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Electric Dust Devils On Mars
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tomas w
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Mar 21, 2005 13:31 PST
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Dear Friends,
http://www.thunderbolts.info/tpod/2005/arch05/00current.htm
THUNDERBOLTS PICTURE OF THE DAY
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Credit: University of Michigan
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Mar 21, 2005
Electric Dust Devils on Mars
Giant columns of whirling dust on Mars add new surprises in planetary
exploration. Experts now agree that analogous “dust devils” on Earth
contain powerful electric fields.
In the larger scheme of things, dust devils on Earth have always been
treated as trivial phenomena. But this perception has changed with
recent discoveries by investigators in Arizona and Nevada. They found
that dust devils have a strong electric field, often exceeding 4,000
volts per meter.
The discovery came as a surprise. Prior thermal and mechanical models of
dust devils had predicted no electric fields. But ironically, it was
discoveries on the planet Mars that provoked a reconsideration of
atmospheric vortices on earth. On Mars, “dust devils” much larger than
terrestrial tornadoes sporadically rake across the surface, achieving
things that traditional meteorology considered impossible in the nearly
airless Martian environment. The tracks of these Everest-sized
“whirlwinds” speak for high-energy activity never imagined, inscribing
the Martian surface with their darkened tracks. (See Picture of the
Day: Europa and Mars
Atmospheric density on Mars is only one percent that of Earth. How could
a Martian “wind” excavate soil with sufficient energy to leave extensive
tracks clearly visible from space? Of course, the same question is posed
by the planet’s global dust storms, these having been observed for
several decades.
In July, 1999, Wallace Thornhill wrote “The 5 mile high dust devils on
Mars and the global Martian dust storms are, I believe, a manifestation
of electric discharges on Mars.” And more recently, he wrote “Make no
mistake, the Martian dust devils are tornadoes that dwarf their earthly
counterpart… Clouds are not required to generate them. They are an
atmospheric electric discharge phenomenon”.
Today, interest in the electrical nature of Martian dust devils is
growing rapidly. In a report in Astrobiology Magazine, Dr. William
Farrell of NASA's Goddard Space Flight Center reports: “If martian dust
devils are highly electrified, as our research suggests, they might give
rise to increased discharging or arcing in the low-pressure Martian
atmosphere”. According to Thornhill, such arcing in the rarified
atmosphere of Mars would have the appearance of a glow discharge, not
unlike that of a lightning “sprite” above terrestrial thunderstorms.
Our picture above is a University of Michigan artist’s impression of an
electrified Martian “dust devil”. Did the artist intuitively include a
glow discharge near its base? In the Global Surveyor pictures of these
Martian dust columns, the eerie glow is a dramatic contrast to the
darkened dust they lift into the atmosphere. (We’ve placed a picture
here).
To see the electrical nature of these towering vortices is to answer the
question we posed in our last Picture of the Day. Why does the Martian
surface present both dark and light streaks, just as we see on Jupiter’s
moon Europa? Experiments with laboratory arcs have shown that the
discharges will “burn” soil, leaving a darkened look Though enigmatic to
planetary scientists, such darkening is evident across vast regions of
Mars. It is especially concentrated in regions of heavy dust devil
tracks, typically appearing amid dense populations of small dark spots.
In those regions where electric activity has burnt the soil directly, or
where darkened material was raised into the atmosphere and then drifted
back to the surface, the layer of such material is apparently quite
thin. It is thus easy to imagine that when lower energy dust devils have
subsequently moved across such surfaces, they removed the layer of dark
material and exposed the original lighter soil below.
Unfortunately, even with the new interest in electrified whirlwinds on
Mars, most discussion still draws on old thermal and mechanical concepts
of atmospheric “whirlwinds”, without regard to the role of larger
electric fields in their generation. Most of the “new” theoretical
models of electrified dust devils, for example, have not broken out of
the earlier paradigm. To get the electric field, the theorists believe
they have to first “separate charge”; and that requires energetic
movement and collisions of both large and small soil particles. In their
collisions, the larger particles become positively charged and the
smaller become negatively charged. Then the power of the wind separates
the particles into regions of different particle size, creating an
electric field.
But in the near vacuum of Mars’ atmosphere, how were the larger grains
of soil raised miles into the sky in the first place, with a force
sufficient to generate the apparent high voltages? In the electric
model, no local dynamo is required for charge separation. Charge
separation already exists in the atmosphere. Without Earth’s storm
clouds to lower charge to ground in the form of lightning, the
discharges on Mars take a towering tornadic form. The larger
interplanetary electrical circuitry is the true driver of the whirlwind,
just as it drives the global dust storms on Mars, and just as it drives
weather systems on Earth. If this is true, then the power of Martian
“dust devils” can teach us much about the behavior of electricity in the
solar system.
See tomorrow’s Picture of the Day, “Dust Devils—or Tornadoes?”
See also: Electric Dust Devils
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