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Posted by: TritonAntares Mar 14 2006, 01:04 PM

First of all, again the two existing encounter animations:
http://www.mmedia.is/bjj/misc/css_stuff/misc/iapetus_jan2006.avi
http://www.greuti.ch/cassini/japetus_april.avi

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.

Posted by: TritonAntares Mar 17 2006, 10:28 AM

QUOTE (TritonAntares @ Mar 14 2006, 02:04 PM)

Posted by: angel1801 Mar 17 2006, 01:16 PM

QUOTE (TritonAntares @ Mar 17 2006, 07:58 PM)

I've forgotten a third one:
http://www.unmannedspaceflight.com/index.php?act=Attach&type=post&id=3841

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.

Posted by: scalbers Mar 17 2006, 07:24 PM

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/iapetus/iapetus_apr06_1.jpg

http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_apr06_2.jpg

Posted by: angel1801 Mar 18 2006, 12:43 PM

QUOTE (scalbers @ Mar 18 2006, 04:54 AM)

Posted by: helvick Mar 18 2006, 02:29 PM

QUOTE (angel1801 @ Mar 18 2006, 12:43 PM)

Posted by: scalbers Mar 18 2006, 02:54 PM

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.

Posted by: Phil Stooke Mar 18 2006, 06:27 PM

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

Posted by: um3k Mar 19 2006, 04:51 AM

QUOTE (Phil Stooke @ Mar 18 2006, 01:27 PM)

Posted by: edstrick Mar 19 2006, 12:24 PM

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.

Posted by: TritonAntares Mar 19 2006, 06:59 PM

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:

Posted by: scalbers Mar 20 2006, 08:31 PM

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

Posted by: TritonAntares Mar 20 2006, 11:03 PM

QUOTE (um3k @ Mar 19 2006, 05:51 AM)

Posted by: tedstryk Mar 22 2006, 09:27 PM

QUOTE (TritonAntares @ Mar 19 2006, 06:59 PM)

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

Posted by: TritonAntares Mar 23 2006, 10:33 AM

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.

Posted by: Decepticon Mar 23 2006, 01:55 PM

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

Posted by: ugordan Mar 23 2006, 02:03 PM

QUOTE (Decepticon @ Mar 23 2006, 02:55 PM)

Posted by: TritonAntares Mar 24 2006, 11:25 AM

QUOTE (tedstryk @ Mar 22 2006, 10:27 PM)

Posted by: tedstryk Mar 24 2006, 02:13 PM

QUOTE (TritonAntares @ Mar 24 2006, 11:25 AM)

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.

Posted by: scalbers Mar 24 2006, 06:56 PM

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?

Posted by: TritonAntares Mar 24 2006, 10:01 PM

QUOTE (scalbers @ Mar 24 2006, 07:56 PM)

Posted by: Decepticon Mar 27 2006, 01:09 PM

Images stared coming in... http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS19/N00056025.jpg

Posted by: TritonAntares Mar 27 2006, 02:05 PM

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

Posted by: TritonAntares Mar 28 2006, 06:24 PM

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

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

Bye.

Posted by: TritonAntares Mar 29 2006, 11:26 AM

Hi,
http://www.geoinf.fu-berlin.de/projekte/cassini/cassini_gal_iap.php a Iapetus picture gallery from the German FU-Berlin.
Some images were unpublised until now.
Bye.

Posted by: Decepticon Mar 30 2006, 01:19 AM

Those night side images are just breath taking!

Posted by: BruceMoomaw Mar 30 2006, 02:41 AM

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

Posted by: tedstryk Mar 30 2006, 03:12 AM

QUOTE (BruceMoomaw @ Mar 30 2006, 02:41 AM)

Posted by: mchan Mar 30 2006, 04:21 AM

QUOTE (BruceMoomaw @ Mar 29 2006, 06:41 PM)

Posted by: TritonAntares Mar 30 2006, 07:54 AM

Hi,
ever seen this series?

Posted by: TritonAntares Mar 30 2006, 06:15 PM

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

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

Bye.

Posted by: TritonAntares Apr 1 2006, 10:02 AM

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.

Posted by: Rob Pinnegar Apr 1 2006, 04:20 PM

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.

Posted by: Michael Capobianco Apr 1 2006, 05:41 PM

QUOTE (Rob Pinnegar @ Apr 1 2006, 11:20 AM)

Posted by: Rob Pinnegar Apr 1 2006, 06:07 PM

QUOTE (Michael Capobianco @ Apr 1 2006, 10:41 AM)

Posted by: TritonAntares Apr 1 2006, 08:26 PM

QUOTE (Rob Pinnegar @ Apr 1 2006, 06:20 PM)

QUOTE (Michael Capobianco @ Apr 1 2006, 07:41 PM)

QUOTE (Rob Pinnegar @ Apr 1 2006, 08:07 PM)

Posted by: Michael Capobianco Apr 1 2006, 08:50 PM

[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

Posted by: TritonAntares Apr 1 2006, 10:48 PM

Hello!

Posted by: scalbers Apr 2 2006, 12:51 AM

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.

Posted by: Michael Capobianco Apr 2 2006, 03:18 AM

QUOTE (TritonAntares @ Apr 1 2006, 05:48 PM)

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...?

Posted by: ugordan Apr 2 2006, 10:34 AM

QUOTE (TritonAntares @ Apr 1 2006, 11:48 PM)

You mean this mysterious doublecross structure:


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

Posted by: TritonAntares Apr 2 2006, 01:15 PM

QUOTE (ugordan @ Apr 2 2006, 12:34 PM)

Posted by: Decepticon Apr 2 2006, 02:07 PM

Raws are up for April 1,2006

Posted by: TritonAntares Apr 2 2006, 06:56 PM

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.

Posted by: Phil Stooke Apr 3 2006, 02:08 AM

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

Posted by: Rob Pinnegar Apr 3 2006, 05:23 AM

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?

Posted by: ugordan Apr 3 2006, 07:17 AM

QUOTE (Rob Pinnegar @ Apr 3 2006, 06:23 AM)

Posted by: Decepticon Apr 3 2006, 12:32 PM

At first glance it looked like a chain of craters?

Posted by: Phil Stooke Apr 3 2006, 01:32 PM

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

Phil

Posted by: TritonAntares Apr 3 2006, 02:21 PM

QUOTE (Rob Pinnegar @ Apr 3 2006, 07:23 AM)

Posted by: TritonAntares Apr 3 2006, 03:53 PM

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

Posted by: TritonAntares Apr 5 2006, 05:05 PM

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

Two takeouts:

Posted by: Michael Capobianco Apr 5 2006, 06:16 PM

QUOTE (TritonAntares @ Apr 5 2006, 01:05 PM)

Posted by: BruceMoomaw Apr 6 2006, 12:27 AM

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.

Posted by: Phil Stooke Apr 6 2006, 01:24 AM

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

Phil

Posted by: Michael Capobianco Apr 6 2006, 04:03 AM

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

Posted by: Rob Pinnegar Apr 6 2006, 03:02 PM

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.

Posted by: tasp Apr 6 2006, 03:03 PM

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)

Posted by: TritonAntares Apr 6 2006, 03:13 PM

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:

Posted by: Michael Capobianco Apr 6 2006, 03:19 PM

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

Posted by: Bob Shaw Apr 6 2006, 03:34 PM

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

Posted by: tasp Apr 6 2006, 05:08 PM

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)

Posted by: Bob Shaw Apr 6 2006, 05:47 PM

QUOTE (tasp @ Apr 6 2006, 06:08 PM)

Posted by: TritonAntares Apr 6 2006, 07:54 PM

QUOTE (Michael Capobianco @ Apr 6 2006, 05:19 PM)

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.

Posted by: tasp Apr 6 2006, 11:59 PM

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.

Posted by: BruceMoomaw Apr 7 2006, 01:34 AM

QUOTE (tasp @ Apr 6 2006, 11:59 PM)

Posted by: BruceMoomaw Apr 7 2006, 03:39 AM

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?&listenv=table&multiple=1&range=1&directget=1&application=sm05&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Fsm05%2Fsm05&maxhits=200&="P14A-03"

http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm05&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm05%2Ffm05&maxhits=200&="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.

Posted by: nprev Apr 7 2006, 05:32 AM

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...

Posted by: BruceMoomaw Apr 7 2006, 05:50 AM

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).

Posted by: TritonAntares Apr 7 2006, 10:21 AM

QUOTE (BruceMoomaw @ Apr 7 2006, 03:34 AM)

Posted by: TritonAntares Apr 7 2006, 01:45 PM

So,
one lonely Iapetus images was released lately:

Posted by: tasp Apr 7 2006, 02:39 PM

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'.

Posted by: angel1801 Apr 8 2006, 01:56 PM

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.

Posted by: Steve G Apr 8 2006, 05:48 PM

QUOTE (tasp @ Apr 7 2006, 07:39 AM)

Posted by: TritonAntares Apr 8 2006, 08:13 PM

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

Posted by: TritonAntares Apr 8 2006, 09:14 PM

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

Posted by: Decepticon Apr 8 2006, 10:36 PM

Wow, I didn't notice the second basin!

Posted by: alan Apr 8 2006, 11:55 PM

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.

Posted by: angel1801 Apr 9 2006, 05:11 AM

QUOTE (angel1801 @ Apr 8 2006, 11:26 PM)

Posted by: TritonAntares Apr 9 2006, 11:15 AM

QUOTE (angel1801 @ Apr 9 2006, 07:11 AM)

Posted by: Phil Stooke Apr 9 2006, 02:41 PM

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

Posted by: Decepticon Apr 9 2006, 03:40 PM

Phil what program did you use to stack the images?

Posted by: Phil Stooke Apr 9 2006, 03:45 PM

I do everything in Photoshop.

Phil

Posted by: Decepticon Apr 9 2006, 04:13 PM

Here is my best atemped.

Posted by: Phil Stooke Apr 9 2006, 04:25 PM

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

Posted by: Rob Pinnegar Apr 9 2006, 04:37 PM

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.

Posted by: TritonAntares Apr 9 2006, 05:28 PM

QUOTE (Decepticon @ Apr 9 2006, 06:13 PM)

Posted by: Rob Pinnegar Apr 10 2006, 04:38 AM

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.

Posted by: angel1801 Apr 10 2006, 12:31 PM

QUOTE (angel1801 @ Apr 9 2006, 02:41 PM)

Posted by: ugordan Apr 10 2006, 12:38 PM

QUOTE (angel1801 @ Apr 10 2006, 01:31 PM)

Posted by: Rob Pinnegar Apr 10 2006, 01:22 PM

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.

Posted by: angel1801 Apr 10 2006, 01:37 PM

QUOTE (ugordan @ Apr 10 2006, 10:08 PM)

Posted by: TritonAntares Apr 10 2006, 02:41 PM

So,
CASSINI broadcasted 21 more Iapetus images.

Four Takeouts:

QUOTE (angel1801 @ Apr 10 2006, 02:31 PM)

Posted by: Michael Capobianco Apr 10 2006, 03:41 PM

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

Posted by: TritonAntares Apr 10 2006, 06:46 PM

QUOTE (Michael Capobianco @ Apr 10 2006, 05:41 PM)

...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!

Posted by: Decepticon Apr 11 2006, 02:03 AM

Another try at it.

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

Posted by: BruceMoomaw Apr 11 2006, 02:21 AM

QUOTE (Michael Capobianco @ Apr 10 2006, 03:41 PM)

Posted by: Phil Stooke Apr 11 2006, 03:16 AM

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

Phil

Posted by: Michael Capobianco Apr 11 2006, 04:05 AM

QUOTE (BruceMoomaw @ Apr 10 2006, 10:21 PM)

Posted by: Big_Gazza Apr 11 2006, 09:52 AM

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

Posted by: ugordan Apr 11 2006, 09:57 AM

There probably have been different exposure times used, but you can't deduce that from the raw images as they are automatically histogram-stretched before being posted on the net as JPEGs. As a result, most of the frames tend to have the same brightness.
The stretching makes it impossible to figure out the real color of the objects, one can only map color differences.

Posted by: TritonAntares Apr 11 2006, 01:54 PM

Hi,
next Iapetus-series is released, altogether 9 raw-images.

Here a triplett - original, enhenced by gradation, and 2 negatives for dark/bright hemisphere;
the overexposed southern disk rim is really difficult to manage...

Posted by: volcanopele Apr 11 2006, 07:24 PM

QUOTE (Big_Gazza @ Apr 11 2006, 02:52 AM)

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.

Posted by: Phil Stooke Apr 12 2006, 01:13 PM

the latest batch of Iapetus images... I stacked four frames - little effect at the south pole, but it's important for reducing the JPEG artifacts in the dark area.

Phil

Posted by: tasp Apr 12 2006, 02:43 PM

QUOTE (Michael Capobianco @ Apr 10 2006, 11:05 PM)

Posted by: TritonAntares Apr 12 2006, 07:18 PM

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

Two Takeouts:

Posted by: scalbers Apr 12 2006, 07:57 PM

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

Posted by: Phil Stooke Apr 12 2006, 08:27 PM

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

Phil

Posted by: TritonAntares Apr 12 2006, 10:33 PM

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

Posted by: dilo Apr 13 2006, 05:10 AM

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

Posted by: TritonAntares Apr 13 2006, 10:28 AM

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

Posted by: TritonAntares Apr 13 2006, 12:59 PM

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

Here three takeouts:

Posted by: Decepticon Apr 13 2006, 01:15 PM

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

Posted by: TritonAntares Apr 13 2006, 01:39 PM

QUOTE (Decepticon @ Apr 13 2006, 03:15 PM)

Posted by: Rob Pinnegar Apr 13 2006, 03:06 PM

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.

Posted by: Michael Capobianco Apr 13 2006, 04:10 PM

QUOTE (Rob Pinnegar @ Apr 13 2006, 11:06 AM)

Posted by: JRehling Apr 13 2006, 07:35 PM

QUOTE (TritonAntares @ Apr 13 2006, 05:59 AM)

Posted by: hendric Apr 13 2006, 09:04 PM

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.

Posted by: Rob Pinnegar Apr 13 2006, 10:10 PM

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".

Posted by: angel1801 Apr 14 2006, 08:50 AM

QUOTE (Rob Pinnegar @ Apr 14 2006, 12:36 AM)

Posted by: ugordan Apr 14 2006, 09:32 AM

QUOTE (angel1801 @ Apr 14 2006, 09:50 AM)

Posted by: angel1801 Apr 14 2006, 12:41 PM

QUOTE (angel1801 @ Apr 14 2006, 06:20 PM)

Posted by: TritonAntares Apr 14 2006, 01:27 PM

So,
next 9 Iapetus-images were released.

Three Takeouts:

Posted by: Bob Shaw Apr 14 2006, 03:07 PM

Regarding the 'rays', the large dim circular feature (sort of anti-vignetting) makes me pretty sure it's internal reflection/refraction.

Bob Shaw

Posted by: TritonAntares Apr 14 2006, 05:53 PM

Hi,
I tried to identify some topografic southpole structures in the april 12th images:

Posted by: scalbers Apr 14 2006, 11:31 PM

Greetings,

Nice to see all the updates and image analysis. From what I can gather on Mark Showalter's web site, the south pole actually has a solar elevation of about 3 degrees right now so it shouldn't really be in too deep of a shadow. I'm beginning to think my map will (at some point) need adjustment by a couple of degrees with some of the features marked above by Triton Antares moved closer to the pole to get them navigated right. We should also enjoy the current flyby in the sense that the 2007 flyby will have the south pole lying in a deeper shadow.

I'm currently working with some of the more recent images so I hope to post a new map when I get a clean result that is better than what was previously posted.

Posted by: tasp Apr 15 2006, 04:04 AM

If I could field a question:

Does the ~14 degree tilt of the Iapetan orbit around Saturn make the plane of the Iapetan orbit more parallel to the ecliptic or less?

Does this parameter change over time? Would that be precession?

The orientation of the plane of Iapetus' path about Saturn relative to the sun is what I'm getting at.

Posted by: BruceMoomaw Apr 15 2006, 06:41 AM

Oh, yes, it precesses. (The similar precession of Triton's even greater 23-degree tilt compared to Neptune's equator leads to fantastically complex seasonal cycles for Triton. Its most extreme seasons come along about every 700 years, and by pure coincidence the peak of its latest 175-year summer will come next year -- which seems to be having interesting effects on its surface optical properties, judging from the fuzzy Earth-based data we've gotten on it since Voyager 2. But I don't know what the seasonal cycles are for Iapetus, or for that matter for our own Moon.)

Posted by: TritonAntares Apr 15 2006, 09:15 AM

Hi!

Steve, you should probably be careful with the position of the southpole I marked in my image above:

Posted by: BruceMoomaw Apr 15 2006, 11:43 AM

QUOTE (TritonAntares @ Apr 15 2006, 09:15 AM)

Posted by: tasp Apr 15 2006, 02:27 PM

The earth's moon's orbital inclination (ref'd to earth) seems to be constant in it's orientation to the plane of the ecliptic (hence allowing the possible existence of permanently shadowed craters around the poles).

I am still fuzzy if the orientation of the Iapetan orbit around Saturn maintains a constant orientation to the ecliptic. Eath's axis manages to precess every 23,000 years or so, yet the moon doesn't stray more than (IIRC) 5 degrees or so from the ecliptic. Has the equivalents for all of this been worked out for the Saturn system? Does Saturn currently have a prominent Polaris type polestar now?

If it doesn't, does the northern and southern boundaries (diffuse though they may be) of Cassini Regio correspond roughly to the Iapetan equivalents of the earth's Tropics of Capricorn and Cancer?

If Cassini is 'pinning' down Iapetus' location to a few kilometers, perhaps subtle shifts in this would be measurable.

Posted by: David Apr 15 2006, 02:40 PM

QUOTE (tasp @ Apr 15 2006, 02:27 PM)

Posted by: angel1801 Apr 15 2006, 06:56 PM

I am here to tell you that lots of new Iapetus images are in, ranging from about 700,000 km to 820,000 km.

It is apparent from some these new images, they have finally achived some "saturnshine" images of Iapetus's south pole area.

Posted by: TritonAntares Apr 15 2006, 08:07 PM

Hi,
a large downlink of 39 images is now online.

Here some takeouts:

Posted by: Decepticon Apr 15 2006, 11:09 PM

Posted by: BruceMoomaw Apr 16 2006, 03:34 AM

QUOTE (TritonAntares @ Apr 15 2006, 09:15 AM)

Posted by: angel1801 Apr 16 2006, 06:05 AM

Looking really close to some of the over exposed shots (and making them brighter), I saw features like craters and topographic features on the south pole. ie a group of three craters close together.

I could be wrong though.

Posted by: TritonAntares Apr 16 2006, 10:54 AM

QUOTE (BruceMoomaw @ Apr 16 2006, 05:34 AM)

Posted by: TritonAntares Apr 18 2006, 01:14 AM

Hello,
next 8 Iapetus-cresents are online now.

Two Takeouts:

Posted by: ugordan Apr 18 2006, 07:37 AM

QUOTE (TritonAntares @ Apr 18 2006, 02:14 AM)

Nearly half of Iapetus should be in saturnshine.
But there is nothing visible yet.
Enhencement of the overexposure only showed me some artefacts...

Posted by: TritonAntares Apr 18 2006, 01:35 PM

So,
next 7 Iapetus-cresents from april 17th (16th was left out) are online.

Two takeouts:

Posted by: scalbers Apr 18 2006, 06:15 PM

Thought I'd mention my next Iapetus map iteration. This again has images up through 4/11/2006 and hopefully a little better consistency and south pole location. This is very much a work in progress as one might imagine so I hope to improve the coverage including perhaps additional images and to reduce navigation errors further as we go.

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

Posted by: angel1801 Apr 19 2006, 02:09 PM

Some new Iapetus images are just in.

Distances are from about 1,100,000 km to about 1,300,000 km away.

This set includes four over exposed shots.

Posted by: scalbers Apr 19 2006, 04:44 PM

Greetings,

Here's the next mapping update. Using pretty much the same images up through April 11, I adjusted the navigation a bit more and added further coverage. This includes mapping of the mysterious high terrain that is catching the light beyond the terminator. It just so happens to fill in a good bit of the gaps representing "Iapetea incognita".

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

Posted by: TritonAntares Apr 19 2006, 07:18 PM

Hi,
the obvious final Iapetus images series for this far-encounter has been transmitted,
altogether 12 pics:

Three Takeouts:

Posted by: scalbers Apr 20 2006, 04:38 PM

Looking ahead just a bit I see via Celestia that the Sep 2007 flyby should fill in the remaining gaps almost perfectly. This takes into account both Cassini and Voyager images to date.

Posted by: TritonAntares Apr 20 2006, 05:03 PM

Hi,
here a look on the improvement of our topografic knowledge of Iapetus' southern hemisphere due to this far-encounter:

Posted by: scalbers Apr 20 2006, 06:43 PM

I enjoy seeing your illustrations Triton-Antares. I'll try to do a screen capture later on to illustrate my point. I think we are saying consistent things in that the view from roughly 100000-300000km out after the closest approach could allow regional coverage of almost the entire area of gaps in the trailing hemisphere. This is reflected in your bottommost image. They could also perhaps take some WAC images closer in to get more of a large-scale view? Are there any planned images beyond the NAC real closeups plotted above?

EDIT:

This http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_sep2007.jpg might be nice to capture from Cassini. Is Celestia handling the Cassini oriented perspective reasonably?

On another note I made a new slight tweak to the map today that shows one of the craters better that you had marked in your April 17 crescent comparisons (post 141). I'm sort of glad that I pretty much have until Sep 2007 to catch up on this type of cleanup

Posted by: Rob Pinnegar Apr 20 2006, 09:23 PM

Just checking the 2007-10-09 flyby: As it happens, the closest approach to Iapetus occurs near noon UTC, so Cassini starts the day 10^5 kilometres from Iapetus, and finishes the day 10^5 kilometres from Iapetus. That's over 24 hours of approach time that will be better than what we've seen before. Lots of time for imaging.

The focus of this flyby is of course the "far side" of Iapetus, that faces away from Saturn -- but, as Cassini approaches Iapetus, the Saturn-facing "near side" of the moon will be pretty well lit by Saturnshine. So there ought to be some improvement in imaging this part of the moon, especially the trailing, Saturn-facing quarter-sphere.

Posted by: tasp Apr 21 2006, 01:01 AM

QUOTE (scalbers @ Apr 20 2006, 01:43 PM)

Posted by: ugordan Apr 21 2006, 07:14 AM

QUOTE (tasp @ Apr 21 2006, 02:01 AM)

Posted by: TritonAntares Apr 21 2006, 02:02 PM

Hi,
I'm wondering how close CASSINI will pass Iapetus on sep 10th, 2007.
I guess I've read something about 1000-1500 km, but these two simulation programs give different distances...

Solar System Simulator (2065 km):

Posted by: angel1801 Apr 21 2006, 02:15 PM

I just wonder. To keep the solar system to nine planets, which we all learnt at school and everybody has grown to love, Pluto should remain a planet NO MATTER WHAT!

Posted by: scalbers Apr 21 2006, 04:34 PM

QUOTE (TritonAntares @ Apr 21 2006, 02:02 PM)

Posted by: ljk4-1 Apr 21 2006, 04:46 PM

QUOTE (angel1801 @ Apr 21 2006, 10:15 AM)

Posted by: Michael Capobianco Apr 21 2006, 05:01 PM

QUOTE (TritonAntares @ Apr 21 2006, 10:02 AM)

Posted by: TritonAntares Apr 22 2006, 10:05 AM

Hello,
one of the many questions raised by the april far-encounter
is the exact position of this mountain at the border of eastern CR.
To remember, these illustrations:

Date: 2006/04/01

Posted by: scalbers Apr 22 2006, 02:35 PM

Hello Triton-Antares,

An initial quick comment would be that what I see as a crater circled in your middle image is the same one at the very bottom (left) of the map section you show in the lower image. This is actually the same crater I cleaned up a bit in my latest map version from April 20. This is also circled by you in post 141.

This may be different from the mountain you show in the top image. Could this be the Snowman crater central peak? Perhaps some reprojecting experiments can help address this as you suggest.

Addendum:

Oops, correct "bottom (left)" to read "bottom (right)". I'll try to edit this later when I'm working on a real computer.

Posted by: Michael Capobianco Apr 22 2006, 04:20 PM

Here are Saturn Viewer results for

April 1:

Posted by: tasp Apr 22 2006, 08:01 PM

TritonAntares, thanx for posting the equatorial white peaks picture.

If I am orienting this all in my head correctly, the peaks are experiencing (more or less), high noon as Iapetus passes directly sunward of Saturn.

Additionally, the north south extent of the 'stain' is dramatically 'necking down' in their range of longitude.

My thinking again turns to insolation as a causitive factor for CR. Steep sides of isolated peaks along the equator would be tough surfaces to build up significant (relative to the rest of Iapetus) heating from sunlight impingement. A gaseous material temporarily in the vicinity of Iapetus requiring heat to polymerize and fall to and stain the surface again being plausible. The gaseous materials either dissipate to the void in less than 80 days, or react to the warm surface and are consumed.

The gas would be replenished during Iapetan traverses of the Saturn magnetotail when it is transporting larger amounts of gas from the Titan atmosphere freed by big impacts, or perhaps a slow steady drizzle (spritz?) of simply leaked atmosphere.

The gas is always 'applied' to Iapetus in the same place in its' orbit about Saturn, and Iapetus always turns the same face sunward after every application for the insolation to 'paint' the 'sludgified' gas onto the surface.

South facing crater walls in the northern hemisphere of Iapetus, and the north facing crater walls in the south, are able to maintain their needed angle to the incoming sunlight to maintain their temps for this reaction to occur furhter north and south than average.

Posted by: TritonAntares Apr 23 2006, 11:08 PM

QUOTE (tasp @ Apr 22 2006, 10:01 PM)

Posted by: tasp Apr 24 2006, 01:12 AM

My best response to your excellent point will be that we need to wait for comparable higher resolution photos of the mid southern to far southern latitudes if we don't already have them.

Had not considered this aspect of the puzzle.

I will assert symmetrical poleward craterwall darkening on both the northern and southern hemispheres of Iapetus are required for the thermosensitive gaseous discolorant idea.

Make or break prediction if you will.

I'll go check swampcats processed images over at SDC . . . .

Posted by: tasp Apr 24 2006, 01:38 AM

I haven't really found (after a brief search) comparable pictures of the poleward crater wall darkening effect for the southern hemisphere. The distant whole disc shots taken from the ~equatorial plane show similar polar area motling or stipling, but I do not find that conclusive.

As Spock says, fascinating . . . .

Posted by: volcanopele Apr 24 2006, 07:37 PM

QUOTE (TritonAntares @ Apr 21 2006, 07:02 AM)

Btw,
IAU should finally have given names to new found iapetean structures till then.
Roughly 1,5 years. It's time enough....
Or are they overwhelmed with deciding whether Pluto or UB313 are planets or not...?

Posted by: TritonAntares Apr 25 2006, 08:47 AM

QUOTE (volcanopele @ Apr 24 2006, 09:37 PM)

Posted by: angel1801 Apr 25 2006, 09:33 AM

I am glad that the IAU is finally getting around to name all those new features on Enceladus, Dione, Rhea, Iapetus, Tethys and Mimas. Is there a website available so we can see the current status on this process?

Posted by: TritonAntares Apr 26 2006, 12:02 AM

Hello,
I tried again to locate the mountain visible on the images of april 15th more accurately:

Posted by: scalbers Apr 26 2006, 06:52 PM

Triton-Antares,

If I can partly address this, I believe the red circle in the upper right crescent image coincides with the (this time unmarked) crater at the very bottom (left) of the section shown from my map.

Posted by: TritonAntares Apr 26 2006, 08:44 PM

Hi Steve,
I think you mean the green encircled crater on your map (probable mountain in rectangle):

Posted by: scalbers Apr 26 2006, 11:02 PM

Triton-Antares,

I am gathering some additional evidence that supports the conclusion that the green feature in the map at bottom (of your post) is the same as the red in the raw image at top. I took the April 15 image and ran it through my software. Comparing the cylindrically projected image shows this fairly clearly. The http://laps.noaa.gov/albers/sos/saturn/iapetus/ortho30_gridded.jpg on the raw image is here. The navigation was just done roughly but should be close enough to establish my hypothesis. A test map with just this image projected on it helps to clinch the case at the URL below:

http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl_30.jpg

Posted by: TritonAntares Apr 29 2006, 09:24 PM

Hello,
I tried again to identify some topografic structures of the latest Iapetus far-encounter.
This time I compared the the april 15th cresent-image with two from january 2006 and the map:

Posted by: scalbers May 3 2006, 09:36 PM

Yes, the terminator really brings out the shadows and topographic relief. Overall that's quite a nice and colorful comparison of features from different vantage points. In looking at the 1/22/2006 image I realized it could add coverage to my map (every square degree counts ) so I have now updated this:

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

Might also be interesting to continue the comparison using a south-pole centered version of the map. I may try to reproject it sometime. Using Celestia can work though that software introduces quite a few artifacts near the pole.

Posted by: Phil Stooke May 4 2006, 07:04 PM

I'll do a south polar view when I'm back in my office.

Phil

Posted by: TritonAntares May 5 2006, 11:40 AM

Hi,
let me mention, there will be another Iapetus campaign between june 17th and 27th.
Unfortunately minimum distance will only be around 1,3 mio. km, resolution about 8,1 pxl/km.

Here a short animation done with Celestia:
 Iapetus_june_2006.avi.html ( 373K ) : 941

Just remove *.html and run the avi-file preferably on a DIVX-player.

Bye.

Posted by: angel1801 May 5 2006, 02:31 PM

QUOTE (TritonAntares @ May 5 2006, 09:10 PM)

Hi,
let me mention, there will be another Iapetus campaign between june 17th and 27th.
Unfortunately minimum distance will only be around 1,3 mio. km, resolution about 8,1 pxl/km.

Here a short animation done with Celestia:
 Iapetus_june_2006.avi.html ( 373K ) : 941

Just remove *.html and run the avi-file preferably on a DIVX-player.

Bye.

Posted by: TritonAntares May 7 2006, 11:01 AM

QUOTE (angel1801 @ May 5 2006, 03:31 PM)

Posted by: angel1801 May 7 2006, 07:50 PM

QUOTE (TritonAntares @ May 7 2006, 08:31 PM)

Posted by: JRehling May 7 2006, 08:13 PM

QUOTE (angel1801 @ May 7 2006, 12:50 PM)

Posted by: scalbers May 12 2006, 11:26 PM

Greetings,

I went ahead and set up a south polar view of Iapetus in a perspective projection. This is based on my recent map updates and can be seen at the URL shown below. It might be interesting to compare this with some of the individual images.

http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus_rgb_cyl_www_P1.jpg

Posted by: Decepticon May 20 2006, 04:01 AM

Posted by: scalbers May 20 2006, 03:52 PM

Well Decepticon it could be useful, depending on where the imaging is done. I'll have to look at the animation again in the office, though I recall it seemed to mostly cover familiar territory. You might consider that on my map there are a variety of resolutions used depending on location. I know I had used images from 1.3millon km and farther though much of that territory has since been superseded by closer images. Clearly if you're in some of the blank areas any resolution would be helpful. So we might have check in more detail to more fully answer your question.

One fun thing I've been developing in my software is an option allowing me to overlay an image automatically only in those areas where the resolution (coupled with spacecraft zenith angle) represents an improvement. While other factors (such as phase angle, etc.) should also be considered it's interesting to see where a new image gets pulled in.

Posted by: TritonAntares May 22 2006, 03:13 PM

Hi some 'colorful' news from Iapetus,
http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2140 a nice pic-pair from the JPL-site:
http://photojournal.jpl.nasa.gov/jpeg/PIA08164.jpg
Monochrome image:
Date: 2006-04-08
Distance: 866.000 km
Resolution: 5 km/pxl

Color image:
Date: 2006-04-09
Distance: 692.000 km
Resolution: 4 km/pxl

Bye.

Posted by: BruceMoomaw May 23 2006, 01:28 AM

Lovely piece of work. (And don't forget that good color images of Iapetus are scientifically important, since the dark material extending onto the trailing side of Iapetus seems to be distinctly less reddish than that on the leading side, supporting the new theory that the shape of the dark and light regions has been modified by the effects of warming by sunlight.)

Posted by: scalbers May 23 2006, 05:06 PM

Very interesting to learn more about the pattern of colors on Iapetus. I wonder if this image is corrected to look like an RGB image would (i.e. "near-true" color) or should be categorized as false color since it is taken with the UV, G, and IR filters? Curious that CR maybe looks a bit yellower than in some of the other color releases.

Posted by: ugordan May 23 2006, 06:27 PM

I'd venture to say the image looks so funny, compared to previous "true" color and false color images is because they used the IR3 filter in place of the IR1 usually used for stretched, "true-like" color (IR1-GRN-UV3). I had similar results pop up using the PDS data from the New Years flyby.