Homer
Simpson, meet your match in space: Astronomers have confirmed the existence of
a lopsided "doughnut" of electrified plasma surrounding Saturn.
The giant
ring current, as the doughnut is called, was confirmed following analysis of recent
Cassini spacecraft data. But the new information adds a twist to the electric
phenomenon, which extends more than 746,000 miles (1.2 million kilometers) into
space: It rotates.
Don
Mitchell, an astrophysicist at Johns Hopkins University and co-author of a new
study detailed in the Dec. 13 issue of the journal Nature, revealed his
team's initial findings at a conference earlier
this year, but said the new study now confirms them. He explained that most
of Saturn's ring current plasma comes from its ice-spewing moon Enceladus.
"Earth's
ring current is made of upper atmosphere and solar wind particles, so it's
mostly hydrogen," Mitchell said. "But Saturn's source is by and large
Enceladus, which shoots out a whole lot of oxygen in the form of water."
Mitchell
explained that sunlight zaps the water and turns it into charged particles
called ions, which Saturn's magnetic field captures and turns into a tube of
energized plasma. The pressure of the solar wind, however, smears the
night-side half of the ring into a sheet of plasma that continuously drifts
into space.
Unlike
Earth's relatively stationary ring current, however, Saturn's rotates with the
planet, Mitchell said.
"Earth
rotates pretty slow compared to the speed of the ring current particles, so the
thing is stationary," he said. But Saturn rotates more than twice as fast
as Earth, dragging Saturn's heavy oxygen ions around the planet in a
counter-clockwise direction.
Although the
Cassini data resolves the mystery of Saturn's ring—which the existence of,
Mitchell said, was only speculative 25 years ago—it has uncovered a new one.
"There's
a point during the rotation where we see an energy spike, so there's something
special about a particular spot on Saturn," he said. "For now,
though, we don't know what it could be."
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