Presumably these images show Tethys fully sunlit. So what are the other light sources producing the topographic shading? I'm guessing the principal secondary souce (from the left) must be Saturn, but on the right side the craters are shaded the other way, suggesting a third source.

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=203206

Looks like low phase images with only sunlight providing illumination and shading.

For the first time for some months Cassini has obtained lots and lots of nice icy satellite images.

New and spectacular images of Tethys, Mimas, Enceladus and Rhea have appeared on the raw images page. The Tethys images probably the most spectacular low phase images of that satellite I have seen. Tethys' variable albedo is very obvious, especially in the UV images:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=203206

There are also interesting low phase images of Mimas:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=203179

Enceladus' plumes:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=203119

And finally, Rhea:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=203139
http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=203110

I wonder if there's more to come since the 203110 image of Rhea is the only one taken at really close range.

That's odd Gordan, I really can't agree there. The illumination of that central crater is clearly asymmetric. it doesn't look like an ordinary 'full moon' picture at all.

It's interesting to compare these new images of Tethys to e.g. this one:

http://photojournal.jpl.nasa.gov/catalog/PIA08149

In the new images north is down and Saturnshine is coming from the right but sunlight and the effects of topographic shading and albedo markings dominate. In particular, in these images the right half of Tethys simply has a lower albedo than the left half. And there can't be a third lightsource.

Precisely. And any additional light source would be orders of magnitude fainter than sunlight so it would be rendered inconsequential.

The shading of some of the craters is due to the dark deposit, we saw the same effect of the northern parts of Iapetus in the first flyby where the northern sides of the craters were dark reversing the typical shading.

I have attached an image with two boxes. From what you both say (I didn't think you could be wrong!) the crater shading in the big box is due entirely to albedo variations. That leaves the craters in the small box which appear to be shaded the opposite way. Is that an albedo effect also, or due to the Saturnshine from the right?

2002 (pre-cassini) report on the same phenomenon...

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

Phil

(PS from Ngunn's post: the two boxes are on opposite sides of the broad dark stripe... it's dark stripe material coating stripe-facing crater walls on both sides)

Thank you all! My imaginary light sources have been dispelled by genuine enlightenment.

I checked the Mimas image and didn't see these effects - which all makes sense now.

Looking at the Tethys mosaic map there is no sign of the dark stripe. In fact the illumination angle in the images used there seems to mask the effect entirely. Presumably these new observations will be very helpful in improving the map.

That new Enceladus image is beautiful.

Beautiful!! - I think there may be more Rhea mosaic shots to come.
Frustratingly, the raw image pages have stopped posting the range at which an image is taken in lots of cases (e.g. 80,171km or whatever) does anybody know why?

Jase

The darker area near 270W does appear to show some in my map. The official map might be doing some hi-pass filtering that would suppress albedo variations. There are some interesting color variations just east of here as well. Dr. Shank's map shows the albedo and colors pretty well in enhanced form.

That is pretty neat about the shadowing effect of dark material emplacement. The challenge here would be to add this in from low-phase low-res imagery together with hi-res and higher phase angle images. At least some additional hue information from the new color imagery might be worth inserting. The reverse effect seems to disappear once we leave the UV band or go to higher phase angles.

For reference my latest map is here:

http://laps.noaa.gov/albers/sos/sos.html#TETHYS

Steve

Yes, beautiful images. To me the image of Enceladus is completely stunning. Saturn shine illuminating the disc just enough so we can see detail on the disc and also see the plumes. One of the defining images of the whole Cassini mission! What a world! How unexpected! So I think it's worth posting the actual image here.

Click to view attachment

I just love having the privilege of downloading these new images as soon as they come out!
Here's a UV/G/IR-1 color composite of Tethys from the 15th combined in MaxIm DL CCD.
Click to view attachment

Mamma! That's making my head spin!

What an entrance S_Walker! Welcome...

Thanks!

I've been doing this and mosaics for a few years in Sky & Telescope to get images "hot off the press", and only got tipped off to this site by Emily Lakdawalla in an article that readers will enjoy in the January 2010 issue due out next month.

Keep up the great work here people!

Sean Walker
Imaging Editor
Sky & Telescope

I will look for the Jan. issue. The quality of the image is amazing.

The Tethys color image is beautiful... and note that it has small dark spots on it in several places. Some of them were visible in Voyager images, and are illustrated in that LPSC abstract I linked to a few posts above. But more can be seen here.

Phil

In regards to the Enceladus picture...

A detail I find interesting here is that the night limb of Enceladus is DARKER than the background sky. I am surprised that there is that much scattered light from the tenuous ring (or extended exosphere) derived from the plume.

--MarkG

Here's a mosaic of four images of Tethys taken with the narrow angle camera and green filter. Higher resolution. I'm hunting down the corresponding UV and IR images to see if i can make a large color version.Click to view attachment

The shading looks more consistent across the above image being at a slightly higher phase angle.

In the earlier color image it gets tricky for mapping since the blue color at the edge may be partly photometric in origin meaning it appears due to grazing incidence. It may look less blue from an overhead vantage point. This was mentioned somewhere on the CICLOPS release captions I think.

Looking forward to Sean's color version of the mosaic if the images are there.

Final UV/G/IR mosaic from 10/15. Interestingly, the dark spots aren't visible in this data set... however, these were less overblown that the widefield color data. Click to view attachment

Nice!

Here are two composites of Rhea from the new data; the first uses IR1Click to view attachment, G, and UV3.
The second is a ratio image made by subtracting the IR3 from the UV3 image to show the potential ring material impacts noted earlier this month.

Click to view attachment

Beautiful work! Sean, welcome to UMSF!

Thanks Ted.

Question: what software package are you using to align mosaic pieces with? I use a number of them, including Photoshop CS4, MaxIm DL, and occasionally RegiStar (works great on battered moons, but not smooth features like gas giants).

On the 4-frame Tethys mosaic, I registered the UV/G/IR frames with Registar, then merged the color mosaic with Microsoft ICE. It would be nice to have something where I can assign multiple alignment points with...

Sean

Adding to that last point... I could really use a good image warping app - one that lets me use a large number of points for complex warping. Right now I do it in a GIS, but a simpler and cheaper method would be really appreciated. Anybody know one?

Phil

A really nice series of images of Tethys, the rings, and one of the smaller moons (need help here identifying it). Would make a great movie.

I think it's Prometheus, but it doesn't seem to be in the predicted place
Click to view attachment

There are two moons visible. One could be Prometheus/Pandora, the other one Janus/Epimetheus.

Jay Mayor running Lights in the Dark animated that sequence.

Wow! Thanks ugordan, now I finally see the third moon (wasn't in very many frames--so that is how I missed it). Edit: Thanks for the link to Jay Major's excellent image of the day site.

Beautiful and stuning images you made here .

Joining the party to show you Encelade and its plume, in color :

This belongs in the Louvre, Ant!

Beautiful Ant! And now for you, here is the French version:

Thanks for the notation here! Glad you like the site.

Phil - Unsure how cheap this would be, though IDL can accept a large number of tiepoints for warping. I used about 60 in a Europa map a while back. Of course one can also warp an image of simple shaped objects by using map projection equations/routines.

GDL is a freeware version of IDL that may work on a Mac.