Emily Lakdawalla • Oct 21, 2009
Spinning spokes in Saturn's rings
Here's a neat animation captured last month by Cassini and assembled by Mike Malaska: spokes in Saturn's B ring. The spokes are especially prominent just now, so close to equinox.
Spokes were first observed by the Voyagers nearly 30 years ago, when Saturn happened to be in the same season it is now:
Hubble continued to observe them until 1998. They consist of tiny particles levitated above the ring plane by electrostatic forces; it's not clear if the angle of incoming sunlight has a role to play in the production of spokes, or if it merely takes low-angle spring and autumn sunlight to make the spokes visible. Recently it was suggested that they are connected to thunderstorms in Saturn's atmosphere. Cassini first spied spokes in September 2005, and over its extended (and hopefully extended-extended) mission it'll continue to watch them (probably) fade back into invisibility.
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