[meteorite-list] Saturn's Spokes: Spawned by Storms?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 19 Apr 2007 16:02:26 -0700 (PDT)
Message-ID: <200704192302.l3JN2Qo15970_at_zagami.jpl.nasa.gov>

http://sciencenow.sciencemag.org/cgi/content/full/2007/419/1

Saturn's Spokes: Spawned by Storms?
By Govert Schilling
ScienceNOW Daily News
19 April 2007

PRESTON, U.K.--Dark, radial spokes in the rings of Saturn have puzzled
planetary astronomers ever since they were discovered by the Voyager
spacecraft in the early 1980's. Today, at the Royal Astronomical Society
National Astronomy Meeting here, scientists described how the enigmatic
features could be caused by thunderstorms and lightning. "It's one of
the best theories I've heard so far," says Carl Murray of Queen Mary
University of London.

The spokes are clouds of electrostatically charged dust particles that
float above and below the ring plane. But there's no consensus on how
they form. Astronomers have suggested that meteorite impacts or solar
wind particles may do the charging, but no single theory has been able
to explain all the observed characteristics of the spokes, such as their
locations, shapes, clustering behavior, and--most notably--their
puzzling absence between October 1998 and September 2005.

Enter the thunderstorm model, proposed by Geraint Jones of the Mullard
Space Science Laboratory in Dorking, U.K., and colleagues, and presented
at the meeting by team member Christopher Arridge. According to this
idea, energetic beams of electrons produced above these storms are
transported to the rings by Saturn's magnetic field, where they charge
the dust and lift it out of the ring plane. If the storms occur at
approximately 43 degrees latitude north or south, the electrons end up
in a part of the ring that rotates at the same speed as the planet, so
spokes can build up. Their absence between 1998 and 2005--about one
quarter of a Saturnian year--may be just a seasonal effect in the
occurrence of thunderstorms at this particular latitude, the astronomers
speculate.

The thunderstorm model nicely explains why spokes occur in groups, says
spoke expert Colin Mitchell of the Space Science Institute in Boulder,
Colorado. But, he says, it doesn't account for the very narrow spokes
that are also observed. "Spokes seem to be a pretty complicated
problem," says Mitchell. "We definitely don't have the final word yet."
Confirmation could come from NASA's Cassini probe, which is orbiting
Saturn. If a thunderstorm is seen at the same time and the right
location, Mitchell says, "that would be an indicator that the model is a
good starting point."
Received on Thu 19 Apr 2007 07:02:26 PM PDT