"They're everywhere," DeLory said via cell phone from
Arizona. "You can look out at the horizon and see ten
of them at a time."
Though 10 to 100 times smaller than dust storms on
Mars, Arizona dust devils nevertheless will give the
researchers an idea of the effect dust storms could
have on sensitive instruments aboard future Mars landers,
and how they might affect robots exploring the surface.
The tests also will help identify what instruments are
needed to study dust devils on Mars.
"We're studying terrestrial versions so that when we
fly robotic instruments to Mars, which has tremendous
dust devils all over the planet, we will be able to
understand the observations," said DeLory, an assistant
research physicist with UC Berkeley's Space Sciences
Laboratory. He is one of the principle investigators
with Project Matador, led by Nilton Renno and Peter
Smith of the University of Arizona.
One of the main concerns is electrical discharges within
dust devils, which could fry computers and electronic
circuits and disable radio communications equipment
aboard a lander or robot.
"Dust caught up in these vorticies undergoes frictional
charging, like rubbing your hair with a balloon, generating
voltages of many thousands of volts," DeLory said. Using
special antennas and sensors, he and his collaborators
are studying the DC (direct current) voltages generated
within the twisters, as well as wind speeds and particle
Such data "would allow us to replay a large (dust devil)
event with accurate, sub-second resolution of position,
velocity, size, wind speed, dust concentration and radio
noise," Renno said. "We should be able to completely
characterize a dust devil as it moves over our sensors."
They also are looking at how dust gets airborne, and
whether electrical charges make this easier or more
"If the electrical field is big enough, it could repel
the dust and make it harder to get into the air," DeLory
The team began this year's tests on May 20 and plan
to stay in Eloy for three and a half weeks to get sufficient
data on dust devils. In their first tests last year,
they chased dust devils around with a truck crammed
with instruments and sensors. This year, they are placing
the instruments in one spot and waiting for the ever-present
dust devils to blow over.
"Last year was a lot of fun stalking dust devils, and
we got great recordings," DeLory said. "But a metal
truck can interfere with making sensitive electrical
The researchers also hope to learn about the effects
dust devils have on our own atmosphere.
"The idea that dust devils and convective plumes play
an important role in the vertical transport of heat
and aerosols is novel and needs testing," Renno added.
"It's also risky. No one has experience in measuring
what convective plumes and dust devils contribute to
heat and aerosols transport. This pilot study will be
a learning experience for us."
Convective air and dust devils are a known hazard for
aviation - up to 10 percent of accidents with light
aircraft, sailplanes, helicopters and blimps are caused
by gusts associated with these convective winds. Earth's
dust devils may play an important role in climate change,
atmospheric photochemistry and ocean biochemistry.
Smith, head of the Imager for Mars Pathfinder (IMP)
camera on the hugely successful Pathfinder mission that
landed on Mars in 1997, and Renno, an atmospheric scientist
who is an expert on atmospheric convection, began collaborating
in dust devil research in 1996. Their analysis of Mars
Pathfinder meteorological data showed that dust devils
blast over the Mars Pathfinder landing site with windspeeds
greater than 140 mph and are an important source of
dust in the martian atmosphere.
The 2002 field test expands on a Matador experiment
that Smith and Renno organized last June at the same
location. One surprising result from that four-day experiment
was that even small terrestrial dust devils produce
radio noise and electrical fields greater than 10,000
volts per meter. If they were on Mars, they would generate
long-lived, charged particles powerful enough to trigger
electrical discharges in the martian atmosphere.
Matador, funded by NASA's Human Exploration and Development
of Space program and by the National Science Foundation,
also involves collaborators from the Wageningen University
in the Netherlands, and IMADES, or Instituto del Medio
Ambiente y el Desarrollo Sustentable del Estade de Sonora,
in Hermosillo, Sonora, Mexico.
Matador team scientists involved in the 2001 and 2002
experiments also include John Marshall of NASA Ames
Research Center; William Farrell of NASA Goddard Space
Flight Center; Allan Carswell of Optech, Ontario, Canada;
and Barry Hillard of the NASA John Glenn Research Center.