“NASA scientists are on the trail of Iapetus’ mysterious dark side, which seems to be home to a bizarre “runaway” process that is transporting vaporized water ice from the dark areas to the white areas of the Saturnian moon.

This “thermal segregation” model may explain many details of the moon’s strange and dramatically two-toned appearance, which have been revealed exquisitely in images collected during a recent close flyby of Iapetus by NASA’s Cassini spacecraft.

Infrared observations from the flyby confirm that the dark material is warm enough (approximately minus 230 degrees Fahrenheit or 127 Kelvin) for very slow release of water vapor from water ice, and this process is probably a major factor in determining the distinct brightness boundaries.

“The side of Iapetus that faces forward in its orbit around Saturn is being darkened by some mysterious process,” said John Spencer, Cassini scientist with the composite infrared spectrometer team from the Southwest Research Institute, Boulder, Colo. ”

continues at:-

http://www.jpl.nasa.gov/news/news.cfm?release=2007-113

I find it difficult to discern between ice on a rocky surface and “soot”* on an icy surface. I could be persueded either way from these images, which does not provide conclusive evidence. Now the comments about fresh craters and the exposed white does seem more suggestive.

*I don’t think it is soot, but just provoking the imagery of soot on ice.

Would the dark area absorb sufficient energy to keep itself ice-free?

Does the dark side of Iapetus face toward or away from Saturn? (Effect of more incident sunlight?)

Could Iapetus have enough heat generated internally (Saturn squeezing it must cause some) to keep the surface partially ice-free? Perhaps the internal structure is non-uniform, so the energy output is also non-uniform. (Would mapping Iapetus for gravity distribution at surface confirm the internal structure?)

Quite a neat wee moon.

I am more interested in what further surprises Europa might have in store, though. A water-ice covered moon with an oxygen atmosphere (well, OK, tenuous atmosphere). Hmm.

I’ve studied the blown up image of Iapetus in detail and I can’t find anything that convinces me that the icy material isn’t overlying the dark matt material. If someone can convince me otherwise, I’d be happy to accept their arguments.

To me, the lighter areas, look very much like what happens when snow begins to melt. ie. patches of hardened icy-stuff persist and gradually pock-marks and holes develop.

If there is some dynamic melting process going on, couldn’t it be solved rather simply by observing the moon in detail over a few weeks?

Since there is evidence that it’s been something like this for centuries, I like the idea that Saturn’s causing it. Perhaps something to do with magnetic fields, or maybe it just radiates enough e-m? Isn’t it like Jupiter, a planet which emits more than it receive?

See the third panel in this photo series:
http://www.planetary.org/image/iapetus_voyagermountain_adjust-levels.jpg

By making the black part of Iapetus correctly exposed, and overexposing the light part, it can be seen that there are dark colored craters partly covered by white. It wouldn’t make sense to have a white base that was partly covered by a half crater.

I say the dark area of Iapetus is where the “snow” (or whatever it is) has been removed (or didn’t accumulate); perhaps by sublimation or some such process. If the dark side of Iapetus faces Saturn, maybe the Saturnshine or other radiation from Saturn has caused the removal of the white stuff from that side.

“BA, you have a strong voice thanks to your website and your reputation.
Please continue to use your strong voice to resist the ever-escalating war against reason that is being relentlessly waged by a handful of hyper-wealthy religious fanatics (and the hyper-wealthy who pretend to be religious).

I am an American.
I want my nation to remain the bastion of sanity and reason that it was created to be by our Founding Fathers, not the Puritan witch-hanging horror that a few among us are manipulating the rest of us to become.
Please keep defending us! Defend reason!

Defend science.”

Hear! Hear!

That goes I think for all rational people.

All too sadly, unless the nuttiness of religious nuts is pointed out clearly all too many people who don’t think clearly enough tend to fall for the religious nutters nuttiness. Well nuts to that!

If we are to have a positive future, the backward thinking, evil, regressive, intolerant, anti-choice (all choice too – not just women’s) , plain outright wrong religious nuts _need_ to be stopped from controlling everyone’s lives.

Americans (USA-ites, that is Cubans, Canadians, Peruvians, etc .. not included here) generally, seem unfathomably anti-intelligence and pro-Christian extremist which is utterly self-destructive and harmful for the entire planet not to mention a tragic waste of a nation with so much potential as well.

“…relativistic speeds…”
This is getting fun!

Whether this will be true with realistic speeds I will leave to professionals. ( That would be you. )

Great post BTW.

Giant picture of Iapetus = Cool!
Pointing out that religious nuts are…well…nuts (duh) = boring.

It’s your site, do what you want with it, but the lack of science is making my visits less frequent.”

BA, you have a strong voice thanks to your website and your reputation.
Please continue to use your strong voice to resist the ever-escalating war against reason that is being relentlessly waged by a handful of hyper-wealthy religious fanatics (and the hyper-wealthy who pretend to be religious).

I am an American.
I want my nation to remain the bastion of sanity and reason that it was created to be by our Founding Fathers, not the Puritan witch-hanging horror that a few among us are manipulating the rest of us to become.
Please keep defending us! Defend reason!

Defend science.

That amazing, half-a-world-wide “wall” trumps all the other strangeness of this moon, in my opinion.

“…only the total energy (or momentum, if you wanna do it that way) matters.”
Kinetic energy is not the same thing as momentum! I hope you’re being casual here.

Haleakala is also known for having a spectacular sunrise view which tourists have been watching for over a century (Mark Twain wrote of his experiences in “The Innocents Abroad”). I have seen it myself and it is worth the trouble. I got to see the edge of the earth’s shadow move through the faint haze in the sky, and I swear that I felt a “thump” when the shadow’s edge reached me and the limb of the sun crept over the horizon. Looking toward the west I got to see the shadow of Haleakala seem to converge to the other horizon. As a bonus while waiting for the sunrise, I got to see Alpha Centuri and Omega Centuri for the first time (although I didn’t have a pair of binocular with me–rats!).

If anyone reading this would like to see this phenomenon when they visit Maui, know that despite being in Hawaii the combination of the altitude and the wind-chill factor make it mandatory that you bring some wind protection if not actual cool weather gear. When I was there I wouldn’t be surprised if the pre-dawn temperature was around 50 degrees F and wind-chilled to under 40 degrees F (5 degrees Celsius). You also have to start your trip up the mountain quite early–2 or 3 am–or you won’t find a parking spot in the small lots near the summit, and you really don’t want to have too long a hike at the 10,000-foot altitude without some previous training.

As for whether the two craters are related, when the sample space is the whole ancient solid surface of the Solar System, getting two overlapping craters of similar size *somewhere* by chance doesn’t seem that much of a stretch. It’s going to seem dramatic at the moment of discovery, sure.

I’m pretty sure that you were right the first time. (But even with the ejected matter considered it was a pretty small nudge to Iapetus.) So please, go ahead with that back of envelope calculation and let us know what you find.

You know, I completely agree. If asked if Jupiter or Saturn would have the oddest features, Jupiter would have gotten my vote. They’re both pretty interesting, but Saturn is taking the cake.

The left hand crater seems deeper and sharper than the right, though they both show similar surface texture and smaller craters.

Harold said:
> Forgive my enormous ignorance, but by “double impact basin” are you referring to the feature that occupies the entire lower left quadrant of this image? The contours of the two basins seem very congruent, reminiscent of the way the East coast of South America fits into the West coast of Africa. Is it possible that there is some other, more direct relationship between these two features?

What other relationship do you propose? There does appear to be some similarity of the shapes.

Seen on posting a comment on the rather lame captcha.

To me, the dark areas don’t look like dust ejecta, but a material that is underlying a layer of water ice.
For instance, there are several dark craters with a central patch of ice and all the dark areas I can see have well defined edges.

It’s been suggested that polymerisation of ethane and methane by ultra violet radiation might be responsible the dark material.
Could it be that some kind of differential sublimation of ice is going occuring, which exposes it?

If so, why is it so pronounced one side of the moon?
(This been observed since Cassini’s observations (the person that is) in the 17th C)