An
invisible donut of trapped, hot particles surrounding Saturn is all bent out of
shape--a finding that astronomers can't yet explain.
A similar
"ring current" phenomenon occurs around Earth as a relatively stable
donut when present, but new Cassini spacecraft images show Saturn's loop is a
lopsided mess.
"It's
curious that Saturn's ring current isn't symmetric," said Don Mitchell, an
astrophysicist at Johns Hopkins University who helped examine the images beamed
back to Earth. "We think the solar wind is squishing the sunward side of
the ring current, kind of like a wind sock."
Planets
with magnetic fields can trap hot particles within their clutches to form giant
electrified clouds—the ring currents—that are invisible to the naked eye.
Earth's
ring current is made of hydrogen and appears during
solar flares. Saturn's is made largely of oxygen and is always present. The
saturnian moon Enceladus is responsible for the electric halo, as it
consistently spews
water vapor from its depths to feed the ring current with oxygen and
hydrogen ions.
Because
oxygen is far heavier than hydrogen, Mitchell said, Saturn's ring current can
distort the planet's magnetic field and make for an odd shape.
"The
heavier oxygen is like a rock on a string, stretching the magnetic field of
Saturn," Mitchell said.
More
mysterious to Mitchell and his colleagues, however, is a "clump" of
electrified particles within the ring that rotates in
sync with the planet roughly every 10 hours and 47 minutes.
Cassini's
images show the bright clump orbits Saturn between 300,000 and 634,000 miles
(485,000 and 1,000,000 kilometers) away from the planet's surface, but
astronomers have not yet figured out what creates it nor why it moves so quickly.
"Saturn
is a big fast rotator. The clump seems loosely hooked to the planet, yet
rotates with it," Mitchell said. "It may be connected with Saturn's
ring current, but we just don't know. This is something we're working very hard
to figure out."
Stamatios
Krimigis, also an astrophsycist at Johns Hopkins who examined the images, is
presenting them Thursday at the European Planetary Science Congress in Potsdam, Germany.
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