Asteroid Dust May Influence Weather, Study Finds

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Sandia National Laboratories
August 25, 2005

Asteroid dust may influence weather, study finds

Nature paper: Burning asteroids may play 'more important climate
role than previously recognized'

ALBUQUERQUE, N.M. - Dust from asteroids entering the atmosphere may
influence Earth's weather more than previously believed, researchers
have found.

In a study to be published this week in the journal Nature, scientists
from the Australian Antarctic Division, the University of Western
Ontario, the Aerospace Corporation, and Sandia and Los Alamos national
laboratories found evidence that dust from an asteroid burning up as it
descended through Earth's atmosphere formed a cloud of micron-sized
particles significant enough to influence local weather in Antarctica.

Micron-sized particles are big enough to reflect sunlight, cause local
cooling, and play a major role in cloud formation, the Nature brief
observes. Longer research papers being prepared from the same data for
other journals are expected to discuss possible negative effects on the
planet's ozone layer.

"Our observations suggest that [meteors exploding] in Earth's atmosphere
could play a more important role in climate than previously recognized,"
the researchers write.

Scientists had formerly paid little attention to asteroid dust, assuming
that the burnt matter disintegrated into nanometer-sized particles that
did not affect Earth's environment. Some researchers (and science
fiction writers) were more interested in the damage that could be caused
by the intact portion of a large asteroid striking Earth.

But the size of an asteroid entering Earth's atmosphere is significantly
reduced by the fireball caused by the friction of its passage. The mass
turned to dust may be as much as 90 to 99 percent of the original
asteroid. Where does this dust go?

The uniquely well-observed descent of a particular asteroid and its
resultant dust cloud gave an unexpected answer.

On Sept. 3, 2004, the space-based infrared sensors of the U.S.
Department of Defense detected an asteroid a little less than 10 meters
across, at an altitude of 75 kilometers, descending off the coast of
Antarctica. U.S. Department of Energy visible-light sensors built by
Sandia National Laboratories, a National Nuclear Security Administration
lab, also detected the intruder when it became a fireball at
approximately 56 kilometers above Earth. Five infrasound stations, built
to detect nuclear explosions anywhere in the world, registered acoustic
waves from the speeding asteroid that were analyzed by LANL researcher
Doug ReVelle. NASA's multispectral polar orbiting sensor then picked up
the debris cloud formed by the disintegrating space rock.

Some 7.5 hours after the initial observation, a cloud of anomalous
material was detected in the upper stratosphere over Davis Station in
Antarctica by ground-based lidar.

"We noticed something unusual in the data," says Andrew Klekociuk, a
research scientist at the Australian Antarctic division. "We'd never
seen anything like this before - [a cloud that] sits vertically and
things blow through it. It had a wispy nature, with thin layers
separated by a few kilometers. Clouds are more consistent and last
longer. This one blew through in about an hour."

The cloud was too high for ordinary water-bearing clouds (32 kilometers
instead of 20 km) and too warm to consist of known manmade pollutants
(55 degrees warmer than the highest expected frost point of
human-released solid cloud constituents). It could have been dust from a
solid rocket launch, but the asteroid's descent and the progress of its
resultant cloud had been too well observed and charted; the pedigree, so
to speak, of the cloud was clear.

Computer simulations agreed with sensor data that the particles' mass,
shape, and behavior identified them as meteorite constituents roughly 10
to 20 microns in size.

Says Dee Pack of Aerospace Corporation, "This asteroid deposited 1,000
metric tons in the stratosphere in a few seconds, a sizable
perturbation." Every year, he says, 50 to 60 meter-sized asteroids hit
Earth.

Peter Brown at the University of Western Ontario, who was initially
contacted by Klekociuk, helped analyze data and did theoretical
modeling. He points out that climate modelers might have to extrapolate
from this one event to its larger implications. "[Asteroid dust could be
modeled as] the equivalent of volcanic eruptions of dust, with
atmospheric deposition from above rather than below." The new
information on micron-sized particles "have much greater implications
for [extraterrestrial visitors] like Tunguska," a reference to an
asteroid or comet that exploded 8 km above the Stony Tunguska river in
Siberia in 1908. About 2150 square kilometers were devastated, but
little formal analysis was done on the atmospheric effect of the dust
that must have been deposited in the atmosphere.

The Sandia sensors' primary function is to observe nuclear explosions
anywhere on Earth. Their evolution to include meteor fireball
observations came when Sandia researcher thingy Spalding recognized that
ground-based processing of data might be modified to record the
relatively slower flashes due to asteroids and meteoroids. Sandia
computer programmer Joe Chavez wrote the program that filtered out
signal noise caused by variations in sunlight, satellite rotation, and
changes in cloud cover to realize the additional capability. The Sandia
data constituted a basis for the energy and mass estimate of the
asteroid, says Spalding.

The capabilities of defense-related sensors to distinguish between the
explosion of a nuclear bomb and the entry into the atmosphere of an
asteroid that releases similar amounts of energy - in this case, about
13 kilotons - could provide an additional margin of world safety.
Without that information, a country that experienced a high-energy
asteroid burst that penetrated the atmosphere might provoke a military
response by leaders who are under the false impression that a nuclear
attack is underway, or lead other countries to assume a nuclear test has
occurred.

More detailed papers are slated for the Journal of Geophysical Research
and the Journal of Meteoritics and Planetary Science, Pack says.

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Sandia is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin company, for the U.S. Department of Energy's National
Nuclear Security Administration. Sandia has major R&D responsibilities
in national security, energy and environmental technologies, and
economic competitiveness.