APOD: 2021 July 13 - Saturns Iapetus: Painted Moon in 3D

Good morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Saturn's Iapetus: Painted Moon in 3D." This is a fun visualization of data collected in 2007 by the Cassini space probe. Move your mouse to either the left or right of Iapetus and hit one of your arrow keys (the moon will spin on the corresponding axis). Similarly, grab and hold the image of Iapetus with your mouse, and you can spin it like a globe.

Iapetus was discovered by Giovanni Domenico Cassini, an Italian-born French astronomer, in October 1671. The moon is tidally locked, meaning it keeps the same face towards Saturn during the course of its 79-day orbit. Researchers are unsure of what gives Iapetus its 'painted moon' moniker. Its low density suggests that the moon is mostly water ice with some rocky material. One theory is that water ice sublimates (evaporates) on the dark region, leaving the rocky residue on the surface. Over geologic time, this would result in a buildup of ice in the lighter hemisphere, where differences in reflectivity (e.g. albedo) might establish a thermal feedback loop between the two surfaces. But something else would be necessary to start this process in the first place...in 2009, the Spitzer Space Telescope detected a dust ring just inside the orbit of the largest of Saturn's outer moons, Phoebe. This debris is outside the orbit of Iapetus, and would spiral in as its orbit decays. A portion of this material would have been swept up by the leading hemisphere of a tidally-locked moon, setting the thermal feedback loop in motion. It's fun to see how the puzzle might fit together, isn't it?