[X] My Assistant

[TritonAntares]

First of all, again the two existing encounter animations:
Animation 1
Animation 2

Nearest approach:

Resolution about 3,6 km/pxl.

And some pre-info about upcoming encounters:
2006 Mar 25 to Apr 18: Apr 11 - 602.412 km; 14-3.6 km/pxl; medium to high phase, southern hemisphere as crescent
2006 Jun 17 to 27: Jun 23 - 1.343.000 km; 14-8.1 km/pxl; medium to low phase, sub-Saturn hemisphere
2006 Sep 08 to 09: Sep 02 - 1.816.000 km; ~20 km/pxl; zero phase (3 to 0.05 deg), sub-Saturn
2006 Nov 26: 1.997.000 km; 12 km/pxl; very low phase, sub-Saturn
2007 Feb 12 to 15: Feb 14 - 2.249.000 km; ~14 km/pxl; sub-Saturn; very low phase and eclipse
2007 Apr 14: 2.256.000 km
2007 Jun 22: 1.817.000 km; ~14 km/pxl; med. phase, trailing side
2007 Sep 03 to 09: 8.6-0.7 km/pxl; very high phase, western Cassini Regio
2007 Sep 10: 480-10-540 m/pxl; targeted flyby, trailing side
2007 Sep 11 to 17: 0.7-7.1 km/pxl; low phase (~33 deg) trailing side
2007 Sep 27: 15 km/pxl, low phase sub-Saturn+trailing side
2007 Nov 26: 1.371.000 km; 8.2 km/pxl; very high phase, north pole, possibly graylight
2008 Feb 13: 2.045.000 km; 14 km/pxl; high phase, north pole, possibly graylight

Days around Sep 10 belong to the targeted fly-by in about 1000 km distance,
others will only be some OPNAVs.

Bye.

[TritonAntares]

First of all, again the two existing encounter animations:
Animation 1
Animation 2
...

I've forgotten a third one:
Animation 3

Not so nice concerning the drawn textures, but showing dates and distance data.

I've tried to create an additional one with 'Celestia', but I came in trouble with zooming in from Cassini to Iapetus.
Also I did a mistake in using Steve Albers latest map. It's centered on 0°, not on 180° as 'Celestia' wants.
So I was quite surprised in seeing the equatorial ridge with its white mountains in prime focus at end of this month...
Is anyone able to convert it into the 180° seight? 1024 x 512 pixels would be sufficient.

Alternativly is this map from December:


'Terra incognita' is shown in black...
but not so nice as Steves' map.

Thx and Bye.

[angel1801]

I've forgotten a third one:
Animation 3

Not so nice concerning the drawn textures, but showing dates and distance data.

I've tried to create an additional one with 'Celestia', but I came in trouble with zooming in from Cassini to Iapetus.
Also I did a mistake in using Steve Albers latest map. It's centered on 0°, not on 180° as 'Celestia' wants.
So I was quite surprised in seeing the equatorial ridge with its white mountains in prime focus at end of this month...
Is anyone able to convert it into the 180° seight? 1024 x 512 pixels would be sufficient.

Alternativly is this map from December:


'Terra incognita' is shown in black...
but not so nice as Steves' map.

Thx and Bye.

I (out of interest as "Celestia" is referenced here alot), decided to download it. I was not happy with the textures they used for Saturn's moons, so I decided to use Steve Albers maps. And I can get them to work.

Here's how. Copy his maps to the "textures --> hires" folder and remove anything after the body's name on the file name. ie "Tethys_www_cyl_rgb" to just "Tethys". Do the same for all the other "Hires" textures. When you load Celestia, choose "Hires" mode and select the maps you have just loaded.

And to solve the problem with the maps being centered at 180W reather than 0W, just do a mental calculation to adjust for the problem.

ie To have the "The Great White Splat" (12S, 111W) centered on a Rhea Map, select -12 for latitide and 69 for longitude.

69 = -111 (=111W longitude) + 180

Another example "Tirawa" centered Rhea,

Latitude = 34.8 (34.8N)
Longitude = 28 (-152 + 180) [-152 = 152W]

Again using Rhea, "Evil Twin" (10N, 180W) would be imput as +10 latitude and 0 longitude.

I have collected a wonderful collection of Saturn's moons and and a variety of views. I have got polar views (centered on both north and south poles) for all of Saturn's moons that I have a good map for (provided by Steve Albers of course!)

Of course, the pole centered maps need no adjustment.

ie Dione centered 90N and 0W is simply entered unadjusted.

90 for latitude and any input longitude.

I hope this helps you.

[scalbers]

Hi all,

It's true I use a map convention that's 180 degrees offset from Celestia. I actually routinely port my map updates into Celestia. To do this I (in a Linux environment) run the 'convert' utility with a "roll" option to offset the map. There may also be a way to make a Celestia animation that can be posted on the web, though it may be a bit tedious. Here are a couple of still images:

http://laps.noaa.gov/albers/sos/saturn/iap...tus_apr06_1.jpg

http://laps.noaa.gov/albers/sos/saturn/iap...tus_apr06_2.jpg

[angel1801]

Hi all,

It's true I use a map convention that's 180 degrees offset from Celestia. I actually routinely port my map updates into Celestia. To do this I (in a Linux environment) run the 'convert' utility with a "roll" option to offset the map. There may also be a way to make a Celestia animation that can be posted on the web, though it may be a bit tedious. Here are a couple of still images:

http://laps.noaa.gov/albers/sos/saturn/iap...tus_apr06_1.jpg

http://laps.noaa.gov/albers/sos/saturn/iap...tus_apr06_2.jpg

Is there a "roll" option for those who use Celestia only on Microsoft Windows? Can you write a script
in Celestia for Windows to compersate for it?

[helvick]

Is there a "roll" option for those who use Celestia only on Microsoft Windows? Can you write a script
in Celestia for Windows to compersate for it?

I don't think celestia can do this itself but you can also do this with any graphics editor that can load the files - just carefully split it in two and rejoin by hand.
I have a short Perl GD script that I can post that does it but you'd need Perl with the GD module installed for it to be of any use to you.

[scalbers]

Angel1801,

It turns out that the 'convert' utility is independent of Celestia, so I simply run this prior to copying the file into my Celestia directory. Perhaps there's a similar utility available in the Windows environment, within Photoshop or something like that?

Another option is that I might be able to mirror some of my Celestia map versions to a web-accessable directory. Hopefully the disk space would be reasonable, though if that were an issue I could always run my 2-week purger on it (relative to when I update a given image). I'll think about this some more over the next few days.

[Phil Stooke]

If you need to switch between maps centred at 0 and 180 longitude, the process is trivial in any image editing software like Photoshop. I would simply select the whole map, copy it and paste it over itself twice. One copy I push out half-way to the left, one half-way to the right, then zoom in and make sure they are exactly lined up with each other and with the middle column of pixels. Flatten and save.

Phil

[um3k]

If you need to switch between maps centred at 0 and 180 longitude, the process is trivial in any image editing software like Photoshop. I would simply select the whole map, copy it and paste it over itself twice. One copy I push out half-way to the left, one half-way to the right, then zoom in and make sure they are exactly lined up with each other and with the middle column of pixels. Flatten and save.

Phil

You can also use the "offset" filter. Just set it to offset it 1/2 the pixel width of the image to the right. (I hope that made sense. I'm a bit tired.)

[edstrick]

I flipped the meridians in an Iapetus map a while back in photoshop by using the "Image / Canvas Size" command: I reduce the image by half horizontally, cropping the right side and saving the file as "left". I reload the image and then repeat the process, cropping the left side, saving it (for safety) as "right". I re-size the canvas to enlarge the right, open select and copy the "left" image and paste it in the blank "right" area. Probably need to "flatten" the composite image.

I've never figured out how to use layers and stuff worth a damn. Lazy.

[TritonAntares]

Many thanks for the advices on converting the Iapetus-map from 0° to 180° center.
I will try when time allows...

Back to Iapetus...
...I found these two 'old' Cassini images back from July 19, 2004:


Distance: ~ 2.9 Mio. km
Resolution: 17 km/pxl

A first hint on what we'll see in the upcoming far-encounter.
Visible is the bright southern rim of the big bassin in eastern CR
and the polar region with a large amount of craters below.
Actually what is the dark curved structure parallel to the terminator?
The eastern rim of another big bassin?
There also seems to be a greater structure - possibly a crater - left to the terminator south of this dark bow.

Bye.

[scalbers]

Interesting images from back in 2004. I'll have to see whether they add any details beyond what I have in the map.

I have also placed some Celestia compatable versions of the Iapetus map on the web at this URL:

http://laps.noaa.gov/albers/sos/celestia

[TritonAntares]

You can also use the "offset" filter. Just set it to offset it 1/2 the pixel width of the image to the right.

I tried this...
and easy going!

Here are 3 animations for the upcoming far-encounter using this texture:
Mar 25 to 31:
 iapetus_a.avi.html ( 215.5K ) Number of downloads: 1651

Apr 01 to 12:
 iapetus_b.avi.html ( 425K ) Number of downloads: 1360

Apr 12 to 18:
 iapetus_c.avi.html ( 272K ) Number of downloads: 1356

Just remove *.html and run the avi-files.
I prefer running them on a DIVX-player.

Bye.

[tedstryk]

Many thanks for the advices on converting the Iapetus-map from 0° to 180° center.
I will try when time allows...

Back to Iapetus...
...I found these two 'old' Cassini images back from July 19, 2004:


Distance: ~ 2.9 Mio. km
Resolution: 17 km/pxl

Yes...that is a sequence from slightly farther out than the one I used to make this super-res view I posted a while back.

[TritonAntares]

The first Iapetus image of the upcoming far-encounter has been released by NASA/JPL:
Here an enlarged part:

Date: March 16, 2006
Distance: 5.247.271 km (!)
Filters: CL1 & CL2
Enlargement: 3x

Don't know why they took it, probably an OPNAV.
Maybe they just wanted to know if this strange moon is still there...
... it is.

Bye.

[Decepticon]

To lazy to to check, is Iapetus in a proper orbit for saturnshine images?

[ugordan]

To lazy to to check, is Iapetus in a proper orbit for saturnshine images?

There is no "proper" orbit for saturnshine images. Every orbit will carry the moon over Saturn's dayside eventually, if it's a circular orbit it will do so for half the orbital period. This is the time when the sub-saturnian hemisphere of the moon receives saturnshine. The brightness obviously depends upon distance from Saturn and the phase angle at which Saturn appears.

[TritonAntares]

Yes...that is a sequence from slightly farther out than the one I used to make this super-res view I posted a while back.

I created a simulated Iapetus view with Celestia for Jul 19, 2004:



Maybe I'll add an animation later.

When actually was your super-res taken?

Bye.

[tedstryk]

I created a simulated Iapetus view with Celestia for Jul 19, 2004:



Maybe I'll add an animation later.

When actually was your super-res taken?

Bye.

I will have to research that. I lost the work in my computer crash, and I only have the finished product because I posted it to this forum and downloaded it again...Without the original files, I can't say for certain which images I used, although I know I used an entire set and that it was the closest set I could find taken prior to orbit insertion.

[scalbers]

I did a Celestia run for July 2004 and found that Cassini had a closest approach at about 0900 UT on July 13, and this just about matches Ted's super-res image! I am currently checking to see if this can add detail to my map. This image really does seem to have a lot of detail for 2330000km distance.

Ted, I was unable to spot the original images on the raw images page, so perhaps you had done your processing using PDS images?

[TritonAntares]

..., I was unable to spot the original images on the raw images page,...

Hi Steve!

Try this one:
http://saturn.jpl.nasa.gov/multimedia/imag...feiImageID=7174
...and the following images.

Quite a lot of stuff I've never had a detailed look at...

Bye.

[Decepticon]

Images stared coming in... http://saturn.jpl.nasa.gov/multimedia/imag...9/N00056025.jpg

[TritonAntares]

Hi,
yes, the first 18 images arrived.
Here two takeouts:

Date: 2006/03/25
Distance: 2.375.054 km
Filters: P60 and GRN


Date: 2006/03/26
Distance: 2.325.426 km
Filters: CL1 and CL2

Nothing spectecular, the same side as everytime...

Bye.

[TritonAntares]

Hi,
another 9 images were published.
Here one takeout:

Date: 2006/03/27
Distance: 2.262.603 km
Filters: CL1 and CL2

Bye.

[TritonAntares]

Hi,
Here a Iapetus picture gallery from the German FU-Berlin.
Some images were unpublised until now.
Bye.

[Decepticon]

Those night side images are just breath taking!

[Guest_BruceMoomaw_*]

Keep in mind that they're NOT the nightside; they're the dark side (Iapetus being the only moon that genuinely has one).

[tedstryk]

Keep in mind that they're NOT the nightside; they're the dark side (Iapetus being the only moon that genuinely has one).

Actually, in that series, there are several that are from the Saturnshine coverage.

[mchan]

Keep in mind that they're NOT the nightside; they're the dark side (Iapetus being the only moon that genuinely has one).

Hmm, I had never considered before that Pink Floyd was referring to Iapetus.

[TritonAntares]

Hi,
ever seen this series?

This enormous southern bassin is really remarkable.
Remembers quite a bit of the large craters on Tethys:

Left: Melanthius
Right: Odysseus
---------------------------------------------------------------------------------------------------------------------------
Btw, 'Solar System Viewer' is now working with an updated Iapetus texture, finally...
Here five views from CASSINI:



Pretty improvement...

To lazy to check, is Iapetus in a proper orbit for saturnshine images?

And one from Saturn today:

Luckily sunshine outshines saturnshine today...
Due to its bounded orbit you can recognize the saturnshine side of Iapetus.

Bye.

[TritonAntares]

Hello,
another 9 images arrived from CASSINI.
Here one takeout:

Date: 2006/03/28
Distance: 2.188.203 km
Filters: CL1 and CL2

Bye.

[TritonAntares]

Hi,
another 10 far-distance images were taken from Iapetus.
Here one takeout:

Date: 2006/03/29
Distance: 2.103.960 km
Filters: CL1 and CL2

Bye.

[Rob Pinnegar]

This distant flyby could turn out to be pretty interesting. There look to be some interesting gradations in the colour of Cassini Regio in Iapetus south-leading quarter-sphere (demihemisphere?).

In a few of those distant shots TritonAntares has posted, you can see some of the bellyband mountains on the limb. Amazing how tall those things are.

[Michael Capobian...]

In a few of those distant shots TritonAntares has posted, you can see some of the bellyband mountains on the limb. Amazing how tall those things are.

I can't see the bellyband, but a few of these shots do show the Moat's central peak very clearly on the limb.

Michael

[Rob Pinnegar]

I can't see the bellyband, but a few of these shots do show the Moat's central peak very clearly on the limb.

Hmmm. You might be right about that one, Michael. I just sort of assumed that the peak on the limb was one of the bellyband peaks. It could very well be the Moat's central peak instead.

[TritonAntares]

In a few of those distant shots TritonAntares has posted, you can see some of the bellyband mountains on the limb. Amazing how tall those things are.

I can't see the bellyband, but a few of these shots do show the Moat's central peak very clearly on the limb.

Hmmm. You might be right about that one, Michael. I just sort of assumed that the peak on the limb was one of the bellyband peaks. It could very well be the Moat's central peak instead.

I always wondered about the trace of the bellyband in Iapetus eastern hemisphere.
It's so obvious in Steve Albers map:


I marked the supposed course of the bellyband in the above mentioned region south of the 'Snowman' of an enlarged map.
The central peak of 'Snowman A' is also encircled.


Compare with this image taken on Jan. 22, 2006, at a distance of approximately 1.3 million km:

You can easily see the enormous height of the Moat's central mountain.

But there is no hint due shadow casting for large mountains at the marked line of the supposed bellyband path,
but south of it seems to be a huge ridge (ellipse) casting a shadow to NNW like the inner crater rim of 'Snowman A'.
Therefore the bellyband in Iapetus eastern hemisphere must be quite low, if it exists at all
and this line in Steve Albers map is artifical there.


Bye.

[Michael Capobian...]

[quote name='TritonAntares' date='Apr 1 2006, 03:26 PM' post='48836']

But there is no hint due shadow casting for large mountains at the marked line of the supposed bellyband path,
but south of it seems to be a huge ridge (ellipse) casting a shadow to NNW like the inner crater rim of 'Snowman A'.
Therefore the bellyband in Iapetus eastern hemisphere must be quite low, if it exists at all and this line in Steve Albers map is artifical there.


Yes. Although there is a suggestive bright line there, it seems to be just a coincidence. The ridge you highlight appears to be part of an interesting crosshatching of ridges to the south, although it's very hard to make out what's going on at these low resolutions.

Michael

[TritonAntares]

Hello!

The ridge you highlight appears to be part of an interesting crosshatching of ridges to the south, although it's very hard to make out what's going on at these low resolutions.

You mean this mysterious doublecross structure:


What is this?
Tectonic rifts and ridges caused by the 'Snowman'?
Something connected with the equatorial ridge?
Or...?

Bye.

[scalbers]

Yes I agree the white line on the E edge of CR is a real albedo feature, though maybe a fortituous coincidence. The stereo imagery I had once shown didn't show any conclusive ridge there, though it might not completely be ruled out either. I am starting to reprocess some of the Saturnshine images in the hope of improving the noise reduction and resolution so that might help slightly. If I can add do this and find additional Saturnshine images from that encounter it could help both in the map and the stereo imaging.

The snowcapped peaks on the W side of CR do look more realistic as part of the bellyband.

All this to preface what are an interesting set of images coming in as we speak.

[Michael Capobian...]

Hello!
You mean this mysterious doublecross structure:


What is this?
Tectonic rifts and ridges caused by the 'Snowman'?
Something connected with the equatorial ridge?
Or...?

Tic Tac Toe board?

Michael

[ugordan]

You mean this mysterious doublecross structure:


What is this?
Tectonic rifts and ridges caused by the 'Snowman'?
Something connected with the equatorial ridge?
Or...?

This reminds me of the discussion on You-Know-What looking hill on Mars that was identified in Viking imagery years ago.
Seems that you're really trying to pull out too much information out of such a low-res view. For all we know, higher resolution might make this nothing like a double-cross.
Even now, that lower horizontal line you marked seems to end in a small crater on the right (you did extend it into the crater itself) , while the upper line follows its outer rim. The right vertical line thus outlines the interior wall of the crater. Human eye often likes to see patterns when there aren't any.

[TritonAntares]

This reminds me of the discussion on You-Know-What looking hill on Mars that was identified in Viking imagery years ago.
Seems that you're really trying to pull out too much information out of such a low-res view. For all we know, higher resolution might make this nothing like a double-cross.
Even now, that lower horizontal line you marked seems to end in a small crater on the right (you did extend it into the crater itself) , while the upper line follows its outer rim. The right vertical line thus outlines the interior wall of the crater. Human eye often likes to see patterns when there aren't any.

You're definitely right, these low resolution images lead to misinterpretations. The double-cross is for sure some
artifical structure, pretenced by the human eye.
After a 'second look' at the region I could recognize 3 craters (one of them you mentioned), the southern rim of 'Snowman A', the horizontal structure south of it and two vertical structures (parts of the double-cross):

Due to dark shadow casting the three structures should be ridges...

Bye.

[Decepticon]

Raws are up for April 1,2006

[TritonAntares]

Hi,
yes, the next 18 images arrived.
Here two takeouts:

Date: 2006/03/30
Distance: 2.000.937 km
Filters: CL1 and CL2


Date: 2006/04/01
Distance: 1.867.635 km
Filters: CL1 and CL2
Probably a large mountain visible at the right rim...

CASSINI is slowly getting closer...

Bye.

[Phil Stooke]

This is the latest view of Iapetus. It's a composite of six images from the latest batch, combined to reduce the JPEG artifacts and with a bit of selective contrast fiddling as well.

Phil

[Rob Pinnegar]

Hey, what's that white curve-shaped feature near Iapetus' south pole? Have we seen that thing before?

At first glance, and using a bit of imagination, it looks like it could be a partial arc of a basin rim -- and there are some other nearby arc-like features that look as if they are also part of the same structure. However, I can't tell whether my eyes are playing tricks on me, and filling in the rest of the pseudo-rim where I want it to be.

Hard to believe it could actually be a basin -- surely something that large couldn't have been overlooked. What else could it be? Another mountain range perhaps?

[ugordan]

Hey, what's that white curve-shaped feature near Iapetus' south pole? Have we seen that thing before?

I believe that's the south polar bright terrain, very overexposed here. We really haven't seen much of it in Cassini's images so far, but the hints in the New Years Eve flyby look like it's much brighter/cleaner ice than the (now well imaged) north pole.
This brightness dichotomy is stressing the ISS S/N ratio to the fullest, the team probably optimized for the Cassini Regio and that's why the south turned out so white. Contrast stretching might have played a role also.

[Decepticon]

At first glance it looked like a chain of craters?

[Phil Stooke]

Another view of Iapetus from the latest sequence. Again, it's a stack of six images, each one enlarged, contrast stretched and sharpened.

Phil

[TritonAntares]

Hey, what's that white curve-shaped feature near Iapetus' south pole? Have we seen that thing before?

At first glance, and using a bit of imagination, it looks like it could be a partial arc of a basin rim -- and there are some other nearby arc-like features that look as if they are also part of the same structure. However, I can't tell whether my eyes are playing tricks on me, and filling in the rest of the pseudo-rim where I want it to be.

Hard to believe it could actually be a basin -- surely something that large couldn't have been overlooked. What else could it be? Another mountain range perhaps?

This seems to be a former unknown structure, or say better a bad resolved one:
Here what is recognizable:

Left: part of Steve Albers map
Middle: Phils' stack of six images
Right: part of south polar projection

The white curve-shaped feature near Iapetus' south pole could be a crater chain or even some sort of graben.
Upcoming images will show this region in a better resolution.
Let's wait a few days...

Bye.

[TritonAntares]

So,
another 10 far-distance images arrived lately.
The takeout:

Date: 2006/04/02
Distance: 1.639.462 km
Filters: CL1 and CL2

Bye.

[TritonAntares]

Hello,
another 11 Iapetus far-distance images have been released lately.

Two takeouts:

Date: 2006/04/03
Distance: 1.496.620 km
Filters: CL1 and CL2


Date: 2006/04/04
Distance: 1.433.094 km
Filters: CL1 and CL2

Bye.

[Michael Capobian...]

Hello,
another 11 Iapetus far-distance images have been released lately.

Bye.

That ridge on the terminator continues to fascinate. It may be another one of those Iapetan anomalies. My prediction: this pass will give us an important new clue to the Iapetus mystery.

Michael

[Guest_BruceMoomaw_*]

Dennis Matson will have a paper at May's AGU meeting, "Forming Iapetus’ Equatorial Ridge". He's already stated elsewhere recently (can't quite remember where) that his studies show that, during Iapetus' early days when it was still being heated by its internal aluminum-26, and therefore stretched by its own as-yet fairly rapid rotation, the equatorial bulge is where its mantle's internal convective currents would have converged to upthrust the ridge.

[Phil Stooke]

The trick then becomes explaining the lack of ridges on other bodies.

Phil



Composite of two April 4 images plus a bit of magic.

[Michael Capobian...]

Actually, I was referring to the little curvilinear ridge visible near the terminator in the latest images. It could just be craters lined up or a basin rim remnant, but you can't tell for sure at this resolution.

As for the equatorial ridge, any theory would also have to explain why it isn't continuous all the way around Iapetus.

Michael

[Rob Pinnegar]

For what my opinion might be worth, the aluminum-26 hypothesis just can't cut it. Aluminum-26 has a half-life of less than a million years -- it would all have been gone pretty much right after Iapetus finished forming. How the heck could the equatorial ridge have survived, nearly intact, through four and a half billion years of crater formation, with no internal heat source to maintain it?

I guess the counterargument is that, if Iapetus were hot enough to start with, it would have taken a while to cool -- perhaps long enough to keep building the bellyband until after the major phase of crater formation. But is Iapetus big enough to have stayed liquid right through the late heavy bombardment? That's over 700 million years. And then there's Phil's point to consider, as well.

Unfortunately, although attacking this hypothesis is an easy thing to do, coming up with a better idea is a lot more difficult. The "Old Reliable" of internal energy sources -- tidal heating -- probably won't work here because Iapetus is way too far away from Saturn. That's too bad, because it's pretty close to being in a 5:1 resonance with Titan.

Maybe Iapetus' orbit was really, really elliptical a long time ago, and the slow process of circularization provided a long term source of tidal heating? That might explain why there are no other major moons past Hyperion. I'm grabbing at straws here, though... and have no idea if this process would provide even a fraction of the heat that would be required to keep internal circulation going.

This is a real mystery. The moon's overall shape and rugged appearance seem to suggest very rapid freezing. But the bellyband has to be younger than most of the craters which suggests long term internal activity. Strange.

[tasp]

A thought experiment:

Get a very precise cannon, one that can shoot bowling balls exactly 10 miles when aimed parallel to the surface.

Place the cannon on top of a hill 100 feet high.

Start firing. (you have an unlimited supply of bowling balls)

What happens?

First bowling ball zips out and lands 10 miles away. Second bowling ball hits first bowling ball.

Third, forth, etc.

Eventually, 10 miles away, we get a pile of bowling balls (in the thought experiment, the bowling balls don't break).

Keep firing.

Now what happens?

Kinetic energy of the incoming bowling balls eventually is insufficient to overcome the mass of the pile of already fired bowling balls. At this point, the bowling balls start accumulating on the cannon facing side of the bowling ball pile.

Keep firing.

As more and more bowling balls are fired at the pile, the pile 'grows' into the incoming stream of bowling balls. Fire long enough, and the pile becomes a ridge 'growing' upstream towards the cannon.

Let's change the model a little. Let's now fire the bowling balls at .00001% more than orbital velocity and change our altitude 1 foot higher for the cannon.

Now, the bowling balls make 1 orbit (neglecting air resistance) before an unspecified (at this point) drag force lowers the orbit of the bowling ball 1 foot and the bowling ball smacks the pile.

(note, we lower the cannon every time a bowling ball whizzes by)

Now what happens?

Bowling balls (after orbit decays 1 foot), still smack the pile, bowling balls still have insufficient energy to overcome the inertia of the existing pile, so the bowling balls keep accumulating on the 'upstream' side of the pile.

Let's change the model a little more now.

Let's put the cannon in a much higher orbit and fire zillions of cannon balls.

Cannon balls form a ring structure, very very similar to Saturns.

Cannon balls now have the opprotunity to interact with each other.

Lets's look at a particular cannon ball. As it orbits, it will from time to time, bump a cannon ball in a very slightly lower orbit. This will occur at a very low relative velocity. But it will happen often.

What is the result of the collision? A very small amount of energy will transfer (on average) from the lower bowling ball to the higher bowling ball. As a result, the lower bowling ball orbits a little lower. And the bowling ball above, wants to orbit a little higher.

But it will lightly bump its brethren in the next slightly higher orbit above, transfering energy to them, and itself falling back down to a slightly lower orbit.

This mechanism transfers energy from the low side of our bowling ball rings to the upper side.

The result of this is a very slow, but steady stream of bowling balls to ever lower orbits, at the expense of transfering energy to the upper side of the ring structure.

Eventually, we have a slow dribble of bowling balls smacking the highest point on the surface along their orbital ground track, and accumulating upstream all the while.


What of the bowling balls at the high side?

Possibilty exists that minor drag forces; air resistance if you grant a very small amount it, solar wind perhaps, light pressure, etc. saps enough energy from the system that you can emplace the entire ring structure on the surface without accumulating any material on the 'high side'.

What does our surfaced emplaced ring of bowling balls look like?

Given enough bowling balls, a long ridge!

As to Iapetus, replace 'bowling balls' with 'ice chuncks', and 'cannon' with orbited debris from oblique asteroid impact, and you can see how Iapetus got its ridge.

(time constraints now don't allow me to go into how you get an organized ring system from an impact, but a scientist named Laplace worked it out a couple of centuries ago)

[TritonAntares]

Hi,
the rest of the April 4th Iapetus image series - 80.000 km closer - is online.

Takeout of 9 shots - I did some gradation tuning:

Date: 2006/04/04
Distance: 1.352.785 km
Filters: CL1 and IR3
--------------------------------------------------------------------------------------------------------------------------------------------------------
The curvilinear ridge visible near the terminator in the latest images is obviously connected with a crater doublett,
one elongated crater north of the pair and a larger one south:

Thus the ridge could be sunlighted crater rims of those four.
The angle of incoming light is probably fooling us...
But there should be an interesting feature farther south (quadrangle) - maybe a huge mountain.
Looks like one of those mensae found on Io on this Iapetus polarmap.
I'm quite curious what CASSINI images will show there...

Bye.

[Michael Capobian...]

So we have exogenous and endogenous theories for the equatorial ridge as well.

What kind of observations will it take to sort this out? I guess if the ridge is eruptive, there should certainly be evidence of that in the close-ups in 2007. The white mountains in Western CR might look like cryovolcanoes, forex, or piles of welded cannon balls.

Michael

[Bob Shaw]

The flaw in the 'bowling ball' theory is that there's no chance of the plane of the orbit of the ring remaining fixed with relation to the surface of the moon, so the decaying ring particles wouldn't hit in a line but rather in a belly-band centered under the average orbital path (which migt well be sinusoidal). Saturn's system would have altogether too many and varied perturbations for the simplistic model to work!

Bob Shaw

[tasp]

Laplace worked out the scenario for getting all the materials in randomly inclined orbits over the equator long ago.

If you have a copy of The New Solar System, check out the chapter on planetary rings for a more complete description of the collapse of materials to the Laplacian plane.

When I saw that, I knew the equatorial ridge structure had to be the emplaced residue of ring system around Iapetus long ago.

Of all the major satellites in the solar system, Iapetus has the most isolated orbit from perturbing effects.

To anticipate another question, vaporization, the impacting debris on Iapetus would be traveling less than 1550 km/hr. Rather less if one feels Iapetus was rotating more rapidly in the past. (the weak tidal effects of distant Saturn braking Iapetus' primordial rotation would have been uniquely slow)

[Bob Shaw]

Of all the major satellites in the solar system, Iapetus has the most isolated orbit from perturbing effects.

To anticipate another question, vaporization, the impacting debris on Iapetus would be traveling less than 1550 km/hr. Rather less if one feels Iapetus was rotating more rapidly in the past. (the weak tidal effects of distant Saturn braking Iapetus' primordial rotation would have been uniquely slow)

It's the perturbations - the *many* perturbations - which are the fly in the ointment. Yes, rings do tend to become planar, and astonishingly self-organised, but in practice we just don't see them wherever there's anything other than one big(ish) body for the effect to work around.

If Iapetus were anything other than unique I might agree with you, but not this time!

Bob Shaw

[TritonAntares]

So we have exogenous and endogenous theories for the equatorial ridge as well.

What kind of observations will it take to sort this out? I guess if the ridge is eruptive, there should certainly be evidence of that in the close-ups in 2007. The white mountains in Western CR might look like cryovolcanoes, forex, or piles of welded cannon balls.

One question to answer should be:
What is older, the equatorial ridge or its surrunding/overlaying area, speak the craters?

Therefore I compared these two shots of the 'belly band':

Visible left is a large bassin in the western part of CR cut by the part of the ridge with the 'white peaks'.
Thus the crater must be older than them, even if its central peak doesn't coincide with the 'white peak' NW of it
and it is also lower. So you could guess the ridge there is fairly young, maybe eruptive....

In the right image another part of the ridge in central CR is shown. It seems to be quite old.
Lots of craters (red circles) crashed into it and disturbed its line.
The craters in the blue circles look somehow tilted, probably raised up by the ridge.
But due to bad resolution this is difficult to discern...

And don't forget there is no evidence for the ridge east of CR, only some uncertain albedo features.

Is the equatorial ridge powered by some longitudinal subsurfaced source or is there a gravitational cause from one direction?
The belts different heights and ages then could be explained by a longitudinal shift over a longterm period.

Bye.

[tasp]

Thanx for the picture, nice to see the ridge right side up.

I am having trouble imagining an internal process that can create a feature dead straight, aligned almost perfectly to the equator, that can operate for over 90 degrees of longitude . . .

Additionally, at the east end of this structure, is a conveniently huge circular impact depression (the one with the big landslide) that is miles deep. There seems to be no sign of any defect or discontinuity in the exposed crustal materials at that location.

Cratering of the adjacent plains seems similar to the cratering on the ridge to my untrained eye. Ridge is ancient.

Craters on such an elevated structure might have 'strange' morphologies compared to their analogs on the plains.

I also note, the steepness of the sides of the ridge. Plausibly the angle of repose for solid materials placed from above, rather than the expected slopes of a presumably runny iceyCO2/ammonia slurry?

The symmetry of the diverging attendant ramps is also striking. An internal process doing that . . . .?

Perhaps the 'attendants' reflect precession of the axis of rotation of Iapetus during the final stages of emplacement. Or similarly, slightly inclined structures in the outer portion of the Iapetan ring system.

I claim no special training in gravitional perturbation theory, but about the only thing I can imagine external perturbations doing to a potential ring system on lonely Iapetus, is to slightly speed up the momentum transfer process that places the materials onto the surface.

[Guest_BruceMoomaw_*]

I am having trouble imagining an internal process that can create a feature dead straight, aligned almost perfectly to the equator, that can operate for over 90 degrees of longitude . . .

The idea of Matson et al is that the centrifugal force of Iapetus' initial fairly fast spin, while its interior was still warm and plastic, created the major oblate bulge one sees in it, and in the process created convection loops of warm ice on either side of the equator that "folded" the cooler surface ice into a nice neat ridge at the equator (which is what they claim their calculations show would happen in such a situation). Then -- at about the time Iapetus' spin had been tidally slowed to once every 17 hours -- the Al-26-generated heat died out and Iapetus "froze" with the degree of oblate shape it had at that point; and during the eons since then, Saturn's tides have finished braking it into completely synchronous rotation and dragged its now-solidified oblate bulge into line with the planet. More on this shortly.

[Guest_BruceMoomaw_*]

The best summaries of the views of Matson, Jonathan Lunine and Julie Castillo are from the two 2005 AGU meetings:
http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P14A-03"

http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P21F-02"

As for WHY they believe this, see the second paper: "We revisited Iapetus' dynamical evolution models in order to understand under which conditions the observed non-hydrostatic shape of this satellite (corresponding to a past 17-hr geoid) became frozen and was preserved until the present. This study highlights the need of extra sources of energy not considered in previous thermal evolution models for the Saturnian satellites. Thermal evolution models driven by the decay of long-lived radiogenic species do not produce a temperature high enough for a body such as Iapetus, composed only of 20% silicate by mass and 3.561 10e6 km distant from its primary, to despin over the age of the Solar System. Different approaches were considered to increase the internal temperature: alteration of the surface properties to limit heat loss (greenhousing, low emissivity, insulating layer), impact heating, and enrichment in long-lived radiogenic species. None of these approaches can account for the despinning, except enrichment in long-lived radiogenic species. However that option cannot produce models that preserve the 17-h geoid. We demonstrate that short-lived radiogenic species, especially 26Al, as found in the Calcium-Aluminum-Inclusions (CAIs) provide conditions suitable for models that match the observational constraints. The relatively short half-life of 26Al allows the constraint of Iapetus' formation time with high accuracy: 1.0+/-0.2 to 1.6+/-0.4 My after the production of CAIs. This new result provides a strong constraint on the formation of Saturn. Based on current values for the absolute formation time of the CAIs, Saturn's age is estimate as 4.566 5 By."

That is: Iapetus -- given its great distance from Saturn -- had to be quite warm for a while in order to be plastic enough for the friction from Saturn's tides to have slowed it down to synchronous rotation by now. But if it was warm enough for that because it was unusually rich in the long-lived radioisotopes (U, Th, K-40), it would have stayed soft long enough to lose its current shape, which seems to be the shape it would have had from centrifugal force as a sphere spinning as fast as once every 17 hours. So it had to be very warm and soft for a very short period very early on, to tidally decelerate very quickly down to a rotation rate of once every 17 hours -- and then it had to suddenly lose its internal heat and freeze at that point, after which very slow continuing tidal dissipation despite the fact that it was now solidified would be adequate, over almost the entire lifetime of the Solar System, to slow it down further to its current synchronous 79-day rotation by now. And the only heat source that could do that sort of thing would be an initial abundance of intense but short-lived radioisotopes in it, with the only plausible candidate being Al-26.

[nprev]

Hmm. Almost makes you wonder if Enceladus was similarly enriched in radioactives, doesn't it? Dissapating fossil heat might be a bit harder to do deep in the gravity well of Saturn with Dione & Tethys adding their own increments of tidal heating.

Odd things happening out there...

[Guest_BruceMoomaw_*]

Actually, Castillo et al are thinking of precisely that -- especially since Enceladus' rock-ice ratio is considerably higher than that for any of the other icy moons:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2200.pdf

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2219.pdf

Their belief is that this is exactly what "jump-started" Enceladus' heating -- which later, after the radioisotopes had decayed, was able to sustain itself due to the amount of tidal friction acting on Enceladus' internal magma (although such tidal-frictional heating could never have started up in the first place in an Enceladus that was initially cold and thus rigid).

[TritonAntares]

The idea of Matson et al is that the centrifugal force of Iapetus' initial fairly fast spin, while its interior was still warm and plastic, created the major oblate bulge one sees in it, and in the process created convection loops of warm ice on either side of the equator that "folded" the cooler surface ice into a nice neat ridge at the equator (which is what they claim their calculations show would happen in such a situation). Then -- at about the time Iapetus' spin had been tidally slowed to once every 17 hours -- the Al-26-generated heat died out and Iapetus "froze" with the degree of oblate shape it had at that point; and during the eons since then, Saturn's tides have finished braking it into completely synchronous rotation and dragged its now-solidified oblate bulge into line with the planet. More on this shortly.

Interesting point,
raises the question why Iapetus' spin degraded from say once a few hours to now about 80 days?
Couldn't Iapetus been capatured by Saturn?

It has a 15° tilted orbit far out of the other saturnian satellites, the most distant out of all the larger solar systems moons.
As a lonely object (centaur, KBO, left planetesimal from solar systems early ages...) it would have had a rotation period of say a few hours to a few days, for sure vastly shorter than today.
Once being captured, Iapetus was forced in its locked orbit, first its cool crust and than its warmer pseudoliquid interior had been tidally slowed.
For some time this inner part could even have been heated up by shear & relaxation effects - and perhaps the Al-26 decay.
In this period the ridge was created. The longitudinal distribution of the belt could be caused by some tidal effect,
when Iapetus was in a transition period between faster spinning and locked rotation
and the interior was still warm enough to transport material in this part of the crust.

Paradoxically the ridge is now positioned on the anti-saturn hemisphere, a position not to be expected.
Maybe Iapetus cooled down to todays conditions before synchronous rotation was achieved.

Not to forget is the strange triaxial ellipsoid figure (radii 732x726x722 km) of Iapetus...

Bye.

[TritonAntares]

So,
one lonely Iapetus images was released lately:

Date: 2006/04/06
Distance: 1.140.455 km
Filters: CL1 and CL2

Bye.

[tasp]

My thoughts on 'the good old days' on Iapetus seem to be at variance to the mainstream now.

Iapetus, while in a somewhat tilted orbit, has a comfortably low eccentricity, I never felt Iapetus formed anywhere else.

Considering the ~80 day period around Saturn, it seemed that Iapetus' accretion phase would have been quite leisurely, it just taking so much longer to 'sweep up all the fixins'.

In view of a long accretion process, we might expect Iapetus to have had time to radiate the impact derived heating and avoiding, or greatly minimizing a globally molten phase. This might explain the 'lumpy limb' we see in various areas in the Cassini pictures (not talking about the equatorial ridge here). Iapetus having had a rigid crust earlier in it's history than most (all?) other moons and able to retain greater deviations from sphericity from impact damage.

Having a more rigid crust earlier in the game than other moons allows preservation of features perhaps not seen on other objects, like the equatorial ridge structure.

Iapetus shares a trait with several other moons of Saturn (although I am not claiming any special significance for this) in that it is close (but not in) to a strong resonance of another satellite. Weird (to me) that Io, Europa, and Ganymede are in a mutual resonance, and other than scale, the highly similar Uranian satellites are not. And then we have Saturn, resonance features all across the rings, and moons (except for Hyperion, probably a special case) only close to resonances.


The synchronous rotation findings are certainly a surprise.

Iapetus remains a 'weird wee beastie'.

[angel1801]

I checked the raw images just a few minutes ago. Images ranging from about 922,000 km to about 1,050,000 km are available now.

[Steve G]

My thoughts on 'the good old days' on Iapetus seem to be at variance to the mainstream now.

Iapetus, while in a somewhat tilted orbit, has a comfortably low eccentricity, I never felt Iapetus formed anywhere else.

Considering the ~80 day period around Saturn, it seemed that Iapetus' accretion phase would have been quite leisurely, it just taking so much longer to 'sweep up all the fixins'.

In view of a long accretion process, we might expect Iapetus to have had time to radiate the impact derived heating and avoiding, or greatly minimizing a globally molten phase. This might explain the 'lumpy limb' we see in various areas in the Cassini pictures (not talking about the equatorial ridge here). Iapetus having had a rigid crust earlier in it's history than most (all?) other moons and able to retain greater deviations from sphericity from impact damage.

Having a more rigid crust earlier in the game than other moons allows preservation of features perhaps not seen on other objects, like the equatorial ridge structure.

Iapetus shares a trait with several other moons of Saturn (although I am not claiming any special significance for this) in that it is close (but not in) to a strong resonance of another satellite. Weird (to me) that Io, Europa, and Ganymede are in a mutual resonance, and other than scale, the highly similar Uranian satellites are not. And then we have Saturn, resonance features all across the rings, and moons (except for Hyperion, probably a special case) only close to resonances.
The synchronous rotation findings are certainly a surprise.

Iapetus remains a 'weird wee beastie'.

What effect would have Saturn's protoplanet heat had on the inner moons compared to Iapetus? If Saturn was radiating heat to the inner system, the icy moons would have had a warmer crust than Iapetus. Perhaps Ithica Chasma may have resulted from a warmer environment until Saturn itself cooled down?

[TritonAntares]

Hi,
this time some more Iapetus images (altogether 29);
Here three takeouts:

Date: 2006/04/05
Distance: 1.207.215 km
Filters: CL1 and CL2


Date: 2006/04/06
Distance: 1.062.356 km
Filters: CL1 and CL2


Date: 2006/04/07
Distance: 923.304 km
Filters: CL1 and CL2

Some details of the latest image (2,75 x enlarged):

3 certainly identified craters are marked.
The mountain (quadrangle) is casting a large shadow,
it must be quite high...
As mentioned before, the curvilinear ridge seems more and more connected with 3 sunlighted crater rims...

Bye.

[TritonAntares]

Hi again,
after a second look at the latest Iapetus image I believe to have recognized 2 further large ancient bassins in central CR:

The blue marked one was mentioned a few months ago in this forum,
but the green marked was - as far as I know - never mentioned before.
The central peaks are inside the gray rectangles.
Maybe someone can do some contrast enhencement...

Bye.

[Decepticon]

Wow, I didn't notice the second basin!

[alan]

I brightened the image The right side of green 'basin' looks more like a few craters lined up, the left side the outer rim of the blue basin.

[angel1801]

I checked the raw images just a few minutes ago. Images ranging from about 922,000 km to about 1,050,000 km are available now.

Just checked again. Images are now only 822,000 km from Iapetus now.

[TritonAntares]

Just checked again. Images are now only 822,000 km from Iapetus now.

So,
seven more Iapetus images came in only a few hours later.
As I heard, there will be at least 2 transmissions per day from now on.

The Takeout:

Date: 2006/04/08
Distance: 865.497 km
Filters: CL1 and IR3

I brightened the image. The right side of green 'basin' looks more like a few craters lined up,
the left side the outer rim of the blue basin.

Odd coincidence...

Bye.

[Phil Stooke]

Here is the latest view... two images stacked. I wouldn't rule out the possibility of another basin, but the important thing is to check back through images from all the other flybys to see it in different viewing and illumination conditions.

Phil

[Decepticon]

Phil what program did you use to stack the images?

[Phil Stooke]

I do everything in Photoshop.

Phil

[Decepticon]

Here is my best atemped.

[Phil Stooke]

Nice. What I did differently was to make feathered selections across the darker area and brighten them without over-brightening the lighter areas. Then repeating that for the near-terminator area. The high pass filter does this as well but produces other artifacts along edges.

Phil

[Rob Pinnegar]

A stereo pair might help determine whether that "basin" is really a basin. I know it's not easy to do that when Cassini is approaching Iapetus (especially this close to the terminator), but it's worth mentioning, at least.

[TritonAntares]

Nice work,
if you look at the smaller attached version there seems to be a circular structure resembling a large bassin,
but the larger image doesn't confirm this impression.
Probably this bassin is highly degraded by impacts and for sure older than the one next to it.

The mountainous region near the southpole gets more and more interesting while coming into sunlight.
Are there also two craters involved in this structure?
----------------------------------------------------------------------------------------------------------------------
EDIT:
(1)
Tilmann Denk - he is working on Iapetus ISS-data at FU-Berlin - confirmed me the existence of a second large southern bassin lately.
It has long been supposed in this image from July 2004 (green circle):

In one of the incoming image series the 2 mid-sized craters (blue rectangle) will certainly appear.

(2)
Tilmann also informed me about the prior mentioned mountain at the right rim of this april 1st image:

It is most likely placed in the short part of the equatorial ridge east of the known giant bassin in eastern CR
(with the landslide) and another even more eastern bassin.
This second before unknown bassin and the mountain showed up in a digital terrain model!

Bye.

[Rob Pinnegar]

I wouldn't mind seeing some of those "digital terrain models" of Iapetus. A few months ago Jason mentioned that there was at least one really big basin in Cassini Regio, that is degraded so much that it can only be seen in topography maps.

There are about four big basins on Iapetus that are fairly easy to see. This new one really isn't very visible, and there are undoubtedly others besides the one Jason mentioned that we can't see very easily either. It would be very interesting to see how many there really are.

I guess probably the reason we haven't seen topography maps yet is that they are part of somebody's research. So if we're lucky they will pop up in a conference talk extended abstract or something along those lines. Till then we'll have to be patient.

[angel1801]

Just checked again. Images are now only 822,000 km from Iapetus now.

I've just checked again. Images are available for distances as low as 695,000 km. There even is a
"saturn shine" shot as well (the first of this distant Iapetus encounter!)

[ugordan]

There even is a "saturn shine" shot as well (the first of this distant Iapetus encounter!)

I assume you're referring to this image. That's not saturnshine, it's only Iapetus' disk heavily overexposed. AFAIK, the geometry is such that the saturnshine lit portion of Iapetus is on the far side of the visible disc. Furthermore, Saturn's disc itself is a very thin crescent at this point in Iapetus' orbit so any saturnshine is feeble, practically non-existent.

[Rob Pinnegar]

Yes, that's right. Remember that Saturnshine can only illuminate the side of Iapetus that faces Saturn! Unfortunately, the part of Iapetus that is dark in the new images is the side that faces away from the planet. This means that it isn't getting any light at all, except for starlight, and that's nowhere near enough for imaging purposes.

This is too bad, because if we could see the "dark part" of Iapetus in the new images, we'd be able to see the huge Roncevaux Terra basin which is over 400 km across. Such is life.

[angel1801]

I assume you're referring to this image. That's not saturnshine, it's only Iapetus' disk heavily overexposed. AFAIK, the geometry is such that the saturnshine lit portion of Iapetus is on the far side of the visible disc. Furthermore, Saturn's disc itself is a very thin crescent at this point in Iapetus' orbit so any saturnshine is feeble, practically non-existent.

I always assumed any way over-exposed shot of any moon (especially with Iapetus) of Saturn is
always Saturnshine (or an attempt to do it!) . I now know better.

[TritonAntares]

So,
CASSINI broadcasted 21 more Iapetus images.

Four Takeouts:

Date: 2006/04/09
Distance: 777.087 km
Filters: CL1 and CL2


Date: 2006/04/09
Distance: 722.712 km
Filters: CL1 and CL2


Date: 2006/04/09
Distance: 711.286 km
Filters: CL1 and CL2
The mentioned crater pair is visible at the terminator.
Look at the disturbed figure of this moon...


Date: 2006/04/09
Distance: 699.281 km
Filters: CL1 and CL2
The second southern bassin is getting more and more prominent.
----------------------------------------------------------------------------------------------------------

I've just checked again. Images are available for distances as low as 695,000 km. There even is a
"saturn shine" shot as well (the first of this distant Iapetus encounter!)

Btw, the region for possible saturnshine again:



Bye.

[Michael Capobian...]

If the northern "blue" basin rim intersects the bellyband, it should be very easy to determine which is older. Looks to me like the bellyband may postdate the basin, which is another thing any theory of its formation would have to explain.

Michael

[TritonAntares]

If the northern "blue" basin rim intersects the bellyband, it should be very easy to determine which is older. Looks to me like the bellyband may postdate the basin, which is another thing any theory of its formation would have to explain.

Difficult to say where the rims of both bassins are...
The northern one is bounded by large eroded craters, the southern nearly invisible on this map.
The northern bassin is surely older than the craters and they seem to be older than the equatorial ridge,
but some closer look should be taken there...

...the prior mentioned mountain at the right rim of this april 1st image:

It is most likely placed in the short part of the equatorial ridge east of the known giant bassin in eastern CR
(with the landslide) and another even more eastern bassin.
This second before unknown bassin and the mountain showed up in a digital terrain model!

I also tried to locate this 'far eastern' bassin in Steve's map,
but there is only a barely detectable curved structure - eastern rim? - visible (green doted line) ....

Possible positions of the 'mountain at the right rim' are marked red, the 'belly band' is shown as black line
and the known eastern CR-bassin in the blue circle.
Who has any idea?

Bye.

[Decepticon]

Another try at it.

Tricky to bring detail out without over exposing the lighter areas.

[Guest_BruceMoomaw_*]

If the northern "blue" basin rim intersects the bellyband, it should be very easy to determine which is older. Looks to me like the bellyband may postdate the basin, which is another thing any theory of its formation would have to explain.

Michael

Note Matson's new AGU abstract ( http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P33A-04" ): "Crater counting indicates that the ridge is as old as its surroundings (Giese et al. BAAS 37, 2005). This indicates the formation of this feature early in Iapetus' history. Its location at the equator might hold the key to its origin."

[Phil Stooke]

The latest Iapetus view... composite of two images again.

Phil

[Michael Capobian...]

Note Matson's new AGU abstract ( http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P33A-04" ): "Crater counting indicates that the ridge is as old as its surroundings (Giese et al. BAAS 37, 2005). This indicates the formation of this feature early in Iapetus' history. Its location at the equator might hold the key to its origin."

The ridge is certainly older than many of the small craters superposed on it, and it would probably support Matson's theory if it were the oldest feature there. If the ridge is younger than the northern basin and formed at a time when Iapetus's crust was very plastic, there should be evidence of that in the basin as well.

Michael

[Big_Gazza]

Seems odd that most of the Iapetus images seem to be at a near-constant exposure time. I would have expected images to be taken at differing exposure times to suit the differing surface reflectivities, short exposure for the high(er)-albedo southern region, and long exposures to bring out details in Cassini Regio.

Cheers,

Gary