Explanation:
What causes the mysterious spokes in Saturn's rings?
Visible in the
above image
as light ghostlike impressions, spokes were first discovered by the
Voyager spacecraft
that buzzed by Saturn in the early 1980s.
Their existence was unexpected.
Oddly, the spokes are more commonly observed when Saturn's rings are more nearly edge on to the Sun, and so were conspicuously
absent from initial images sent back by the
robot Cassini spacecraft now orbiting Saturn.
Analyses of archived
Voyager images have led to the
conclusions that the transient spokes, which may form and dissipate over a few hours, are composed of electrically charged sheets of small dust-sized particles.
Hypotheses for spoke creation include small meteors impacting the rings and
electron beams from Saturnian atmospheric
lightning
spraying the rings.
As Saturn approaches equinox,
spoke sightings like that
pictured above are becoming increasingly common, giving planetary scientists fresh images and data with which to test origin hypotheses.
Free Lecture:
An APOD editor will review great space images this Friday in Kalamazoo, Michigan.
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