Web edition: October 31, 2011
There are four – count ‘em! –moons in this photograph taken September 17 by the Cassini spacecraft, which has been orbiting Saturn since 2004. Can you find all of them?
Saturn’s enormous moon Titan lurks in the background, a shadowy sphere 5,150 kilometers in diameter with a darkened north pole. Leaping out in front of murky Titan is Dione, about a third as bigacross as Earth’s moon with bright, icy fingers forking across its trailing hemisphere. Near the edge of the rings on the right is Pandora, a tiny shepherd moon just 81 kilometers wide that helps keep Saturn’s F ring in line.
And embedded in the A ring, near the left of the image, is Pan – the runt of the moony quartet at just 28 kilometers across and a vacuum cleaner for the ring’s Encke Gap, where it resides. As house-keeping Pan orbits Saturn, it keeps the gap clear of ring particles either by munching them, kicking them in toward the planet or booting them from the system.
Saturn’s rings, though looming large and iconic from most angles, are nearly invisible if viewed edge-on. Scientists estimate the rings are only 10 meters thick – most city buses are longer.