picture of the day
"Ponytails" of dust stuck on the wall of
Melas Chasma. Credit: NASA/JPL/Malin Space Science Systems
Nov 07, 2007
Dust Braids in Melas Chasma
The edges of cliffs and canyons on Earth often
display talus slopes caused by erosion. But they start small
and become wide, not the other way around!
Melas Chasma is part of the gigantic
Valles Marineris complex that scars the face of Mars. It
is a tributary canyon with different minerals arranged in
what appear to be sedimentary layers. Because of its unique
geological features, Melas Chasma has been tapped as a
possible landing site for NASA's future Mars Exploration
Rover (MER) projects.
Melas Chasma is thought to result from water and wind
erosion acting on the stone for billions of years. According
to the prevailing theories about Mars, the 4000
kilometer-long trench of Valles Marineris appeared when the
Martian crust was stretched by catastrophic volcanism early
in its history.
the interior of Mars to expand and cool, leaving behind a
series of giant cracks along the equator. Later, during the
"wet phase" in its evolution, water flowed through the
channels, eroding the tributaries and compacting the
sedimentary layers. After eons of time, Mars somehow lost
its water and turned into the lifeless, blasted wasteland
that we see today.
has an atmosphere that is less than 1% of Earth's
atmospheric density at sea level. It is composed almost
entirely of carbon dioxide, although nitrogen and argon make
up about 3%, with trace elements less than 1/10%. The
temperatures on Mars vary with a maximum of 20° C (68° F)
and a minimum of -140° C (-220° F). The atmosphere is so
thin that blowing winds exert almost no pressure on rovers
that are traversing the surface.
Despite a dust
storm several months ago that obscured an entire hemisphere,
the MER B Opportunity reported light pressure increases and
a small amount of sand accumulation. It survived the storm
quite well and continues to return images.
credence to the idea of "blowing" dust on Mars really being
caused by electrostatic discharges from the polar regions. "Electric
dust devils" look like they are carrying dust with them
thousands of meters into the sky and hundreds of kilometers
through the landscape.
previous Thunderbolts Picture of the Day articles about
the Martian surface, we identified anomalous features that
are not easily explained by wind erosion, even if there were
strong winds on Mars. Around Victoria crater's rim and
throughout the ocean of
hematite ripples covering Meridiani Planum are
structures that can be more readily explained if electricity
was involved in their creation. The Martian geography could
have been transformed into the contours that look so
mysterious to conventional scientists by electric current
flowing through the silicon dioxide rock and iron ores that
make up the planet's crust.
is the wall of
Melas Chasma shown at the top of the page. It is part of
larger image that the
Mars Orbital Camera (MOC) took during a flyover in 1999.
The "dust braids" are the strangest of the formations,
appearing to be long tendrils that overlap one another. Some
of the braids have filaments of white stone crossing over
them at right angles. In other cases, the dark iron oxide is
visible underneath the wavering white stone formations. It
looks as if the iron oxide dust was drawn together into long
cords, bunched into a braded shape and then pulled beneath
the silicon dioxide rock.
braids appear to have been "parted" and then twisted like
thick locks of hair. They then fall away into thinner and
thinner strands until they become branching terminations
like lightning bolts. The lightning bolt channels -
Lichtenberg figures - merge into the black ripples of stone
further down and away from the braids. The Lichtenberg
figures are the key to how these braided ropes of iron oxide
were formed: they are the trackways of electric discharges
that gathered the dust and stones into alignment with their
magnetic fields and glassified them permanently into place
on the wall of the chasm.
been calling the ripples that form below the fingers of the
Lichtenberg figures "dunes" and see their formation on Mars
to be much the same as on Earth. Mountains wear down into
sands that are then blown around by winds until they
accumulate into deposits that bear distinctive
characteristics. One of the biggest problems with the "dune"
theory in this case is that the bottom of Melas Chasma is
solid rock - the black ripples are not sand deposits at
There is a "dust
devil" blowing through Melas Chasma in the
large MOC image. The mushroom-shaped, glowing top is
well contrasted with the dark background, so we can say for
certain that it is what NASA scientists have called a "dust
devil" and not a cloud of some kind. Also, its shadow is
visible to the left of the glowing puff. If this is a
rapidly rotating windstorm, hundreds of meters high,
traveling through a field of dunes made up of sand and dust,
then why is it leaving no track as it goes? There is no
trace of its path visible anywhere. The explanation must be
that the "dunes" are not sand and dust and the "dust devil"
is not a whirling wind, but is an ion storm - a rotating
electrical vortex. If electricity is considered a viable
option for explaining the features on Mars rather than wind
and water, then more sense will be made of the "mysteries"
that defy convention.
By Stephen Smith
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