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Sixteen-kilometer-high equatorial ridge
on Iapetus. Original Image credit: NASA/JPL/Cassini-Huygens Mission
Oct 03, 2007
Iapetus Rising
The Cassini space probe recently made another
close flyby of Saturn's strange, warped moon. Do these
images confirm its electrical attributes?
The closest
images of Iapetus ever taken were recently sent to Earth
from the Saturnian system. Cassini flew to within 5000
kilometers of its target, resolving features as small as ten
meters. In our previous
Thunderbolts Picture of the Day articles about this
enigmatic moon, the resemblance to some earthly formations
was noted. Specifically, the physical appearance of
Moqui Marbles found in the deserts of Utah. The striking
similarity can be seen in the
equatorial ridges that are visible on both - stone balls
as big as small eggs and a moon hundreds of kilometers in
diameter.
Some places on
Iapetus are coated with what appears to be frost, covering
many kilometers. The material has not been identified as
actual water ice, but that has been postulated as the most
likely candidate. Scattered over the white background are
dark splotches similar to those discovered on Hyperion
and perhaps arising from the same source: Saturn's moon
Phoebe, the blackest object in the solar system.
In the
close up views of Iapetus, more features have been
identified that mark it as an anomaly in conventional
circles. The
surface is smooth as if it is composed of solidified
bedrock with no breccias and little in the way of dust or
pebbles. However, the
abundant craters of every size are a sign that there has
been some kind of activity violent enough to resurface the
entire moon. The
shape of the craters as they rise up with the terrain is
also distinctive.
In a standard
Newtonian impact scenario, craters should form as conical
holes with a blanket of blast debris surrounding the rims,
sorted from largest to smallest particles depending on
distance from the explosion. On Iapetus, there is a
decidedly different landscape. The craters are clean and
most are found in collections, as if a shotgun blast struck
the area. In locations where the topography has been tilted,
such as near the gigantic mountains called the
Himalayas of Iapetus, the craters are
stretched and pulled as if they have been partially
melted and then immediately reformed. They have flat bottoms
and perpendicular walls, indications that they were cut into
Iapetus by electric discharge machining (EDM) and not
blasted out of it. Another distinctive indicator of EDM on
the surface is the bright crater rims and the smaller
craters surrounding the larger ones.
As Cassini
continues its exploration of Saturn and its many offspring,
more discoveries and more evidence for the electrical
scarring of planets and moons will be presented.
By Stephen Smith
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