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Posted by: TritonAntares Jun 1 2006, 04:30 PM

Hi,
as june begins, time to open this thread...

As said before there will be another Iapetus campaign in the second half of this month - from 17th until 27th.
Unfortunately the minimum distance will only be around 1,3 mio. km, resolution about 8,1 pxl/km.

Also the short Celestia-animation again:
 Iapetus_june_2006.avi.html ( 373K ) : 816

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

Bye.

Posted by: jsheff Jun 1 2006, 08:49 PM

That's very cool! Thank you. I've used Celestia before but not to the extent of simulating a flyby. Now that I know it can be done, I'm going to use it.

- John Sheff

Posted by: scalbers Jun 3 2006, 02:45 PM

Greetings,

Thought I'd mention that I'm continuing to work on some map refinements, particularly to improve the consistency of features near the S/SE boundary of Cassini Regio. The lumpy shape of Iapetus, especially at high southern latitudes, makes it a bit challenging to reproject images onto consistent map locations given the assumption of a spherical (or even ellipsoidal) shape. I wonder if it's worth the exercise of improving my software to optionally include a shape model. Does anyone happen to have an extra shape model for Iapetus lying around? Perhaps I can learn to generate one myself using limb and/or feature fitting?

Posted by: TritonAntares Jun 7 2006, 07:38 PM

Hi,
the first two june-shots of Iapetus are online.

Here an enlargement:

Date: 2006-06-05
Distance: 4.212.487 km (!)
Filters: CL1 and CL2

Remarkable the 2 giant impact bassins, one at the dark-bright border and the other one at the bottom - more difficult to see - in the dark area.

Bye.

Posted by: volcanopele Jun 8 2006, 06:04 PM

What are you assuming for the ellisoidal shape? Are using a=747.1, b=749, c=712.6?

Posted by: scalbers Jun 8 2006, 06:50 PM

VP,

It turns out I'm still using a spherical shape for Iapetus. I recently noted both a triaxial one (probably the one you mention) as well as an oblate spheroid one using a Google search of some literature. The two were so different I wasn't sure how much benefit using either would be. Perhaps the one you mention is more recent? The main point is that even a triaxial ellipsoid may be only a rough approximation in the vicinity of both the south polar region and the belly band. Perhaps its worth a try though.

I have so far used triaxial ellipsoids just in my Mimas and Enceladus map processing.

At any rate I've managed to get some improved consistency of the features in southern CR in my latest map update at http://laps.noaa.gov/albers/sos/sos.html#IAPETUS. This version includes PIA08164 from the April flyby.

Posted by: volcanopele Jun 8 2006, 07:25 PM

The one I quoted is the most recent one from cassini observations and is in Thomas et al. 2006 (from LPSC, abtract 1639). See if that helps you any.

Posted by: TritonAntares Jun 12 2006, 08:36 PM

Hello,
the next Iapetus-pic is online.

Here an ~4x enlargement:

Date: 2006-06-08
Distance: 3.822.476 km (!)
Filters: CL1 and CL2

No greater change...

Bye.

Posted by: TritonAntares Jun 15 2006, 07:47 PM

Hi,
additional Iapetus-images are online.

Here a takeout , ~4x enlargement:

Date: 2006-06-14
Distance: 2.841.146 km
Filters: CL1 and GRN

To recognize the different bassins, a view through the Solar System Simulator:


Bye.

Posted by: TritonAntares Jun 18 2006, 07:58 PM

Hi,
a full battery of 37 Iapetus pics has been released .

Here two takeouts , ~3x enlargement:

Date: 2006-06-17
Distance: 2.220.917 km
Filters: IR2 and CL2


Date: 2006-06-17
Distance: 2.219.152 km
Filters: P60 and MT2

An overview through the Solar System Simulator:


Bye.

Posted by: TritonAntares Jun 21 2006, 10:03 AM

So,
another 51 Iapetus pics are online.

Here two takeouts , ~3x enlargement:

Date: 2006-06-20
Distance: 1.652.638 km
Filters: P0 and GRN


Date: 2006-06-20
Distance: 1.651.831 km
Filters: CL1 and CL2
Quite tall mountain visible on the right limb!

Overview through the Solar System Simulator:


Bye.

Posted by: TritonAntares Jun 23 2006, 09:28 AM

Hi,
CASSINI transmitted further 31 Iapetus images.
Some widefield pics are also among them - maybe some positioning control or do they probably try to find some Iapetus coorbitals?
But these should be about 30° before or behind Iapetus...
This was taken:
June 21st - 11 tele/4 widefield pics
June 22nd - 14 tele/2 widefield pics

Here two takeouts , ~3x enlargement:

Date: 2006-06-22
Distance: 1.398.591 km
Filters: CL1 and CL2


Date: 2006-06-22
Distance: 1.398.128 km
Filters: P60 and MT2

And a widefield view:

Date: 2006-06-22
Distance: 1.396.785 km
Filters: CL1 and CL2

Overview through the Solar System Simulator:


Bye.

Posted by: Decepticon Jun 23 2006, 12:12 PM

Looking good!

Posted by: ugordan Jun 23 2006, 02:34 PM

Make that 60°... definitely much more than the wide angle field of view. This was a long exposure image, perhaps for optical navigation purposes.

Posted by: TritonAntares Jun 23 2006, 06:20 PM

Yes, of course 60° - the Lagrangian points...

Posted by: TritonAntares Jun 24 2006, 11:05 AM

Hi,
back again with some weird pics from Iapetus...
An astonishing number of 151 images was taken on june 23rd alone.
But there are 124 among them showing only star fields - no Iapetus at all!
And these are no widefields!
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-list.cfm?StartRow=1&cacheQ=1&browseLatest=0&storedQ=1282780
Are they probably trying to find some Iapetus moons? Or are thes pics taken at the Lagrangian points?

This was taken:
124 starfields
7 widefields
14 tele pics
6 half-Iapetian overexposures (3 of each half)

Here some takeouts, ~3x enlargement:

Date: 2006-06-23
Distance: 1.343.121 km
Filters: CL1 and IR3


Date: 2006-06-23
Distance: 1.343.092 km
Filters: P120 and UV3
Note, the 'Moat / Snowman' is slowly getting visible at the right limb!

Here two overexposured halfs stacked together:

Date: 2006-06-23
Distance: ~1.343.200 km
Filters: CL1 and CL2

Overview through the Solar System Simulator:


Bye.

Posted by: Rob Pinnegar Jun 24 2006, 02:26 PM

You might be right about the idea of looking for Iapetan Trojans. Notice that there is a fair amount of "smear" in these images. They might be deliberately rotating the camera during the exposure, to keep the Lagrange point steady in the image while the spacecraft moves. (If I remember right, this was the technique that was used to find the first few small KBOs in the 1990s.)

Looking for Iapetan Trojans is a worthwhile endeavour -- if any are found, that'd have some pretty important implications for the evolution of Iapetus' orbit over time. Since Cassini doesn't have much else to photograph all the way out there (other than Iapetus) this'd be a good time to do it.

Posted by: ugordan Jun 24 2006, 05:21 PM

I don't see why being near Iapetus would make a better opportunity than any other point in the orbit. The potential trojans aren't that close to the moon anyway. The area of the sky needed to be surveyed is probably pretty large which would require WAC coverage (thus you can't catcg very small objects) or many NAC footprints.
The huge number of empty starfield images seems to me to be another case of bad pointing. It seems as if something threw Cassini's attitude off balance, see http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=77691 for example. It was obviously 'tracking' something, but pretty erratically. In some other NAC frames Iapetus is just http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=77688. It might be the case of ISS riding along some other instrument that slews across Iapetus and empty space, like CIRS or the sort.
Maybe volcanopele can shed some more light on this.

Posted by: scalbers Jun 24 2006, 05:27 PM

Triton-Antares' top image in post #16 is nice to see as the features near the S edge of CR below the center are all grouped together in one image. In many of the previous images one sees just a subset of these features near the limb or terminator. This may be helpful in checking image navigation, etc.

Posted by: TritonAntares Jun 25 2006, 11:01 AM

Hi,
the next Iapetus image series is online, this time 47 pics.

This was taken:
24 starfields
6 widefields
17 tele pics including 3 overexposures

Here some takeouts, ~3x enlargement:

Date: 2006-06-24
Distance: 1.368.986 km
Filters: CL1 and IR3


Date: 2006-06-24
Distance: 1.416.632 km
Filters: CL1 and CL2
Hence CASSINI is slowly diverging from Iapetus,
really too bad that the 'Moat / Snowman' is now getting more and more visible at the right limb...

Overview through the Solar System Simulator:


Btw.,
any news on those starfield images?

Bye.

Posted by: TritonAntares Jun 25 2006, 01:45 PM

Hi,
I'm still curious about those starfield images, but I don't believe that they're tracking errors.
In many pics Iapetus is pointed exactly!
The only sense for taking those starfields I could guess is the finding of moons in the vicinity of Iapetus or Iapetian trojans 60° apart.

120° field of view from Saturn showing Iapetus and CASSINI,
the Lagrangian points therefore are at the left and right image border:

Of course CASSINI is not at one of those Lagrangian points but as close to them as it can get in its orbit
and there is plenty of time to take these photographs now even if there is no other target than Iapetus.

Bye.

Posted by: tasp Jun 25 2006, 02:01 PM

Cassini might be looking for plumes . . . . .



(btw, there won't be any plumes at Iapetus, but it is good science to take the images and confirm)

Posted by: ugordan Jun 25 2006, 02:50 PM

I don't buy it. Plumes would be very hard to spot from this phase angle. You'd still have to watch Iapetus' limb, not point in a random direction.
This new image batch is precisely pointed as you suggest, but that doesn't preclude the possibility they did one of those Inertial Vector Propagator updates in the meantime. Though, I'm more inclined to say it looks like a sequencing error than bad ephemeris at this time.

Posted by: nprev Jun 25 2006, 06:27 PM

Just out of curiosity, does anyone know if the ESA Cassini trajectory/simulation page is still reasonably accurate? Here's the link:http://www.esa.int/SPECIALS/Cassini-Huygens/SEMD6E2VQUD_0.html

Posted by: TritonAntares Jun 26 2006, 09:19 AM

Hi,
this time only one pic has been transmitted.

Here the takeout, ~3x enlargement:

Date: 2006-06-25
Distance: 1.569.770 km
Filters: CL1 and CL2

View through the Solar System Simulator:


Bye.

Posted by: TritonAntares Jun 28 2006, 09:41 AM

Hi,
Four additional pics have been transmitted,
2 WACs and NACs.

Here a Takeout, ~3x enlargement:

Date: 2006-06-27
Distance: 1.942.690 km
Filters: CL1 and UV3
Sad, as the 'Snowman' is getting more and more visible the image details are vanishing...
Note the bulge - probably a mountain range or the outer rim of a bassin - at the right limb at roughly 4 o'clock!

View through the Solar System Simulator:


Btw.,
Tilmann Denk informed me on a german forum that those widefields taken during the last days were actually done to find small moons in the vicinity of Iapetus.
One widefield is able to catch the the so called Hill-sphere around Iapetus.
The NACs were taken additionally in the same area, but due to time and memory reasons it was not manageable to cover the whole area around Iapetus with those 'footprints'.
Let me add that no pics at the Lagrangian points were taken.

Bye.

Posted by: Decepticon Jun 28 2006, 01:29 PM

I tried to stack the image. Another image would have helped.

Posted by: Rob Pinnegar Jul 1 2006, 05:14 PM

This seems to be just about "it" for Iapetus encounters until the targeted flyby in September of next year. Cassini will get within a couple of million kilometres of Iapetus a few more times before then, but we won't really be seeing anything new, or closer views of things already seen, on those occasions.

Posted by: TritonAntares Jul 3 2006, 04:20 PM

Here a collection of Iapetus far-encounters I found until September 2007 using Solar System Viewer:
2006-09-03 / 1.816.000 km:


~11 km/pxl; sub-Saturn
Iapetus as we are used to observe it.

2006-09-15 / 2.288.000 km:

~13 km/pxl; Moat/Snowman in center
Interesting sight, hopefully some OPNAVs!

2006-11-27 / 1.997.000 km:

~12 km/pxl; very low phase, sub-Saturn
And again the same Iapetus regions...

2006-12-11 / 2.699.000 km:

~16 km/pxl; half phase, rim of eastern CR at terminator
All known territory, distance too far...

2007-01-18 / 2.565.000 km:


~15 km/pxl; cresent, Moat/Snowman at terminator
Quite interesting view, but probably too far away.

2007-02-14 / 2.249.000 km:

~13,5 km/pxl; sub-Saturn
Once again Iapetus as we are used to observe it.

2007-03-25 / 2.614.000 km:

~15,5 km/pxl; sub-Saturn
Iapetus in the dark, maybe some limb topogaphics visible.

2007-04-15 / 2.256.000 km:

~13,5 km/pxl; Moat/Snowman and northern hemisphere
Interesting perspective of some badly known regions, but quite far away...

2007-06-22 / 1.817.000 km:

~11 km/pxl; sub-Saturn
Iapetus in the dark again, maybe some limb topogaphics visible.

2007-07-05 / 2.281.000 km:

~14 km/pxl; Moat/Snowman and unknown southern giant bassin
For sure the most interesting perspective, sadly only 2 months before the fly-by.

Even though all these encounters are between 1,8 and 2,7 mio km, there are some perspectives we haven't seen so far.
I'm curious about which opportunities will be taken to look again at this saturnian moon?!

Bye.

Posted by: Michael Capobianco Jul 3 2006, 06:47 PM

Thanks, TritonAntares, for putting together that Iapetus itinerary and all the image summaries. I have the feeling that any images that are taken during those passes will be more frustrating than informative. But with this moon, frustration is half the fun!

Michael

Posted by: TritonAntares Jul 24 2006, 06:47 PM

Hi,
I've just checked the CASSINI image gallery and found these two pics transmitted at the begin of july:

Here the takeouts, ~4x enlargement:

Date: 2006-07-06
Distance: 4.375.899 km
Filters: CL1 and CL2

View through the Solar System Simulator:

---------------------------------------------------------

Date: 2006-07-08
Distance: 4.585.762 km
Filters: CL1 and CL2

View through the Solar System Simulator:


Unfortunately there has no unknown terrain been mapped...

Bye.

Posted by: TritonAntares Aug 3 2006, 12:30 AM

Hi,
I've just noticed this image release:

Date: 2006-06-25
Distance: ~ 1.6 mio. km
Resolution: 9 km per pixel

Very nice work...

Bye.

Posted by: TritonAntares Aug 22 2006, 10:25 AM

Hi after a longer time!

CASSINI is occasionally taking Iapetus images,
three have been transmitted during august so far:

Here the takeouts, ~4x enlargement:

Date: 2006-08-14
Distance: 4.671.693 km
Filters: CL1 and CL2

View through the Solar System Simulator:

---------------------------------------------------------

Date: 2006-08-19
Distance: 2.694.772 km
Filters: CL1 and CL2
Note the dark rings of the 'moat'/'snowman'...

View through the Solar System Simulator:


Btw., closed approach for this orbit will be on sep-02:


No new lands...

Bye.

Posted by: CAP-Team Aug 23 2006, 10:13 AM

I usually use xplanet with Steve Albers' maps.
This image simulates the Cassini view of Iapetus on 19 August 2006 12:40 UTC.