Saturn's moon blows bubbles.
KMel_TorTelli_KTarra
By SPACE.com Staff
posted: 14 April 2010
07:02 pm ET
As Saturn's icy moon Enceladus circles around the ringed giant, it
plows through the charged plasma surrounding the planet, leaving a
complex pattern of ripples and bubbles in its wake.
Enceladus sits deep within Saturn's protective magnetic casing, called
a magnetosphere, which is filled with electrically charged particles
(plasma) that originate from both the planet its many moons.
NASA's Cassini spacecraft has conducted nine flybys of the mysterious
sixth-largest moon since 2005.
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The closest of these flybys brought the probe to within just 15.5
miles (25 kilometers) of Enceladus's surface, which many scientists
believe conceals a saline ocean. Heated vents at the south pole of the
moon release a plume of material, consisting mainly of icy grains and
water vapor, into space.
Cassini measurements show that both the moon and its plume are
continuously soaking up the plasma, which rushes past at around 67,000
mph (108,000 kilometers per hour), leaving a cavity downstream. In
addition, the most energetic particles which zoom up and down Saturn's
magnetic field lines are swept up, leaving a much larger void in the
high energy plasma. Material from Enceladus, both dust and gas, is
also being charged and forming new plasma.
Cassini scientists have also discovered mysterious spiky features in
the plasma wake of Enceladus that present a complex picture of
readjustment downstream from the icy moon.
"Eventually the plasma closes the gap downstream from Enceladus but
our observations show that this isn't happening in a smooth, orderly
fashion," said Sheila Kanani of University College London, who helped
discover the odd features. "We are seeing spiky features in the plasma
that last between a few tens of seconds and a minute or two. We think
that these might represent bubbles of low energy particles formed as
the plasma fills the gap from different directions."
Since Cassini arrived at Saturn, it has been building up a picture of
the vital and unexpected role that Enceladus plays in Saturn's
magnetosphere. Enceladus may play a role similar to Jupiter's moon Io,
which pumps plasma into Jupiter's environment. A picture of plasma
adjustments in the wake of Enceladus could provide clues to how plasma
gets transported around the Saturnian environment.
"Enceladus is the source of most of the plasma in Saturn's
magnetosphere, with ionized water and oxygen originating from the
vents forming a big torus of plasma that surrounds Saturn. We may see
these spiky features in the wake of Saturn's other moons as they
interact with the plasma but, to date, we have only studied Enceladus
in sufficient detail," Kanani said.