So,
next Iapetus-image series released,
19 altogether, including 4 overexoposures.

Two Takeouts:

Date: 2006/04/10
Distance: 657.203 km
Filters: CL1 and CL2


Date: 2006/04/10
Distance: 622.761 km
Filters: CL1 and IR3

Closest approach is near...
Bye.

Greetings all,

I thought I'd mention my latest Iapetus map update. This has a rather preliminary inclusion of an image from the current April flyby. A previous update (from a week or so ago) has improved preprocessing of the Saturn-shine images yielding higher resolution and less cosmic ray hit noise.

Interesting to watch the current flyby and to select the best image portions for inclusion in the map.

The most recent map update is always at http://laps.noaa.gov/albers/sos/sos.html#IAPETUS

Here's a polar azimuthal equidistant projection of Steve's new map, south side only.

Phil

Hi,
Southpol view of the terminator on April 11th:


Bye.

Combination of a long unfiltered exposure (negative image) with green-filtered one:

Hi,
Some interesting structures are visible in your last picture, Marco:

orange box: equatorial ridge; its height is really enormous as the extend of the sunlighted part into the dark hemisphere supposes
blue quadrangle: large mountain
green circle: large impact crater
red lines: ridge on left side; maybe a rift/graben structure altogether
violet circles: mid sized craters inside this graben
yellow circle: eventually disturbed crater? Depth inside the graben?
Maybe april 11th images will show some more details...
The upcoming days will show a probable better illumination angle.

Bye.

Hi,
the closest Iapetus-series seems to be released, altogether 6 raw-images until now.

Here three takeouts:

Date: 2006/04/11
Distance: 606.161 km
Filters: CL1 and GRN


Date: 2006/04/11
Distance: 605.979 km
Filters: CL1 and CL2

GREAT SURPRISE...????
Eruptions also happening on Iapetus?
Or are these rays effects of scattered sunlight?

Bye.

Looks like JPL is having a hard time getting the saturnshine images to work, Unless they are attempting something else with these images?

I believe these images were taken this way for showing some kind of eruptions, fountains, etc., if they exist.
Therefore the rest of Iapetus is cut off.
Saturnshine images were nonsense to this date.
As said before Iapetus is showing his anti-saturn hemisphere.
Overexposured images were taken before to show features at the terminator, these two pics definitely don't.

Question to be answered:
True eruptions or effects of scattered sunlight?

And if eruptions do exist, where are they placed?
I may be wrong with the orientation of the image,
but it looks like they could be from the equatorial ridge -> western CR -> white peaks...

EDIT:
I tried to construct the local source of the rays:
(assumed CASSINI was oriented in the same direction, while taking both pics!)

Doesn't really look like western CR -> white peaks, at most the equatorial ridge...
Maybe we are just observing scattered saturnlight of the saturnshine-side of Iapetus...

Bye.

It's hard to say for sure, but my first guess is that the overexposed images might be an attempt to pick up some of the migration of water ice vapour from Cassini Regio towards Roncevaux Terra. Cassini's current position relative to Iapetus presents a good opportunity for that, since Iapetus is a crescent, and most of the part of Iapetus that we _can_ see is dark Cassini Regio material.

This ought to allow for really long exposure times before image saturation -- and long exposure times would be necessary to pick up something so faint. I've no idea how strong an effect this proposed migration is supposed to be, but, intuitively, it probably wouldn't be anywhere near as easy to spot as Enceladus' plumes.

It's difficult to tell whether that "wispiness" in the overexposed images is just a result of the overexposure or something real. It might be worthwhile to make a movie of those images in chronological order. That might give a clue as to whether we're seeing a physical process. It wouldn't be proof, but it would be half decent circumstantial evidence.

[Edit: Over the next few days, we might get another clue. One would expect that, if the water ice vapour were visible to Cassini's cameras, it might appear to be a bit denser on the Saturn-facing part of the sunlit side, because it is "afternoon" on that part of Iapetus at the moment, while the part we're seeing right now is experiencing "morning". Thus it should be a few Kelvins warmer on the Saturn-facing side and we *might* see a greater density of evaporated "wispiness" there. As Cassini moves behind Iapetus, it will be well positioned to see something like this happening. If it's happening. This is total conjecture on my part, of course.]

In other news, that south polar region seems to be turning up a lot of neat stuff. Of course we have to remember that any vertical relief close to the terminator is going to be really, really obvious, but it's still an interesting patchwork-quilt. I hope we will get a better look at it during the September 2007 close flyby.

It's funny. If I use my imagination, what that area reminds me of a little is Miranda. There's a sort of chevron, and a zig-zag mountain. But if this pass has convinced me of anything, it's that there's no substitute for improved resolution.

Michael

Those rays are probably stars. The long exposures let the star tracks run for a distance across the image. Note that the lower end of all of those tracks have the same squiggles in them.

Well, of course the diagonal streaks are stars, but what is the wispyness extending upwards? It doesn't really LOOK like a camera artifact, look at how it kinda bends and isn't rounded.

I don't see the "bending" you refer to, but I don't think camera artifacts would be incapable of having a curved appearance.

My guess, for what it's worth, is that the "wispiness" we are seeing is due to overexposure (I'm not referring to the star trails here) since migration of water ice should be more of a global phenomenon rather than a regional one. The overexposed images might still be an attempt to spot migration -- but, if that's true, it doesn't mean the attempt was a success.

Also, it's tough to imagine how Iapetus could have plumes. Even if an energy source could be found, the moon's overall ruggedness and the dark albedo of Cassini Regio seem incompatible with any long term geological activity, or ongoing "snowfall".

I have checked the "Solar System" simulator for Iapetus around September 12, 2007 and I have some good news. Iapetus's south pole will be visible. However it will be at the very bottom of any global (whole disk) images and therfore not be optimally imaged. I hope that there might be a slight change to the flyby sequence to improve the imaging of the south pole more optimal.