The Light of a Distant Sun

A crescent Iapetus

Since I haven’t posted in a while, I thought I’d put up this image I was playing with last week…it’s a raw image of Saturn’s moon Iapetus combined with a bit of a “glow” from an off-frame Sun and a few stars thrown into the background. Just for curiosity’s sake. 🙂

914-mile-wide Iapetus was discovered in 1671 by Giovanni Cassini, who correctly deduced that the moon has a light side and a dark side when he noticed that the tidally-locked moon could only be seen when on the western side of Saturn. The contrast comes from a coating of darker material on the icy moon’s leading hemisphere, probably ejected off the more distant moon Phoebe, which causes that half to heat up quicker than the other and sending sublimed water vapor to the opposite side, where it refreezes. The dark side, having lost its icy particles, thus becomes darker and the bright side gets brighter, keeping the whole process moving along…a positive-feedback loop.

Raw image credit: NASA/JPL/SSI.