Aug 01,
2006
Martian Butte and Crater
Another feature on Mars that looks strange from the conventional
view begins to look familiar when seen from a plasma point of view.
The caption accompanying this image
(from the Mars Global Surveyor Mars Orbiter Camera) calls the
light-colored flat-top rock with a moat around it a butte. The
caption continues: “The dark landscape that surrounds the butte was
once covered by the same rocks that make up this lonely remnant.”
This is an understandable assumption in view of the butte’s position
on the slope that runs from the 4-kilometer-high southern hemisphere of Mars
to the 2-kilometer-low northern hemisphere. But it overlooks a lot
of features and a lot of possibilities.
The most obvious feature is the moat. If the butte
weren’t there, the depression would probably be called a crater. But
it’s difficult to imagine an impact that would generate a central
rebound in the shape of a layered butte. (It’s also difficult to
imagine an erosion process that would strip away the light-colored
layers for miles around and carve a uniformly wide moat—with a
crater-like rim—around the steep cliffs of the butte. This may be why the moat is not
mentioned.)
Another feature, more easily overlooked, is the system
of ridges and cleanly cut grooves radiating away from the butte.
Perhaps planetary scientists assumed these to be familiar erosion
patterns. But this is not an
unusual erosion pattern, except that many of the ridges and grooves
appear to run continuously from the butte into the moat over the rim
and onto the plain.
Also, the “dark landscape” is not a local feature:
It’s part of an extensive dark region just to the east of Valles Marineris.
The awareness of
plasma discharge
as an erosion process enables one to imagine
other possibilities. A “butte crater” is similar in many respects to
rampart and
pedestal craters.
It’s reminiscent of
domed craters—which
have been reproduced in a plasma lab. It’s merely a variation on
layered craters.
The rotating
filaments in a discharge channel that carves a crater can be small enough to leave a
large central area undisturbed. The secondary coronal discharge
channels pulling charge (and surface material with it) into the
strongest region of the electric field—around the edge of the
primary channel at the rim—will tend to be arranged symmetrically
inside and out. And if the arc that cut this crater was only a small
component of the much larger thunderbolt that carved
Valles
Marineris and
its extensions, it would have been situated in the more diffuse area
that not only removed much of the surface electrically but
scorched it
as well.
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