penelope, and it looks pretty much as you would expect a crater to look, and like all the smaller craters seen best around the top of the disk. Sunlight makes one wall bright, the other is shaded. But that's wrong - look where it is. The Sun should be overhead. #Saturn #Voyager #Tethys

A few quick observations. We see dark markings in two areas, one running part way round the equator (top and middle rows), the other opposite it and more extended north-south. The second one is redder than the first (not visible in my B/W versions). Note the prominent crater Penelope in the top right image, the first in the 2nd row, and in images in the bottom 2 rows. There's something very peculiar about Penelope - as we will see tomorrow. #Saturn #Voyager #Tethys

On to Saturn's moons now. My intention was to get the most out of Voyager images before Cassini arrived. The best Voyager images are often seen but there are others with very interesting stories to tell. We'll start with Tethys. This image is a sort of index to the full imaging dataset for Tethys. Each image has been treated as I did for Ariel and Umbriel - the shading gradient caused by its spherical shape is suppressed and local features are enhanced. #Saturn #Voyager #Tethys

#Tethys Seas: 500 to 66 million years ago

About 300 Mya "a new ocean was growing, the Neotethys Ocean. The Central Pangean Mountains, due to the collision of Laurasia and Gondwana, reached their maximum height during the early Permian around 295 million years ago, comparable to the present Himalayas, but became heavily eroded as the Permian progressed."
Wikipedia CC BY-SA 3.0

A #map of Pangea and the Neotethys Ocean circa 290 Mya. Notice the enormous ridge at the collision of NAM and Gondwana: