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SYFY WIRE Bad Astronomy

Cassini Spies a Forbidden Planet’s Flying Saucer Moon

By Phil Plait

The Cassini spacecraft orbiting Saturn has taken a picture of a flying-saucer-shaped object using a force field to manipulate one of the planetâs rings.

Yes, I know what today is! But I assure you, this picture is quite real:

The object is Saturnâs moon Prometheus, a chunk of ice about 136 kilometers (85 miles) long. It orbits Saturn near the planetâs narrow F ring, and thatâs no coincidence. Prometheus and its sister moon Pandora flank the ring (Prometheus on the insideâtoward Saturnâand Pandora on the outer side), and the force of their gravity helps constrain the tight path of the ring particles. For this reason theyâre called shepherd moons.

This picture threw me for a moment. Prometheus is elongated and potato-shaped, while Pandora is somewhat squatter. In some pictures Pandora is the one that looks like a flying saucer, but the angle of the sunlight here gives Prometheus a decidedly alien spaceshipy look. It looks very much like an April Fools' Day picture just posted by International Space Station Commander Chris Hadfield, too.

In fact, this looks so much like the United Planets Cruiser C57-Dâon today of all daysâ I had to make sure this picture was real. As far as I can tell, it is. Thatâs good! After all, I wouldnât want to create a Tempest in a teapot.

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