[cassini] Iapetus

[symaski62]

http://photojournal.jpl.nasa.gov/jpeg/PIA06145.jpg

Original Caption Released with Image:

These spectacular Cassini images of Saturn's moon Iapetus show an enticing world of contrasts.

These are the sharpest views of Iapetus from Cassini so far, and they represent better resolution than the best images of this moon achieved by NASA's Voyager spacecraft. Images obtained using ultraviolet (centered at 338 nanometers), green (568 nanometers) and infrared (930 nanometers) filters were combined to produce the enhanced color views at left and center; the image at the right was obtained in visible white light. The images on the bottom row are identical to those on top, with the addition of an overlying coordinate grid.

These views show parts of the moon's anti-Saturn side--the side that faces away from the ringed planet--which will not be imaged again by Cassini until Sept., 2007. In the central view, part of the moon's eastern edge was not imaged and appears to be cut off.

With a diameter of 1,436 kilometers (892 miles), Iapetus is Saturn's third largest moon. It is famous for the dramatic contrasts in brightness on its surface--the leading hemisphere is as dark as a freshly-tarred street, and the trailing hemisphere and poles almost as bright as snow.

Many impact craters can be seen in the bright terrain and in the transition zone between bright and dark, and for the first time in parts of the dark terrain. Also visible is a line of mountains that appear as a string of bright dots in the two color images at left, and on the eastern limb in the image at right. These mountains were originally detected in Voyager images, and might compete in height with the tallest mountains on Earth, Jupiter's moon Io and possibly even Mars. Further observations will be required to precisely determine their heights. Interestingly, the line of peaks is aligned remarkably close to the equator of Iapetus.

The large circular feature rotating into view in the southern hemisphere is probably an impact structure with a diameter of more than 400 kilometers (250 miles), and was first seen in low-resolution Cassini images just two months earlier.

Theses images were taken with the Cassini spacecraft narrow angle camera between Oct, 15 and 20, 2004, at distances of 1.2, 1.1 and 1.3 million kilometers (746,000, 684,000 and 808,000 miles) from Iapetus, respectively. The Sun-Iapetus-spacecraft, or phase, angle changes from 88 to 144 degrees across the three images. The image scale is approximately 7 kilometers (4.5 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras, were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information, about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.



Image Credit:
NASA/JPL/Space Science Institute

[lostfisherman]

Nice picture

They are to try out further attempts at imaging Iapetus using Saturn shine, according to this

http://saturn1.jpl.nasa.gov/cgi-bin/gs2 ... type=image

I must admit to Iapetus being my favourite place, I'm looking forward to January 1st, when Cassini gets closer than ever.

[Matt McIrvin]

Here is a raw picture from two days ago that I enhanced a bit:



It looks as if that line of gigantic mountains just keeps running along the equator, right across the dark oval. Look at how tall they are on the horizon!

I'm looking forward to the next few days... Iapetus just looks weirder and weirder.

[julesstoop]

Probably has something to do with that huge crater on the left.

[Matt McIrvin]

I also found this very nice 1939 Astounding Science Fiction cover showing a view of Saturn from Iapetus (I can't find the name of the collector, unfortunately). The artist, Charles Schneeman, really did his homework-- I'd say it stands up pretty well even today! The foreground landscape seems a subtle homage to Iapetus's two-tone color, though it remains to be seen whether there's anything like those Alpine crags.

[Brendan]

I use 3ds models for Mimas and Tethys. Whoever made those should make one for Iapetus when the data is available.

Brendan

[Matt McIrvin]

I use 3ds models for Mimas and Tethys. Whoever made those should make one for Iapetus when the data is available. 8O

Brendan

That might be a long time in coming! Personally, I'd be satisfied by a higher-resolution map. But moon cartography takes time...

[jestr]

If anyone wants to make a map,I'm sure I could have a stab at making a model,but its probably better to wait til we get some more images of Iapetus,Jestr

[Matt McIrvin]

Yes, I'd be inclined to wait until the people who do this stuff for a living put out a map. They've got the best software, the best data and the best knowledge about how to put it all together.

(In the meantime, the Planetary Society Saturn site has Voyager-based photomosaics that are interesting alternatives to the USGS maps.)

[Matt McIrvin]

There are slightly better raw images now, from which I made a false-color picture (IR/green/UV):



But I'm sure I'm only half a step ahead of the pros...

[chris]

A more detailed picture of the equatorial ridge on Iapetus:

http://saturn.jpl.nasa.gov/multimedia/i ... 026247.jpg

I'm completely puzzled as to what it is, or whether it's merely coincidence that it's aligned with the equator.

--Chris

[lostfisherman]

...yeah, it's as if the place has a spine
http://saturn1.jpl.nasa.gov/multimedia/ ... geID=29492

[Matt McIrvin]

Here's a mosaic of the most recent Cassini raw images showing the whole illuminated disk:

http://world.std.com/~mmcirvin/iapetus_mosaic.jpg

I'm no geologist, but in appearance, the spine reminds me of nothing so much as Earth's mid-ocean ridges, which come from sea-floor spreading at plate boundaries. But could an analogous process have gone on there? And the fact that it's exactly on the equator and runs right down the middle of the dark oval... is this a coincidence or not? No idea.

[Dollan]

Yes, it DOES seem to be in the middle of the dark region, doesn't it? It looks to me almost as if two hemispheres have been squashed together, or if the moon was squeezed somehow. I wonder if it is of internal geological origin. If so, and if it does stick to the rough center of the dark region, I would almost bet that it indeed the *origin* of the dark material.

Or, it could be something totally different. It also reminds me of those plastic eggs that silly Putty comes in. Hmmm.... **chortles**

...John...

[jim]

Here's a mosaic of the most recent Cassini raw images showing the whole illuminated disk:

http://world.std.com/~mmcirvin/iapetus_mosaic.jpg

I'm no geologist, but in appearance, the spine reminds me of nothing so much as Earth's mid-ocean ridges, which come from sea-floor spreading at plate boundaries. But could an analogous process have gone on there? And the fact that it's exactly on the equator and runs right down the middle of the dark oval... is this a coincidence or not? No idea.

Hehe This is my version of the mosaic.



link to highres picture ( 340 kB )
http://www.webhosting4free.org/jimpage/ ... _cass2.jpg

Bye Jens

--------------
Happy new year!

[maxim]

I'm no geologist, but in appearance, the spine reminds me of nothing so much as Earth's mid-ocean ridges, which come from sea-floor spreading at plate boundaries. But could an analogous process have gone on there?

There is shurely no (present) plate tectonics on iapetus.

I wonder if it is of internal geological origin.

The picture is not very clear, but looking at all the small crater edges it seems that they are not interrupting, but following the ridges shape. That means that the craters are older than the ridge - which means that the ridge is geologically quite young and obviously created by some kind of internal folding process. I know of no information about the internal structure of Iapetus, so this phenomenon stays unanswered.

maxim

[Matt McIrvin]

Hehe :D This is my version of the mosaic. ;-)

Nice one! This is the first version I've seen that mosaiced the whole disk as UV/green/IR color. (They actually took visible-light RGB exposures of all these pictures too. Out of curiosity I tried making a close-to-true-color picture of one of the shots, only to find that in visible light Iapetus really doesn't have any color; it just looked like the B&W photo.)

There are a bunch of closer pictures from later in the flyby up now, including some of the Saturn-light nightside pictures. But the JPEG conversion of JPL's raw image archive knocked out enough of the dynamic range of those to make them hard to use; we might have to wait for the imaging team to release really good Saturn-light composites.

[jestr]

Theres a bunch of new images on the Ciclops site now
http://ciclops.lpl.arizona.edu/view_event.php?id=9
and also on the JPL site.It looks to me like there are numerous craters along the big ridge as well.Does anyone think that two roughly similar sized moons could have collided in the past to form Iapetus-I know a few asteroids are formed this way,could this account for the 2-tone appearance and the ridge?Jestr

[Darkshot]

Heh, the more I look at Iapetus, the more I think it looks like the Death Star, now it even has what looks like a trench! This planet might even be more interesting then Titan. MIGHT...

[Scorpiove]

I think Mimas looks more like the death star though .