Approaching Iapetus - what makes it two-faced?

[alexblackwell]

<i>Guesses, anybody? ;-) Also, does anybody have any guesses about what new mysteries may be revealed? You've got just a few days before Cassini starts its closest study yet of the enigmatic moon, although I have no doubt that the mystery will linger for a long time to come.</i><br /><br />Some new Iapetus approach opnavs began hitting the ground yesterday, and the mystery deepens. See some of these processed images and discussion in Doug Ellison's Mars Exploration Rover Forum beginning on page 5 of a thread entitled "Iapetus Encounter In January."<br /><br />For review, below is the text from a slide in the Imaging Science Subsystem (ISS) presentation to the Cassini Satellites Orbiter Science Team (SOST) at the Iapetus B/C flyby preview meeting on December 20, 2004:<br /><br />=======================================<br /><br />About the [Iapetus] Albedo-Dichotomy Origin (table taken from [Tillman Denk's] DPS 2004 talk)<br /><br />Possible classification of Iapetus global albedo dichotomy origin hypotheses:<br /><br />1. Exogenic origin/ dust is coming in over long time<br /><br />(a) Dark grayish dust from Phoebe hits Iapetus's leading side and gets chemically altered/ reddened (Soter 1974, Burns et al. 1979, 1996; Hamilton 1997)<br /><br />(b) Dark reddish dust from smaller retrograde outer saturnian satellites covers Iapetus's leading side (Buratti et al. 2002)<br /><br />2. Asymmetric exogenic influence removes thin ice veneer from leading side, but not from trailing side and poles<br /><br />(a) Viewpoint of orbit mechanics:<br /><br />(a1) Circumsaturnian dust is the cause (from Phoebe or other outer Saturnian satellites)(Cruikshank et al. 1983; Bell et al. 1985; Buratti and Mosher 1995)<br /><br />(a2) Interplanetary micrometeoroid flux is the cause (Cook and Franklin 1970; Squyres and Sagan 1983; Wilson and Sagan 1996)<br /><br />(b) Viewpoint of physical processes on the surface:<br /><br />(b1) Exposing of the

 

[bobvanx]

Well, I guess that covers just about all the guesses.<br /><br />Oh, wait, except for:<br /><br />The residents of Titan greatly value the crystals that grow on Iapetus. For religious reasons, only those found on the leading side are taken. After several hundred years of surface mining, they reached the dark subsurface. Their civilization collapsed a millenia ago since they couldn't adapt to life without the Iapetus crystals.

 

[kelle]

If you look closely you can see a huge black monolith in the center of the light part of the moon. Hmm... what could it be. Maybe some kind of interdimensional and intergalactic travelling system?

 

[alexblackwell]

PIA06145: Waning Iapetus

 

[CalliArcale]

It's rather eerie (and of course Arthur C Clarke delights in recounting this) that in his book "2001", the monolith is placed right at the center of the trailing hemisphere of Iapetus -- where there does happen to be a rather dark crater. He described it as the "eye of Iapetus", which "blinks" when it lets Dave in.<br /><br />In some respects, it's a real pity that the movie had to switch the location to Jupiter. This was done primarily because the effects team just couldn't produce a satisfactory Saturn. The rings weren't coming out right. But Jupiter was no problem. On the other hand, it made for an interesting hook for the next few books -- Jupiter is considerably more massive than Saturn, and thus a better candidate for starhood. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[alexblackwell]

Iapetus B/C Flyby Animation

 

[grooble]

Have you got pictures of this monolith and ruins of the civilisation?

 

[alexblackwell]

<i>Have you got pictures of this monolith and ruins of the civili[z]ation?</i><br /><br />Is there any particular reason you posted the above in reply to <i>my</i> post?

 

[CalliArcale]

Presumably because you posted the link to that LOVELY animation, and he felt like making a jest on the subject of fictional monoliths. <img src="/images/icons/wink.gif" /><br /><br />I thought it was funny, but then, my sense of humor has been a bit whacked today.... <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[larper]

Hmm. The leading edge is darker, you say? My guess is miller moths, like on your car windshield.<br /><br />Maybe it just ran out of washer fluid. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[newtonian]

My, there are many guesses!<br /><br />I kind of like the removal of ice on one side and or deposition on the other side.<br /><br />What is the chemical composition and temperature?

 

[alexblackwell]

PIA06165: Iapetus' New Year's Flyby<br />December 30, 2004

 

[alexblackwell]

Cassini Caps off 2004 With Flyby of Icy Moon Iapetus<br />Jet Propulsion Laboratory<br />December 30, 2004

 

[odysseus145]

If the dark side were a hydrocarbon sea, I do not believe we would see craters on it. <div class="Discussion_UserSignature"> </div>

 

[alexblackwell]

The ISS hires imagery has already started hitting the ground. Here is a mosaic made by Doug Ellison, moderator of the Mars Exploration Rover Forum.

 

[alexblackwell]

<i>If the dark side were a hydrocarbon sea, I do not believe we would see craters on it.</i><br /><br />It's refreshing to see common sense rear its head from time to time ;-)

 

[odysseus145]

Just doing what I can <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[alexblackwell]

Cassini Images Iapetus<br />by Emily Lakdawalla<br />The Planetary Society<br />January 1, 2005

 

[bobvanx]

Wow, where did that equatorial ridge come from!?<br /><br />Is it possible that it's a record of sweeping up ring debris?

 

[bobvanx]

I grabbed this pic of Iapetus.<br /><br />The ridge is globe-encircling. You might recall that we saw it on the anti-Saturn side as well, as an odd, equatorial mountain range.<br /><br />Thanks claywoman, dunno what was wrong, but it works now.<br />

 

[claywoman]

Bobvanx,<br /><br />I clicked on your link and its not there any longer, at least that's the message I got...<br /><br />the ridge reminds me of what is on a walnut right where you hit it to split the shell...strange!!!

 

[CalliArcale]

I'm all sleepy from a cold, but logged on briefly anyway to look at Iapetus imagery....<br /><br />The first phrase that came out of my mouth on that picture was "Holy wow!" That ridge is bizarre -- in many ways, as bizarre as the stark albedo contrasts between the leading side and the trailing side. I've also been looking at the amazing craters. There are SEVERAL whoppers. It's amazing. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[silylene old]

Obviously the circumferential ridge (which seems to actually be a <i>double ridge</i> with a valley in the middle of it) is the seam where the two hollow halves were imperfectly glued together. Ever see a racquet ball or a tennis ball split in two due to a defect in the seam?<br /><br />*remembers that silly hollow planet thread, before the forums wipe*<br /><br />just kidding of course! <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[bobvanx]

claywoman, Calli, and silylene,<br /><br />Racquetball world aside, Iapetus also appears to be non-spherical. The equatorial, ridged dimension looks like it is several percent larger than the polar circumference. I don't really know, since these images haven't been corrected and callibrated, yet.<br /><br />But if it turns out that the dark stuff is ring debris, built up into a layer several kilometers thick, and the ridge is where the most stuff landed, that would really be something! Look at its orbit, it's big! If there had been a ring all the way out there, that would have been a giant!

 

[alexblackwell]

<i>Obviously the circumferential ridge (which seems to actually be a double ridge with a valley in the middle of it) is the seam where the two hollow halves were imperfectly glued together.</i><br /><br />Shades of the cracks and ridges on Europa.