Strange Equatorial Feature on Iapetus

If you have ever been the Equator, you probably noticed that there was not much to notice. Unless, like the Mitad del Mundo in Ecuador, someone put up a monument, there is nothing to see.

Well, that appears not to be true for Iapetus. The recent images from the pre-Christmas Cassini pass by Iapetus showed a 20 km high ridge that follows the equator at least through the "dark" hemisphere.

This image shows the ridge line in profile :

while this image



(the ridge is harder to see in this image, but it starts in the lower left center and angles up and to the right towards the large crater at the top).

What are we to make about this ? One way to form long ridges is by compression - as is the case for the wrinkle ridges found in the older calderas of Olympus Mons. It's hard to see, though, why this should be equatorial in nature.

I have a gut feeling that this equatorial ridge and the light - dark division on Iapetus are related. I can't think of a good reason why, except that two independent strange global features on one small moon seems less likely than one strange event causing both. I am sure that we hear more of this; unfortunately the next close Iapetus pass isn't until 2007.

Only two days to the Huygens landing (spashdown ?). My fingers are crossed!