Satanic winds: looking at dust devils on Earth and Mars.How to study a dust devil dust devil: see whirlwind. : Sit in your truck on a dry lake bed and wait for a minitornado to spring up within sight. Eyeball See eyeballs and eyeball driven. its path and guess where it's headed. Drive to a spot in that direction, shut off the engine, and hope that the vortex sweeps over you and your truckful of instruments.
"It's really passive-aggressive," says Gregory T. Delory, a planetary scientist at the University of California, Berkeley The University of California, Berkeley is a public research university located in Berkeley, California, United States. Commonly referred to as UC Berkeley, Berkeley and Cal . Unlike the pursuit of monster Midwestern tornadoes, which can have two-by-fours and cows flying around in 500-kilometer-per-hour winds, dust devil studies don't have much excitement in the chase. The desert whirlwinds are typically only a few hundred meters tall and feature 60-km/hr gusts.
But within dust devils For other uses of this phrase, see Dust devil (disambiguation).
Dust Devils is an independently published role-playing game set in a spaghetti western setting, written by Matt Snyder. , electric fields can be surprisingly strong. New research suggests that those electric fields help the whirlwind lift material off the ground, enabling dust devils to pump enough dust into Earth's atmosphere to possibly affect climate (SN: 9/29/01, p. 200).
Results of these earthbound earth·bound also earth-bound
1. Fastened in or to the soil: earthbound roots.
a. investigations have implications for explorations of other planets. On Mars, a desert planet where dust devils are common and unusually large, the whirlwinds result from severe atmospheric turbulence. Recent studies suggest that the electric fields in dust devils on the Red Planet are strong enough to cause chemical changes in the atmosphere there, including the creation of hydrogen peroxide hydrogen peroxide, chemical compound, H2O2, a colorless, syrupy liquid that is a strong oxidizing agent and, in water solution, a weak acid. It is miscible with cold water and is soluble in alcohol and ether. . That reactive substance may sterilize sterilize /ster·i·lize/ (ster´i-liz)
1. to render sterile; to free from microorganisms.
2. to render incapable of reproduction.
1. Mars' surface, and its presence could explain some of the odd soil chemistry observed by the Mars Viking landers in the 1970s.
KICKING UP DUST Although quite different in size and strength, tornadoes and dust devils both result from atmospheric convection. When water vapor condenses inside a thunderstorm thunderstorm, violent, local atmospheric disturbance accompanied by lightning, thunder, and heavy rain, often by strong gusts of wind, and sometimes by hail. , the heat that's released drives fast-rising air masses that can spawn tornadoes. On a smaller scale, the more languid ascent of air warmed at Earth's surface--the thermals that buzzards and glider pilots use to gain altitude--produces the convection that triggers dust devils.
Packets of ground-heated air typically rise between 3 and 6 km before they cool, spread, and fall back toward the ground, says Nilton O. Renno, an atmospheric scientist at the University of Michigan (body, education) University of Michigan - A large cosmopolitan university in the Midwest USA. Over 50000 students are enrolled at the University of Michigan's three campuses. The students come from 50 states and over 100 foreign countries. in Ann Arbor. Within the large mass of circulating air, called a convection cell, vortices vor·ti·ces
A plural of vortex. often form in the region between the upwelling up·well·ing
1. The act or an instance of rising up from or as if from a lower source: an upwelling of emotion.
2. center and the downdrafts along its outer rim, he notes.
When those swirling air masses touch the ground and pick up loose material, they become visible as dust devils.
In recent years, scientists have measured strong electrical fields inside dust devils. The airborne particles become electrically charged as they bump and scrape each other, says Renno. The lighter particles in the whirlwind tend to develop a negative charge, and the heavier ones, a positive charge. Because the light particles typically rise higher and faster than heavier ones, the separation of charges creates an electrical field that can measure more than 80 kilovolts per meter (kV/m). The whirling charged particles also create small magnetic fields magnetic fields,
n.pl the spaces in which magnetic forces are detectable; created by magnetostrictive ultrasonic scalers to cause the tips of instruments such as ultrasonic scalers to vibrate. that fluctuate between 3 and 30 times each second (SN: 2/8/03, p. 94).
Lab experiments indicate that the strong electrical fields inside dust devils help the vortices boost material off the ground, Renno and his colleague Jasper F. Kok report in the Aug. 28 Geophysical Research Letters Geophysical Research Letters is a publication of the American Geophysical Union. GRL is the organization's only letters journal. Since its introduction in 1974, GRL has published only short research letters, typically 3-5 pages long, which focus on a specific discipline or . An electrical field would need to measure at least 150 kV/m to overcome gravity and lift a grain of sand in the absence of wind, the tests suggest. However, a field half that value would enable wind to pick up many particles, says Kok.
With the aid of their internal electric fields, dust devils pump a lot of dust into the atmosphere. Field tests suggest that a dust devil lifts about 1 gram of dust per second from each square meter of ground over which it passes, says Jacquelin Koch, an atmospheric scientist at the University of Michigan in Ann Arbor. Therefore, a large dust devil--about 100 m across at its base--can lift about 15 metric tons of dust during its 30-minute life span.
Dust devils may seem innocuous compared with the immense dust storms that carry material across oceans (SN: 9/29/01, p. 200). However, the small whirlwinds, in aggregate, pump more material into the atmosphere than large storms do, says Koch. Massive dust storms sweep the world's deserts only a few times each month and contribute about 8 percent of the mineral dust that reaches the atmosphere each year. The hundreds of dust devils spawned daily in deserts throughout the summer together loft about three times that much, Koch and Renno reported last December at the American Geophysical Union The American Geophysical Union (or AGU) is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 140 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and meeting in San Francisco.
SPACE DUST On Earth, individual dust devils are usually no more than a nuisance. On Mars, however, such whirlwinds are larger and more common than their terrestrial kin. Martian dust devils may pose a threat to both robotic and human exploration.
As on Earth, dust devils on Mars arise from atmospheric turbulence. The temperature difference between the planet's surface and the atmosphere just above it can be much higher on Mars than on Earth, making the dust devils larger and stronger, says William M. Farrell, a geophysicist at NASA's Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles northeast of Washington, D.C. in Greenbelt, Md. He's a member of a NASA NASA: see National Aeronautics and Space Administration.
in full National Aeronautics and Space Administration
Independent U.S. scientific panel assembled in 2004 to analyze risks to human missions to the Red Planet.
Dust devils within 10 km of a spaceship port on Mars could be a hazard for take-offs and landings, Farrell speculates. Before creating such a Red Planet base, space agencies should send landers, rovers, and other instruments to monitor dust devils and larger dust storms to determine whether those phenomena pose a threat, he and his colleagues suggested in a June 2005 report.
Many studies indicate that dust devils scour scour, scours
1. the chemical and physical cleaning of fleece wool.
see dietary diarrhea.
see secondary nutritional copper deficiency. much of the Red Planet's surface, which covers as much area as Earth's continents do. Cameras on Mars landers have seen hundreds of the dusty whirlwinds, says chief rover scientist Steven W. Squyres of Cornell University.
The shadows of monstrous whirlwinds thick with dust have even been seen from craft orbiting Mars. The dimensions of those shadows indicate that some Martian dust devils grow to be several hundred meters across and up to 9 km tall, about 10 times the size of their cousins on Earth, says Paul E. Geissler, a planetary geologist with the U.S. Geological Survey in Flagstaff Flagstaff, city (1990 pop. 45,857), seat of Coconino co., N Ariz., near the San Francisco Peaks; inc. 1894. Lumbering, ranching, and a lively tourist trade thrive in the region, where many ruined pueblos, numerous state parks, several lakes, and large pine forests , Ariz.
The largest of the massive Martian whirlwinds, 5 km across at high altitude, can rival earthly tornadoes and "look like mountains" in the orbital images, he notes.
Evidence of past Martian dust devils can be detected from orbit too. A whirlwind leaves linear or looping trails as it sweeps away light-colored dust to reveal darker material, says Timothy I. Michaels, an atmospheric scientist at Southwest Research Institute Southwest Research Institute (SwRI), headquartered in San Antonio, Texas, is one of the oldest and largest independent, nonprofit, applied research and development (R&D) organizations in the United States. Founded in 1947 by Thomas Slick, Jr. in Boulder, Colo. Some orbital images have caught dust devils in the act of making such tracks. Similar tracks appear in satellite images of Earth's southern Sahara but aren't obvious to observers on the ground (SN: 5/8/04, p. 302).
Rover-based analyses of dust devil tracks on Mars indicate that most such trails are no more than a few micrometers deep, he notes. Because dust devils ate pushed along by other weather systems, researchers can use the tracks to deduce the strength and consistency of the prevailing winds in areas of Mars.
No area of Mars may be safe from the whirlwinds. Satellites have recorded dust devil tracks in all regions of Mars and at all elevations--even inside the crater atop the 24-km-tall Olympus Mons, the largest volcano known in the solar system. However, some Martian regions seem to be more afflicted af·flict
tr.v. af·flict·ed, af·flict·ing, af·flicts
To inflict grievous physical or mental suffering on.
[Middle English afflighten, from afflight, by the whirlwinds than others are, says Patrick L. Whelley, a geologist at Arizona State University Arizona State University, at Tempe; coeducational; opened 1886 as a normal school, became 1925 Tempe State Teachers College, renamed 1945 Arizona State College at Tempe. Its present name was adopted in 1958. in Tempe.
In the Red Planet's southern hemisphere, orbital images show an average of about 0.6 dust devil track per square kilometer, but pictures of the northern hemisphere show only one-tenth as many, Whelley and his colleague Ronald Greeley reported at the San Francisco meeting.
That disparity probably stems from the eccentricity of Mars' orbit, says Whelley. Summer comes to the northern hemisphere when Mars is at its farthest from the sun, about 249 million miles away. However, dust devil season comes to the southern hemisphere at the opposite side of Mars' orbit, when the planet is only 207 million miles from the sun. Because the southern hemisphere thus receives 40 percent more solar energy per square meter in summertime than the northern hemisphere does, dust devils are more frequent in the southern hemisphere.
Nevertheless, dust devil tracks appear even in the high latitudes of Mars' northern hemisphere, above that planet's equivalent of Earth's Arctic Circle. Scientists are now planning a Mars mission that will put a lander down at high latitudes, so they're closely scrutinizing orbital images to get an idea of the region's geology and weather, says R. David Baker, an atmospheric scientist at Austin College in Sherman, Texas.
None of the 1,558-or-so clear images of sites in that latitude band shows a dust devil in action. However, about 10 percent of those pictures include dust devil tracks, says Baker. The trails range in length from 500 m to more than 16 km. He and his colleagues also reported their findings in December at the San Francisco meeting.
"We were surprised at the number of dust devil [tracks] we saw at high latitude," says Baker. "There was much more [past] activity than we expected."
The lander that will set down in this polar region will carry an atmospheric-pressure sensor as well as an upward-looking laser-radar device, so it will be equipped to study any dust devils that happen past the craft, says Baker.
STRANGE CHEMISTRY The denser an atmosphere, the more effectively its molecules block the flow of charged particles. On Earth, where the atmosphere is dense, electric fields inside dust devils aren't strong enough to accelerate dust particles to speeds where they strip electrons off molecules.
On Mars, however, the atmosphere is less than 1 percent as dense as Earth's, so speeding charged particles begin to break down atmospheric gases when electric fields build up to 25 kV/m. That's well below the value of the electric fields that build up in terrestrial dust devils, says Gregory T. Delory, a planetary scientist at the University of California, Berkeley. If Martian dust devils generate such fields, they may spark significant changes in atmospheric chemistry, he notes.
Electrons stripped from the gas molecules in Martian air would be accelerated by the electric fields. Lab tests suggest that those charged particles would attach themselves to carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. molecules to make negative ions and would split carbon dioxide into carbon monoxide carbon monoxide, chemical compound, CO, a colorless, odorless, tasteless, extremely poisonous gas that is less dense than air under ordinary conditions. It is very slightly soluble in water and burns in air with a characteristic blue flame, producing carbon dioxide; and oxygen ions. The speeding electrons would also split water vapor into hydroxyl hydroxyl /hy·drox·yl/ (hi-drok´sil) the univalent radical OH.
The univalent radical or group OH, a characteristic component of bases, certain acids, phenols, alcohols, carboxylic and hydrogen ions, says Delory.
Reactions of hydrogen ions, oxygen atoms, and hydroxyl ions produce hydrogen peroxide, [H.sub.2][O.sub.2], the highly reactive chemical that's used on Earth to bleach hair and disinfect To remove the virus code that has attached itself to a legitimate file. Sometimes, the antivirus program cannot untangle the code, and the infected file has to be deleted. See quarantine. scrapes.
The typical lifetime of a hydrogen peroxide molecule in Martian atmosphere is about 2 days, says Delory. However, in the presence of large electric fields, hydrogen peroxide wouldn't remain in the atmosphere as a gas. So, the hydrogen peroxide that's formed inside a dust devil would either crystallize crys·tal·lize also crys·tal·ize
v. crys·tal·lized also crys·tal·ized, crys·tal·liz·ing also crys·tal·iz·ing, crys·tal·liz·es also crys·tal·iz·es
1. in the air and fall as snow or crystallize on the surface of the whirling dust particles.
Either way, the peroxide would quickly fall to the ground, where, if protected from sunlight by a shallow layer of dust, it could survive for more than 4 years. Delory, Renno, and their colleagues reported their analyses in the June Astrobiology astrobiology: see exobiology. .
The presence of dust devil-produced peroxide could explain some of the odd results from a battery of soil chemistry experiments performed onboard the Mars Viking lander in the 1970s. Those tests detected highly reactive chemicals but didn't find any sign of organic material, says Delory. Even if there hadn't been life on Mars Scientists have long speculated about the possibility of life on Mars owing to the planet's proximity and similarity to Earth. It remains an open question whether life exists on Mars now, or existed there in the past. , scientists expected to find traces of organic chemicals brought to the planet by meteorites Meteorites
See also astronomy.
the science of aerolites, whether meteoric stones or meteorites. Also called aerolitics.
the study of meteorites. Also called meteoritics. .
Highly reactive peroxide would scour organic chemicals from Martian soil, says Delory. That process would make the surface of the Red Planet hostile to life. Furthermore, because the planet lacks an ozone layer, large quantities of ultraviolet radiation reach Mars' surface. Deep in the soil, where neither ultraviolet radiation nor peroxide infiltrates, however, life might survive.
"The jury's still out as to whether there is life on Mars," Delory notes.
Indeed, the jury's still out on many things about the Red Planet. For instance, "there's still a lot we don't understand about the chemistry of the atmosphere and soils of the planet," he adds. The researchers' theory about dust devils generating peroxide, Delory notes, could be verified by future Mars rovers or landers if they're equipped with an electric field sensor and can analyze Mars' atmospheric chemistry.