Hi,
let me open this thread on the closest Iapetus flyby on September 10th later this year.
Hopefully we'll get some more clues to solve the mysteries of this odd moon, like the origin of the equatorial ridge and the brightness differance...

First, some new infos given by Tilmann Denk from FU Berlin:
CASSINI will pass Iapetus in roughly 1600 km.
An UVIS star occultation of sigma Sagitarii will now occur about 1 hour before closest approach - instead of during it.
This will now allow an additional window for high resolved pics of the highest known parts of the equatorial ridge at 160°
(phase between ~140° and ~30°) now, apparently a decisive approvement of this encounter.
Detailed planing can be started soon...



Bye.

I may have posted this view somewhere using my map along with Celestia, illustrating the unseen terrain to be imaged...

http://laps.noaa.gov/albers/sos/saturn/iap...tus_sep2007.jpg

This new abstract on the "White Mountains" has popped up on the Voyager-Pioneer thread recently:

http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1596.pdf

The notion that these mountains could have been created by a large meteorite that hit Iapetus at low speed and broke into pieces seems awfully weak. Is that supposed to explain why most of them are lined up with the "belly band", and why they're white while most of the terrain around them is black?

Iapetus seems to be good at getting people to grab at straws when it comes to theorizing. Sometimes it's better simply to admit that you don't know. Given that we've never seen those mountains in decent detail, there's no shame in that.

Yes, there's a lot of speculation about Iapetus and its strange anomalies...
But with a lack of well resolved imagery - what should be expected else?

Referring to the 'white mountains', here a point I posted about a year ago:
Visible is a large bassin in the western part of CR (inside the large green circle)
cut by the part of the ridge with the 'white peaks' (red line).
Click to view attachment
My impression is that its central peak (small green circle) doesn't coincide with the 'white peak' NW of it and it is also lower.
Thus the crater must be older than the 'white mountains'.
This 'white peak' seems to cast an enormous shadow (blue quadrangle) to its western side.
Is the equatorial ridge interrupted there?
Is there any ridge at all or only these 'white peaks'?

We'll see on September 10th ...

Till then, a 3-dimensional topographic analysis of the shadow casting in this region would be quite interesting I guess.
Anyone out there taking the task?

Bye.

Hi,
a global mosaic of the trailing side consisting of 15 footprints is now fixed. Resolution will be 422-456 m/pxl.
Final planning on other mosaics (particularly the 'White Mountains') will be completed in May.

Bye.

Hi again,
some more infos on the september fly-by:
The observation window for the VIMS/ISS-request during closest approach will be about 4 hours (13:27 - 17:16 UTC),
image resolution of the ISS-telecamera 40...10...148 m/pxl.

A 2+2+3-mosaic of the equatorial ridge at 140° will first be taken under high phase angle.
Then the 'White moutains' (higher then 20 km?) will be imaged by WAC (~150 m/pxl).
During closest approach as phase angle will rapidly decline the equator region at 165° will be observed.
(at this longitude the ridge is presumably coming to an abrupt end).

After closest approach a scan with CIRS-spectrometer will be conducted at 12°S/168°W ('average dark terrain'), followed by a CIRS-Scan at 42°S/209°W ('average bright terrain').
Next a 1x6-mosaic of the 'White moutains' - now at low phase angle - will be taken. 1 hour after closest approach NAC resolution will be 40-50 m/pxl for this mosaic.
After that some infrarotspectrometer (VIMS) observations will be conducted, longitude hasn't been chosen so far.
A large mosaic of the equatorial transition zone from west (~190°W) to east (~250°W) as 3x4 + 3x3 mosaic will be taken next. Duration roughly 1 hour, resolution 80-130 m/pxl.
Next there will be a 'terminator mapping' at 300°W, followed by the attempt to capure the 'Moat' in saturnshine.
Other observations will follow, e.g. the mentioned global mosaic of the trailing side consisting of 15 footprints (422-456 m/pxl).

Final planning for the fly-by will be finished by end of May, as Tilmann Denk from FU Berlin informed me.

Bye.

...some additional infos I recieved from Tilmann Denk yesterday:

During approach (Iapetus in high phase) polar regions of the saturn facing side should be imaged in saturnshine - resolution ~480 m/pxl.
Also NAC of the peaks will be taken (~15 m/pxl), but exact pointing roughly 15 minutes before closest approach to Iapetus needs a bit luck as their position isn't precisely known. Furthermore the 'white peaks' will overfill the field of view...
Luckily 1-2 NACs could show the sun averted side of one of those peaks.

Saturnshine imaging of the 'Snowman' will be conducted from 24000 km, 77000 km and 101000 km, maximal resolution ~150 m/pxl, for sure an improvement to saturnshine pics from 2005-01-01.
As blurring from radial movement is roughly about 2 pixels the closest series will be exposed for only 18 sec - hopefully long enough...

The nearly unknown large basin in southern Roncevaux Terra will eventually get some attention around closest approach - resolution then ~250 m/pxl. But planning isn' t fixed so far...

A global sight (1.6 km/pxl) showing the whole trailing side - and certainly the basin - will be shot from 260000 km after the fly-by.
Click to view attachment

All information is primarily and there could/will be some changes and additions until the end of may.
Perhaps then we will also enjoy a new 'footprint map'...

Bye.

I'm really looking forward to this flyby. We should get some spectacular imagery, hopefully topping even Phoebe and Hyperion closeups. After several years of blurry looks through Titan's haze and bland/grayish moons, a little albedo difference and color should remind us just what ISS is capable.

I just hope those pesky gremlins won't decide to jump in on this unique opportunity and spoil the fun.

I'm still surprised about the fact that the 'white mountains' won't fit the field of view of the NACs 15 minutes apart from closest approach...

But I remember this Dione view from 2005-10-11:
Click to view attachment
It's part of this mosaic taken from ~20000 km distance:

Simply breathtaking...

And now imagine, CASSINI will pass Iapetus in 1600 km minimum distance -
what a sight of this white peaks, the equatorial ridge and a structure not mentioned so far,
the 'dark triangle' seen in this simulation:
Click to view attachment
What the heck is this?

Bye.

Seeing how it appears in Solar System Simulator's map of Iapetus that I always found weird because it practically totally washed out (artificially) contrast and color between dark and bright terrain, it looks clear that it's just a dark patch that was left unprocessed. This idea is further reinforced when one compares that map to Steve Albers' Iapetus map (link) which retains more contrast. The "triangle" there is consistent with the brightness of rest of Cassini Regio.

Yes, of course the 'dark triangle' (green) has the same brownish color as Cassini Regio.
It seems to be made up of the dark floors of 2 midsized craters.

Other dark floored impacts (orange circles) join them in the bright area around.
High interesting region to get more information about the origin of the dark material and probably solve this mystery.
I marked the 'White peaks/Voyager Mountains' with blue crosses - some of them may be questionable.
Click to view attachment
And a series of some old Voyager pics showing the peaks at the limb:
Click to view attachment(Source: Lunar and planetary science XXXI - Iapetus: Size, Topography, Surface Structures, Craters )
I tried to mark them in the part of Steve's map (A-G).

Also visible on the map is this old large crater in the west of Cassini Regio I mentioned in post #4 above.
It seems to be older than the white peaks inside and thus older than the equatorial ridge of which the peaks are presumably part of.

Bye.

While having a closer look at Steve's map I got aware of a structure not mentioned before as far as I remember:
Click to view attachment

If it's real it must be the largest basin on Iapetus.
The northern part of Roncevaux Terra was imaged in saturnshine, so contrast is rather low
and you don't really get aware of its rim compared to that of the basin in eastern Cassini Regio.

Bye.

Btw.,
some nomenclature of craters in northern Roncevaux Terra:
Click to view attachment

All craters are named after characters from the 'The Song of Roland' -
the oldest major work of French literature, composed between 1075 and 1110.
This link also offers a list of all acting characters - so we've got some names left for all those craters in Roncevaux Terra still unnamed...

After Sep.10th IAU will hopefully eventually carry on giving offical iapetean designations.

Bye.

TritonAntares that's an interesting image you are showing in post #12 with the possible basin outlines. I have part of that region on my map, and I wonder if the image you are showing can be filtered enough to remove the glare (if it can add territory to the map).

By the way I've made a new Iapetus map update. Time flies as it's the first update in about 11 months. I was able to refer to Ugordon's image to get my bearings better and the new map has more consistent navigation of the images in the southern portions of the Saturn facing hemisphere (near the edges at zero degrees longitude). I may try making some south polar views to help check/refine things further.

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

Hi Steve,

I must admit it was not your map I used for this section of northern Roncevaux Terra...
Click to view attachment

Compare these 2 maps:


-click to enlarge-


Bye.

Hi,

here a nice animation Tilmann Denk posted lately:
Click to view attachment

It shows the area (yellow line) visible from Cassini 20 min before until 20 min after closest approach. C/A at 2007-09-10, 14:15:40 UTC (16:15:40 MESZ).
As the field of view of both cameras (NAC & WAC) is much smaller than the theoretical observable area we'll only get images of some parts inside - exact footprints can hopefully be added soon.
The blue line marks the terminator - images in saturnshine are planned as mentioned above, but in a later stage of the encounter.

SSP -> sub-solar point
S/C -> sub-spacecraft point

Bye.

{Sorry if this has already been asked and answered}

Have we pinned down whether or not Cassini can take a picture faster than once a minute ??

The short answer would be: yes.
The long answer would be: depends.

There are a number of factors determining the timeout for the next picture, for an explanation of the specifics refer to Porco et. al., section 3.7 (page 457). Depending on whether NAC and WAC are used simultaneously, image compression type, telemetry pickup rates and other instrument (VIMS, CIRS... ) simultaneous operation, a typical 1x1 binned ISS frame will take somewhere from 30 to 60 seconds before the next one can be taken. 45-ish seconds is a good rule of thumb IIRC.

I think it's reasonable to expect no more than 50 frames from WAC and NAC (so 100-ish total) in the 40 minute timeframe of the above animation.

Hi,

I think I should put this here:
Click to view attachment
Really deep hit there - but also the height of the equatorial mountain range above the 'Snow Man' is striking!

Bye.

Thought you might enjoy that one. If anyone is an advocate for snowmen, it's you.

Whoa. What's the source for that image?

EDIT: Ah, nevermind, found it.

Hi,

lately arrived - these two 'footprint maps' of the fly-by:

(1) Inbound before C/A:
Click to view attachment
...

...
(2) Outbound after C/A:
Click to view attachment

I'll add some infos about resolution (different footprint colors) and camera types (NAC/WAC) later...

Bye.

Comparing the DEM and the global maps, we see another segment of the equatorial mountain ridge. It really is global, as TritonAntares said above. Truly bizarre. I'm not happy with any of the suggestions for its formation, but I draw a complete blank when I try to figure it out.

Phil

Could someone put up a link to the source of that topographic map? I've looked in several of the usual places for it, and can't find it for some reason. Is there more where that came from?

Edit: Never mind, here's the link; and there *isn't* more where that came from:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2305.pdf

(1) Inbound:
|-> equatorial ridge under high phase (~120° ) / ~30 m/pxl (NAC)
|-> Voyager mountains under 90° phase at the horizon in WAC
|-> observations around C/A: phase 83° to 29° in 18,25 minutes / 10 m/pxl (NAC)
yellow lines-> change of limb from CASSINI
blue lines-> terminator

(2) Outbound:
|-> observations around C/A: phase 83° to 29° in 18,25 minutes / 10 m/pxl (NAC)
|-> dark-bright transition zone at medium latitudes, ~250 m/pxl (WAC)/ ~50 m/pxl (NAC)
|-> Voyager mountains, NAC ~45 m/pxl (NAC) + 1 WAC
|-> 2 small boxes more left, 25 minutes for VIMS-spectrometer
|-> mosaic of equatorial transition zone, ~1h / ~100 m/pxl (NAC) + 1 WAC
|-> terminator left / ~140 m/pxl (NAC) + Snowman in saturnshine (low phase)
|-> 15 pics mosaic, ~440 m/pxl (NAC)
Borders for last series:
yellow lines-> limb from CASSINI
blue lines-> terminator

We'll see a variety of surface structures, only one image (orange box) is sadly missing in the light green and blue mosaics:
Click to view attachment
The great southern Roncevaux Terra Basin will show up under lower resolution in pic 3, 4, 5 and 6.

Finally let me thank Tilmann Denk for sharing these 2 illustrations!

Bye.

And thanks, Trtion Antares, for sharing them in UMSF. I have looked forward to this encounter from before SOI, and the excitement continues to build.

There's a new Iapetus color image on Cassini's home page: http://saturn.jpl.nasa.gov/multimedia/imag...fm?imageID=2621
It hasn't appeared on CICLOPS yet, probably within an hour of two.

As far as I know, this is the first actually "natural" color image of Iapetus released by the imaging team where they used RGB filters instead of infrared/ultraviolet filters. While the image itself is magnified and Cassini Regio is barely visible, it shows what I've been pointing out for a while, the color of the dark stuff is much subtler than the "cool" chocolate appearance portrayed in all previous CICLOPS composites.

This latest color image is more consistent with approx. natural color composites such as this one and this sequence. See this animation for a typical example of previous false color views for comparison.

Wow, almost a black and white image!

That particular image looks b/w because the bright ice is so much brighter than Cassini Regio the latter turns out very dark and color is practically lost. It does have color (even a bit of detectable color variation in approx. natural colored images), but it's best seen on views centered on the leading side (basically all earlier Cassini views) so image brightness can be optimized for low albedo material without overexposing the brighter (some 10x brighter) ice. If the color were as pronounced as in those enhanced color views, there still would be color visible even in this low resolution view.

Had that image been scaled up to brightnesses of this composite, the "clean" ice visible would be severely overexposed. Iapetus is all about contrast.

Fortunately now there will be a 250 m/pxl look at this basin - not highest resolved, but a 3 color summation mode and a full-resolution clear image...
Click to view attachment

This footprint was luckily added ahead of the VIMS_049IA_IAPETUS013_PRIME images (rectangles above).

Bye.

...btw,
as Celestia isn't installed on my Computer right now - and I'm to sluggish to do it this evening - may be SOMEBODY on this forum could be so kind to create and post an animation of September's fly-by using this map:
Click to view attachment
(180° correction was done)

THX & Good night!

Hi - after a while...

A pity no one using Celestia was able to animate a fly-by sequence with my map so far...

Couldn't anybody be so kind ?

THX & bye.

I can give it a try tomorrow

Would be tremendous... Click to view attachment

Thought this might be fun, so I gave it a go, hope it's OK to post the results here.

Images rendered in Orbiter (graphics not as slick as Celestia, but does the job). Cassini vectors and orbital elements for Iapetus from JPL Horizons. Note: Horizons gives two different values for the radius of Iapetus, 718km or 734.5km - I use the latter.

Animation:
4.9Mb animated .gif (600 x 800), 1 frame per 100s simulation time, 30deg FOV (top to bottom), covers 3.5 hours from 20 mins before close approach

http://images.canoop.com/images/nkmmydaexmydmzxi5od5.gif

(download speed is a little slow, so you may find it easier to right-click link and "save target as" and view at your leisure)

Stills:
The .gif is not that clear in the later stages of flyby, so here's a few screenshots (600 x 600 .jpg)

http://img161.imageshack.us/img161/9579/cassiap1nw3.jpg

http://img515.imageshack.us/img515/7343/cassiap2we2.jpg

http://img161.imageshack.us/img161/5696/cassiap3ox7.jpg

http://img515.imageshack.us/img515/4346/cassiap4mz3.jpg

http://img507.imageshack.us/img507/2824/cassiap5ig6.jpg

http://img161.imageshack.us/img161/2382/cassiap6so3.jpg


Cheers.

Hi Brian,

many thanks for this nice work... Click to view attachment

Bye.

I'm sorry I was never able to get that done. Celestia kept crashing whenever I tried that map. I think it might have something to do with the fact that it isn't one of the standard sizes for the maps Celestia uses. Celestia is supposed to handle those now so I suspect this is another issue one could chalk up to my slow laptop.

Jason,
Any chance we could get a Kodak Moment as Saturn is rising over the edge of Iapetus? I noticed it during the animation, but I don't know what kind of footprint a WAC frame would make at that range.

ObFunny: At first, reading Belleraphon1's comment about "except they will have to put up with my tears and crying when I see a Saturn rise.....", I was thinking, "When did Cassini get a picture of that?!? Wait, it's an Apollo movie, maybe they took a picture of Saturn rising above the horizon...But the only photo I can think of is of Earth rising....Waitasec -*SMACK*- Duuuuuuuuuuhhhhhh. Sometimes I miss the glaringly obvious...

Hi once again,

as Titan 048TI (T34) Mission Description for July 19th has been published,
I'm wondering when such a paper will follow for Iapetus 049IA ?
Shouldn't be that far away...?

Bye.

There's an interesting little piece up today on the Cassini main website regarding the history of Iapetus. Short version: It asserts that the "belly band" is primordial and dates back 4.5 Gyr at least.

If this notion is borne out by the September flyby, it is going to have some *major* repercussions for the various theories regarding the "late heavy bombardment". Models that require a lot of chaos in the outer Solar System due to Jupiter/Saturn 2:1, or late formation of Uranus and Neptune, are going to have to explain how the bellyband managed to survive -- even in its current beat-up state -- with so much debris flying around out there.

It could provide an indirect boost to the Planet V hypothesis, I suppose. Process of elimination and all that.

Glad to see this was recently included for ISS imagery. Among other things, this should show the "face" region (see the "New Iapetian image series" thread) located at the lower right corner of the bottom green VIMS rectangle.

I hope to soon be able to post an updated full resolution Iapetus map along with Celestia view for this encounter.

Here's my updated Iapetus map at this URL that has images from July 8, 2007 and October 2004 added:

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

Here with the help of Celestia is my reckoning for how Iapetus will look to Cassini on September 12. Since it's the weekend I'll try and see if I can upload/attach this image directly...

Click to view attachment

What a massiv basin it really is - nearly a third of Iapetus diameter... Click to view attachment

I'll try attaching a quick Celestia movie if it can fit in the size limit...Click to view attachment

Here's a second version of the movie that focuses more on the closest approach...

Click to view attachment

EDIT:
I've made a longer version of the movie (3MB) as well at the link shown below. Celestia has the closest approach too far away at about 5000km, though at farther ranges the animation should be fairly realistic.

http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus9.avi

Some more informations about the September flyby :

http://www.cosis.net/abstracts/EPSC2007/00...076ebb8f800aea1

A SAR observation will be performed, the only one of an icy satellite.

Will it help to determine the thickness of the dark material (or reveal hidden structures) ?

Marc.

Wow !!

Perhaps we can characterize the surface roughness for a possible Iapetan rover someday with a SAR observation.

I would love to see a scan of Atlas too, maybe it would reveal new info on the accumulated ring materials.

A fast moving view covering the entire month before encounter, then some time afterwards...