What the h*** is this thing on Iapetus??

[Dick Jacobson]

Check out the bizarre ridge going around the equator of Saturn's moon Iapetus (see http://www.spaceflightnow.com/cassini/0 ... petus.html. This reminds me of the seam going around a molded foam-rubber ball. What could cause this??

One idea that occurred to me is that at some time in the past Saturn's rings were much larger than they are now, extending all the way out to Iapetus. As Iapetus orbited in the ring plane, material was deposited in a narrow ridge on its equator. Particles that were above or below the ring plane could explain the "sooty" areas on either side of the equator.

Any other ideas?

How many more surprises will we find during the next four years of Cassini's mission? There should be some more on Friday when Huygens enters the atmosphere of Titan.

This is what I love about astronomy, and science in general. Every time we think we understand things, something new and strange and totally unexpected pops up.

[SEmert]

Any other ideas?

I think Iapetus is actually a gigantic walnut. Wait until you see the size of the guy that comes along to crack it open!

Steve

[Bill Bynum]

Nah, Iapetus just has his mouth closed. Whaddaya want from a Titan, a grin?

(See his eyes? Gotta do something about that skin though...)

[Kirk]

It says the ridge is about 12 miles wide. How wide are Saturn's rings?

~Kirk

[Dick Jacobson]

Recent estimates that I've seen range from 1 kilometer to an amazingly thin 100 meters for Saturn's ring thickness. I suppose the material could accumulate in a thin band and then tumble down the sides of the ridge. In 2007 Cassini will get some pictures from 100 times closer, which should be really interesting! I predict that the "Iapetus Ridge" will be a prime target for rovers 50 or 100 years from now. If it's really a collapsed ring, it would be a treasure trove of primitive Solar System material.

Another possibility is that Iapetus once had its own rings, which somehow collapsed onto its equator. The trouble with this is that most of the material seems to be on one side instead of all the way around. More likely Iapetus was once a "shepherd moon" of a ring system, like the tiny shepherd moons in the present ring system. Maybe the mark of a retired shepherd is that you end up covered with soot and a bulging waistline!

[Dick Jacobson]

At last, a professional astronomer has come to the same conclusion that I did regarding that strange equatorial ridge (or "belly band") on Iapetus. See http://www.newscientist.com/article.ns? ... 624995.600. (Paulo, you thief, have you been reading the MAS web site??)

Radio astronomer Paulo Freire claims that this ridge formed when Iapetus orbited at the edge of a ring of Saturn. The main problem with this theory is that Iapetus' orbit now is far outside of Saturn's rings and is not even in the same plane. But maybe in the early, unruly days of the Solar System, some other body approached Iapetus and yanked it out of its orbit. This other body could be Saturn's outermost large moon Phoebe, which is now believed to be a captured Kuiper Belt object.

Too bad we don't have a copy of Encyclopaedia Galactica; it probably has some exciting videos of the early days of the Solar system.

[Starforce2]

wouldn't they be able to measure the orbit and backtrack it? They've done it before.

[Deane Clark]

Two words:

Death Star