Stories tagged Iapetus

Sep
10
2007

Iapetus: This Cassini spacecraft view shows how the bright and dark regions on Iapetus fit together like the seams of a baseball.  Image courtesy NASA/JPL/Space Science Institute.
Iapetus: This Cassini spacecraft view shows how the bright and dark regions on Iapetus fit together like the seams of a baseball. Image courtesy NASA/JPL/Space Science Institute.
There are copies of Science News in my area of cube-land here at the Science Museum by the box of interoffice envelopes. The cover of the August 18 issue caught my attention – “Oddball Iapetus”. The title of the cover story is even better, “Idiosyncratic Iapetus”. Nice alliteration.

And, yeah, Iapetus is weird. Beyond the fact that in Greek mythology, Iapetus is the Titan son of Uranus and a moon of Saturn (you’d think that Iapetus would be a moon of Uranus) it is oddly colored and oddly shaped.

The moon is two-toned, and the reason for this is not exactly known. The darker surface might have been caused by any number of things – it could have even come from one of Saturn’s other moons. Some theorize that micrometer impacts on the moon Phoebe or Titan knocked the material loose and it was then swept up by Iapetus. Or perhaps when the cosmic collision that created the moon Hyperion occurred it produced debris that ended up covering part of Iapetus. Or if not from another source, the odd color could originate from within Iapetus, brought to the surface by meteor impact and/or cryovolcanism.

Iapetus is shaped sort of like a walnut, and even has an equatorial ridge that heightens the impression. Portions of this ridge rise more than 12 miles over the surrounding area. This shape is not totally unusual, but it is usually attributed to moons or planets that have a rapid rotation – but Iapetus has a very slow rotation (one rotation every 79 days) so how did this odd shape come about in this instance? The current theory is that at one point during Iapetus’ life, it had a much faster rotation, and about the same time it began to slow down its crust cooled and thickened, preserving the shape from its youth to today. (I am vastly simplifying things – for a complete account of how this is possible check out this article.)

AND what is way-copasetic and that I didn’t know until I started writing this blog, was that the Cassini spacecraft performs its closest flyby of its entire mission of Iapetus, TODAY, passing by about 1,000 miles of the moon – the closest any spacecraft has come to Iapetus. Read more about that here.