Jan
26, 2007
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.
_______________________
Please check out Professor Don Scott's
new book The Electric Sky.
NOTE TO
READERS: Wallace Thornhill, David Talbott, and Anthony
Peratt will share the stage with other investigators of
planetary catastrophe at the British Society for
Interdisciplinary Studies “Conference 2007” August
31-September 2.
GET INFO