Looking at the latest raws, expecting to see Titan, I saw this:

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=116647

That's pretty close!

Best pictures to date. These were from 36,000 km, on October 23 we will an even closer encounter at 25,000 km.

Images of Titan and Helene are underexposed again. Starting from this image of Dione taken on June 18, 2007, images are mostly underexposed. Why ? What is wrong ?

Don't draw a conclusion on the exposure from the raw JPGS. More likely is a bad stretching algorythm during the processing from data to JPG. There are too many links in the chain to assume a dark JPG is indicative of anything wrong with the operation of the camera.

Doug

I want to know : how do they stretch images from Raw to Jpg? What is the reason? They can't simply convert the raw data to jpg without apply a logarithm?

The great majority of Cassini's images have a 12 bit dynamic range whereas jpegs only have 8. There's also the fact low contrast targets such as Titan would be... well, low contrast without stretching. In a way, histogram stretching maximizes the amount of information present in the raw pages while having a neat side-effect of disallowing any meaningful analysis to everyone but the imaging team.

I second Doug's opinion the algorithm is messed up rather than a problem with the camera. It started around the time those T33 images were supposed to show up and never have (also that Kodak moment with Enceladus and Mimas in front of Saturn).

This is going to be a fabulous stereo pair between the start and end of the sequence...

Phil

Here it is...

Phil

Click to view attachment

Interesting how it has a much more cratered appearance than in previous coverage (which, admittedly was pretty unrevealing high phase).

Phil's great stereo pair seems to show a massive crater at the top of the image. I wonder, is this the same feature that is prominent in the low-resolution Voyager picture?

Yes, I believe it is. Also seen in some other views in this thread:

http://www.unmannedspaceflight.com/index.php?showtopic=3082

Phil

This is in response to Emily's request for suggestions regarding the irregular satellite size comparison on PS weblog. Mimas is included for scale as the smallest of the (roughly) spherical icy moons. I picked images of Prometheus and Pan within the ring plane because they seem to have a bit more detail. A key is included for visitors. The image scale here is approximately 330 meters per pixel.

Click to view attachment



Rude Commentary: To put this politely, gosh, I sure hope they can get better views of Prometheus some time...

EC, you da man! (figuratively speaking..) Your work never fails to impress!

I've never seen that image of Pan before, showing the same accumulation of fine grained ring material as does Atlas. Far from being a unique feature of Atlas, such could easily be common for large-ish moonlets embedded within, or skirting the edge of a dense ring system. I wonder if there are any high-res image sequences planned for Daphnis in the Keeler Gap?

EC, am I right in assuming the dark band over Pan is actually the outer edge of the A ring in front of the moon and not actually a dark feature on the moon?

Uhm, Pan appears to be too small in this wonderful rocks family portrait. The latest radii(km) appear to be

Atlas 22.8 19.0 9.6
Pan 17.6 17.3 11.5

Peter Thomas' latest figures as per the SPICE PCK kernel cpck_rock_19Apr2007_merged.tpc

Pan is only marginally smaller than Atlas. Atlas is a little more than 1/3 the size of Prometheus and Pandora which seems about right in the portrait.

EC: really nice comparison. It definitely helps to have approximately similar phase angles for all the moons being viewed -- that's one thing I need to work on. I actually have in the Society's website image database a big library of images of different solar system bodies at fixed scales -- 1 km/pixel, 500 m/pixel, etc. both up and down -- so any time I want to do a size comparison, I just query on the scale I want and up pops all the bodies for which I have images at those scales. I need to plug in some of the ones you pulled out here. Do you happen to have handy the PDS filenames of those images, or the raw image URLs, or their dates?

And pat -- would you be able to post the latest radii for all the little ringmoons? The diameters I have for my scale images are clearly off.

--Emily

I wonder how close Cassini could realistically get to Daphnis without getting sand-blasted during ring-plane crossing at periapsis; I'm thinkin' not very...

EC, beautiful stuff as always...this one is wallpaper-worthy!

Emily, try http://ciclops.org/media/ma/2007/2803_7468_0.pdf . Helene, not included, has radii values of 18, 16, and 15 km, though considering the last image set, it looks like the a axis value maybe a bit high due to a massif near 0 N, 350 W.

The LPSC paper Jason gives the URL for in the preceeding post ( http://ciclops.org/media/ma/2007/2803_7468_0.pdf ) has the current rock radii values

Thanks all.

--Emily

How big would Polydeuces be in comparison to the others? I seem to recall there being an image that resolved its shape.

Is anyone else struck by how similar the ridge on Helene is to the larger ridge on Iapetus?

Could the two have formed in a similar way, albeit at different scales?

Great work, Exploitcorporations! Here is that image with Polydeuces added as 13. I didn't feel like plucking letters to add it to the bottom.

Click to view attachment

Here is the Polydeuces image I used, taken on May 22, 2006.

Click to view attachment

Revisiting this thread and Phil's earlier stereo image made up from raw images, here's a calibrated IR3/GRN/UV3 crossed-eye stereo pair of Helene. Magnified 2x. Click to enlarge.



It's got some interesting, subtle color differences similar to what we've seen at Epimetheus recently.

I guess now that this Helene stuff has hit the PDS, I can show off this montage I did a year ago:

Whoah; that's another "face" right there.

(R27, image three, top row)

The Ciclops looking ahead article has been published for rev 94 see here and includes a flyby of Tethys (with stereo images to be acquired at around 60,000km of the southern hemisphere), and also another reasonably close pass to Helene at 65,000km.
The Helene images should be interesting, as Cassini is looking down on one of the poles (I'm unsure whether it's the pole with the huge crater or not)
Helene should appear in cassini's NAC field-of-view as rendered below using Saturn Viewer.

New image up on the raw page - seems like the aiming was off a little:

http://saturn.jpl.nasa.gov/multimedia/imag...ails174939.html

Slightly OT, but a Mimas Kodak shot followed: http://saturn.jpl.nasa.gov/multimedia/imag...6/N00124650.jpg