Just giving you guys a heads up that a new set of Iapetus observation should be on line soon on the Raw Images page. I don't know whetther they will have the stretch working by then. If they are released and the stretch is bad, I'll redo them for you guys. These provide a great view of a giant crater in Cassini Regio (I'm wondering if this is a different crater. It looks about 350 km across.

Thanks, volcanopele -- I really appreciate your keeping us all informed.
I'm looking at image N00006752 of Iapetus -- I'm not sure if this is one of the images you're referring to or an earlier one -- but I see not one but three huge splats in part of Cassini Regio, forming a sort of right triangle, at least one of which has what looks like a flattened central peak. The crater toward the bottom of the image actually seems to cross over the dark/light division on the moon. Illusion?
(It would be helpful if I could say north, south, east or west, but I'm not sure that I can accurately project the coordinate systems of current maps onto what I'm seeing. I'm guessing that the crater at the boundary of Cassini Regio is Marsillon, but I'm not sure -- I'm finding it hard to identify the two prominent craters at the terminator, which ought to show up in one of the Voyager images.)

North is to the right, so the crater near tthe bright/dark boundary is not Marsillon.

I just checked the raw images page and the new set isn't up yet. They were returned from the spacecraft yesterday so it may be a day or so before they are posted.

Are these images being taken to fill gaps in coverage from Voyager or to look for changes that have occurred since the Voyager flybys?

The new Iapetus (post-solar conjunction) observations are now up. Here is an example:

http://saturn.jpl.nasa.gov/multimedia/imag...2/N00006752.jpg

The stretch is great for looking at the features in Cassini Regio, but not elsewhere. I'll post a restretch later today.

These observations are meant to fill a gap in Voyager data.

Clicking on "Browse Latest 500 RAW images" doesn't always bring up the latest pictures.

If I click on "Narrow Angle" and then "search" there are some new pictures of Saturns south pole.

Also, regarding the "stretching" of images, why not simply convert them straight into JPEG without any further modification?

I managed to dowload one of the MER RAW images from the PDS archive and view it with "NASA View" it allows you to save the IMG file in GIF or JPEG. The jpeg doesnt look any different to the original.

I cna confirm that this is a different crater we are seeing in these new images from the giant one seen in image I posted last week. The previous crater is in the eastern end of Cassini Regio while this one is more in the middle. The previous crater is in the ball park of 500 km across while this one is 325 km across. There might also be a similar sized crater south east of it

I see now.

They try to apply a consistent stretch which works if the target fills the field of view but doesn't when you have targets that fill < 10% of the field of view like these.

Are you all noticing any changes since the Voyager flybys? Is Cassini filling in gaps from Voyager?

I'm not seeing anychanges though these are intended to be for gap filling, not change detection. With such a cratered surface (both inside and outside Cassini Regio) I wouldn't expect any.

Now here is the big question, how did the heterogeneity form on Iapetus. Both albedo areas appear to be heavily cratered with Cassini Regio having at least 2 (maybe 3) large impact basins.

If both sides are equally cratered, one would expect that the dark or light "layer" is only very thin. (wich one is the "layer" and which one is the original surface, or are they both layers on top of an original surface)

two things I can think of:

- stuff is deposited on the leading side
- stuff is eroded on the leading side, revealing darker material beneath

but I'm not an expert at all. do these guesses seem reasonable? Are there other possibilities?

That's a good question, I don't see any large impact basins on the bright "side", just on the dark side. Maybe we have been thinking this all wrong and in fact these icy satellites have dark interiors that these large impact basins are bringing up. jrehling (does he come to this forum?) has a good theory on that and I for one and beginning to agree with him.

what is his theory?

that the giant craters dredged up dark material from deep within Iapetus.

I do not use NASAView but it seems to me it must be stretching the MER images because when I look at the images without any processing the intensity of the images typically ranges from 0 to about 3000. However, these are 16 bit/pixel images, equivalent to an intensity range of 0 to 65535. So without any processing the images appear almost black and I assume you wouldn't be saving black images to GIFs or JPGs ;-).

More on-topic: Jason, do you know if improvements are likely to be made to the stretch algorithm used for the raw Cassini images ? Because as has been discussed here, images where the target fills only a small part of the FOV are usually unusable.

The problem is that I have no idea who to bring it to. My first guess is Carolyn, but my understanding is that she isn't too happy about the immediate release of raw images as it is so whether she would have it taken care of or put on the back burner is a big question.

http://www.nasa.gov/mission_pages/cassini/...a/pia06100.html