Yes, I must admit that the more I look at this the more I find the basins (or basin rims) case to be compelling.

Something else I'm noticing today is that the area to the west of the Voyager mountains looks interesting, with the western extension of the peaks having a more continuous and wavy look.

http://laps.noaa.gov/albers/sos/saturn/iap...cyl_070717b.jpg

Click to view attachment
Hmm, looks quite curious...
Maybe a kind of artifical effect in the way you are puzzling your maps ?
The eastern rim of the large basin also appears a bit wavy...

Bye.

Greetings T-A,

Good questions worth considering given the strange (or perhaps mysterious) appearance. For the wavy extension of the Voyager mountains, the original Voyager imagery had a somewhat similar appearance. I had at the time dismissed this as an artifact of the low resolution and being near the limb. The fact that the wavy appearance looks similar with higher resolution and less foreshortening (with Cassini - at least in the western portion of this feature as we move away from the limb) makes me think it is more real and therefore more intriguing. On the other hand the eastern portion of this feature in the original image is very near the limb and may be distorted in the map due to the higher elevation (a la mountain/bellyband extension). This is visible as a protuberance in the limb when I zoom way in on the rightmost crescent image. The Voyager image is also being mapped for part of this feature so you're right that this is a puzzle. Hopefully we'll see how this jives with the much better imagery planned for September.

The whole region at the western terminus of the "wave" is somewhat chaotic (like things were stirred up somehow) and after all is at the base of the "dark triangle" . Note also that I updated the map on 7/25 to clean up the region in question compared to the version you are showing.

The wavy appearance of the easternmost basin rim is somewhat affected by foreshortening. I believe it is real however as evidenced in the blinking GIF (post #149) comparing two of the October 2004 images, as well as the latest version of my map online where you can see the matching rim features in how the two images are superimposed. The rim top features in the lower sun angle image match very nicely with the shadows inside the rim in the higher solar elevation (thinner crescent) image. The current map version is at this URL:

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

I kept trying to convince myself that traces of "white" extending eastwards from the end of Cassini Regio past the big crater toward the white mountains at the west end of the Regio were a continuation of the belly band. I still see little or no real "EVIDENCE" in the saturnlit part of that scene, but keep seeing disconnected blurry traces of white parallel to the equator in that area. The new image data, horribly blurry as they are, really do seem to show that the white-mountains or some other expression of the belly band do extend westwards into that area. This implies that the bellyband is essentially continuous, though it may have been trashed in places by later craters, like by that big basin in eastern Cassini R.

Just a quick look tonight at Where is Cassini Now? looks like that Iapetus will appear to go directly behind Saturn as seen from Cassini. Granted that Iapetus is about as far away as it can get, any chances for some imaging of this event?

Here's another movie of an "ancient" Cassini flyby of the moon. Sixteen stretched color frames taken between 2005-03-14 and 2005-03-30 were processed to better approximate natural color. Closest approach was around 1.3 million km. Magnified 2x. No new terrain visible, it shows the hemisphere Cassini saw over and over and over again, but I like movies so...


Edit: there's a bit of a stereo effect to be had, seen here between the 1st and 3rd image in both a cross-eye stereogram and color anaglyph:

Awesome! Gordan, you're a machine!

That's a compliment so suitable for unmannedspaceflight.com

Hi,

let me just mention these three Iapetus far distance pics:
Click to view attachment

Nearly 7 million km - that's 1/8 of a close Mars opposition...

Bye.

It's 7 million km because that is twice Iapetus' distance from Saturn.

Cassini, right now, is where Iapetus will be in 40 days. They're on opposite sides of Saturn, at about the same distance. Cassini is one orbit away from closest approach, Iapetus half an orbit away.

The flyby's being set up.

For sure, I'm aware of this.
I just wanted to illustrate how large the saturnian system really is.
40 days of waiting for the most significant encounter of an icy moon since years.
Only the discoveries on Titan an Enceladus will match up with the spectacular images we'll see and the results we'll hopefully get, I guess.
Tension is rising...

Bye.

Btw., 9 additional far distance pics - including 3 showing Iapetus and Saturn - were updated on the raw images page.
Use 'Target Iapetus' for searching.

Bye.

Neat to see how things are setting up as we have 3 days or so until Cassini is farthest from Iapetus. During the next month we'll see the sunset terminator move from the eastern side of Cassini Regio to the western side as we transition from a gibbous to a crescent phase, as seen in this movie. Click to view attachment

We're closing in on Iapetus!
Images from yesterday are up!

Click to view attachment

I combined an IR, UV3 and GRN image to create a "color" image.
Even some Saturn shine is visible.

Click to view attachment

There's a rather neat "zero" phase observation from September 9, 2006 at the PDS. Here's an animation of 10 clear filter frames showing the opposition effect (click to enlarge):


And an IR3/GRN/UV3 color version of 5 frames around the time of lowest phase:


Both are magnified 2x.

If you notice carefully, Cassini Regio doesn't show as big an effect as Roncevaux Terra does. What could that imply about surface characteristics? Coarser grained stuff in CR?

Or would the grainier (snowy) material be in Roncevaux Terra with more small shadowed areas between grains that help contribute to the opposition effect? I would surmise then that CR is less granular, perhaps more tarry or something. The actual size of the grains may be less important in deciding whether there's an opposition effect.

It's quite possible, I was just trying to spark some discussion. Zero phase behavior difference seen here could be pretty interesting. I'm not acquainted with photometry and backscattering properties of different materials. My comment was based on the fact powdery surfaces (very beaten up regolith) seem to show the strongest opposition effect. It could just as well be dependant on the specific materials. The shadowing effect is only a part of the equation, coherent backscatter (if that's what it's called) is I think more important at zero phase. These shots seem to suggest CR shows very little of that effect.

Gordan - these are interesting animations that you put together, and yes there are several factors that can contribute to the opposition effect. I think there was a post (by edstrick) mentioning the morphology of some features in Roncevaux Terra suggesting grainy snow, so the opposition effect may lend more support for this. He also suggested the dark terrain was granular though.

I wonder whether there is more of an opposition effect on the bright side of Iapetus compared with other icy satellites? There is a general discussion by Sanna Kaasalainen in this thesis, particularly in section 1.4.3 where Anne Verbischer is mentioned:

https://oa.doria.fi/bitstream/handle/10024/....pdf?sequence=1

And this paper might be interesting to read if I had a subscription:

http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_...19_81_ns_nf_cjp

Beyond that, this gives me something to look for when walking around during the upcoming winter days.

Interesting PDF from a glance, thanks for the link. Regarding other icy moons, as far as I can see this is by far the lowest phase observation of any moon yet by Cassini (around 0.05 degrees minimum at disc center, comparable to the apparent angular diameter of the moon, 1.5'). I know there were some other low phase moon observations - Rhea comes to mind, but it was nowhere near this low a phase. Cassini did observe the rings at zero phase quite often, though. Earth-based observations such as the recent one are more favorable for catching several moons at the same time, but Cassini has the benefit of actually resolving the moons into discs.

Personally, I don't think Roncevaux Terra can come anywhere near Enceladus when it comes to the opposition surge. It's fairly bright albedo ice (comparable to Europa IIRC), but you can't beat the shiniest object in this stellar neighborhood. It might be interesting to compare it to Rhea on the other hand - similar albedos, but Rhea appears to be slightly dirtier.

Interesting. I would expect ice deposited as frost in a near vacuum to be very pure (hence bright), and in very small particles (hence high opposition surge) wherever it happened to be located. If Roncevaux is both less bright and shows less opposition surge than Enceladus I'd be inclined to attribute the differences to radiation damage rather than 'dirt' as such. That would be consistent with a very much lower deposition rate on Iapetus than on Enceladus - not unreasonable.

Below images from 17, 19 and 23 september together with simulated views (using Steve Albers' maps)

Click to view attachment

Nice views that you put together CAP-Team. One thing I'm working on is to try and soften the image edge on the map near the terminator in the vicinity of the central meridian in these views. One minor suggestion on the presentation would be to consider rotating the Celestia views (with certain keyboard controls) to match the orientation more closely.

It's interesting to backtrack to what we were looking at with the July 2007 imagery (Harkeppler in post #138) from a similar vantage point. For example the dark escarpment on the eastern rim of the western Claude basin was visible in those images.