A research team at Cornell University, headed by Daniel Tamayo, has come up with a new model for why Saturn's moon Iapetus has a dark side and a light side. Not a dark side and a light side like the moon, which is differentially colored only because of differential lighting, but a dark side and a light side because of true albedo, or reflectiveness.

Iapetus. Ee-ah-pet-us. Credit: NASA/JPL/Space Science Institute

While Cassini , the original Saturn scientist, thought that the moon was dark-light because it was tidally locked, like the moon, meaning that only one side ever faced the planet, which is true, that is not the full explanation.

The full explanation involves, like most important astronomical topics (such as star formation and galaxies' shapes), dust. Dust, in astronomical terms, just means solid particles, not (necessarily) dead skin flakes, like it does here on Earth.

While astronomers have long thought that another of Saturn's moons, Phoebe, was depositing dust onto Iapetus, Tamayo, et al., have shown that Saturn's other, darker irregular satellites are making some deposits of their own.

Anyway, the point is, these are the kinds of questions that occur to astronomers. You start with "Does this moon look like our moon?" and then you go, "Yes. But does it look that way for the same reason."

"Maybe. I'm not sure. What if different parts are made of different material?"

"Why would different parts have different composition?"

"Maybe there's some process that occurs on one side that doesn't occur on the other?"

"That only makes sense if the process is driven by something outside the moon. Maybe it's driven by another moon?"

"Maybe it's driven by the other moonz? Plural?"

It's a journey, yo.

Check out the summary at UniverseToday or the original paper on the arXiv. The original paper includes a history of astronomers' thoughts regarding Iapetus's dichotomous halves.



Daniel Tamayo, Joseph A. Burns, Douglas P. Hamilton, & Matthew M. Hedman (2011). Finding the trigger to Iapetus' odd global albedo pattern: Dynamics of

dust from Saturn's irregular satellites Icarus arXiv: 1106.1893v1