PDA

View Full Version : Explanation for Iapetus



Swift
2011-Jul-14, 04:48 PM
From Science News (http://www.sciencenews.org/view/generic/id/332324/title/Iapetus_gets_dusted)

Imagine a powdered sugar doughnut hole plowing through a cloud of dark-chocolate dust. The resulting two-colored treat would resemble one of Saturnís weirder moons, Iapetus ó an icy world with a coal-black face and a bright white backside.

For centuries astronomers have puzzled over the source of this yin-yang color pattern. Now a team led by graduate student Daniel Tamayo of Cornell offers an explanation: Dust flung from another one of Saturnís moons is coating one side of Iapetus. Because Iapetus doesnít rotate with respect to Saturn, the same face continually catches the dark moon flakes.

The study is apparently published in the online July 7 issue of Icarus.

Buttercup
2011-Jul-14, 05:59 PM
I thought a similar article/finding was published months ago. :confused: This isn't news to me.

mantiss
2011-Jul-14, 06:33 PM
I am surprised as well, this was well known for a year and I am tempted to even say years. Perhaps this paper goes a step deeper by computing the actual details of the stuff flown off Phoebe and cascading down to Iapetus, but the source I believe has been suspected for a very long time, long enough to enter the general consensus even if the finer details weren't worked out.

Jerry
2011-Jul-17, 11:18 AM
The moon is basically dark, with a light coating of co2 and water ice - same ice found in saturns rings and spray-painting from Enceladus.

When the moon locked in sync with Saturn, the leading hemisphere started experiencing more hits from comet and meteor debris - vaporizing the volatiles on the leading hemisphere, and reexposing the dark interior. To speculate that Phoebe is chunking out dark stuff: Why would it be selectively pummeling Iapetus?

This explanation works as well as the other, and is more consistent with dirty debris we find in comets that we have examined.

Why is Enceladus a spray-paint can? That is a great question.

mantiss
2011-Jul-17, 01:29 PM
To speculate that Phoebe is chunking out dark stuff: Why would it be selectively pummeling Iapetus?

Celestial mechanics, and the fact that Iapetus is the next moon inwards after Phoebe so it's scooping the freshest stream, after that it's going to be Titan and I expect that all the volatile debris would wash down into the muck of ethane/methane in its atmosphere. There's also tiny Hyperion in between the two and you'll notice that the bottom of craters is filled with dark material, some speculate that differential heating of darker material led to the pitted appearance of Hyperion. It works in My book :)

Middenrat
2011-Jul-18, 01:23 AM
Two convincing theories, I would like to ask Jerry where are the other examples of dichromatic moons you might expect that process to throw up.

ravens_cry
2011-Jul-18, 07:36 AM
So Iaptus is a cosmic Timbit?
Neat. It certainly is one of those curiosities about our solar system.

tusenfem
2011-Jul-18, 09:33 AM
When the moon locked in sync with Saturn, the leading hemisphere started experiencing more hits from comet and meteor debris - vaporizing the volatiles on the leading hemisphere, and reexposing the dark interior.


However, it does not work that way, as the moon will orbit Saturn slower that then 10 hour rotation period of the planet, and thus the magnetospheric plasma will weather the trailing side of the moon, just like e.g. Europa.

johnsmith22
2011-Jul-25, 12:16 PM
The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 20-kilometer wide (12 miles) band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 13 kilometers (8 miles) above the surrounding terrain. Along the roughly 1,300 kilometer (800 mile) length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained. It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge.


_______________
Cegonsoft (http://econnect.entrepreneur.com/Cegonsoft8760/)