rusty_red_mars_000914 Scientists have recreated
Martian conditions in test tubes, producing a "disinfectant" that may help explain the planet's rusty red color and why life and organic material have not been found on the surface.
| What MAOS will measure |
| How strong an oxidant is the atmosphere on Mars? A proposed science instrument called MAOS aims to learn just that, by measuring how quicklythings rust on the planets surface. The instrument may be the only NASA contribution to the British Beagle 2 mission in 2003. Want to learn more? Click here . |
The chemical is superoxide; a "free radical" or oxidant like those implicated in human cell damage from cigarette smoking, radiation and diseases like heart disease and cancer.
"You would not expect life to exist at the immediate surface of
Mars because production of these oxygen radicals will destroy organic molecules," said planetary geochemist Albert Yen of NASAs Jet Propulsion Laboratory (JPL) in Pasadena, California. "If life exists on Mars, it needs to be in a place where these chemicals dont exist."
Composite panorama by Mars Pathfinder cameras showing the Sojourner Rover and red Martian terrain. An oxidant chemical may help explain Mars' red color and why organic chemicals have not been found on the planet.
That means microbial life would have to hide more than four inches (10 centimeters) underground, in cracks in rocks, in groundwater or near the polar caps, he said.
Ever since 1976, when the Viking landers found Martian soil gave off oxygen when exposed to water vapor, scientists have known something in Martian soil acts as an oxidant, but they did not know what. The new study suggests Martian soil contains superoxide anions, which are negatively charged oxygen molecules.
With little water vapor in Mars atmosphere, the superoxide is not consumed in reactions with water. Instead, it apparently persists in Martian soil, reacting with and decomposing any organic material that forms on Mars or is deposited there by
meteorites, Yen and colleagues concluded.The new study appears in the September 15 issue of the journal Science. Yens co-authors were JPL chemist Sam Kim, JPL materials scientist Mike Hecht, chemist Martin Frant of Chemotics Consulting in Newton, Massachusetts, and planetary scientist Bruce Murray of the California Institute of Technology in Pasadena.
Oxidation equals breakdown
Oxidation makes metal rust and foods turn rancid and brown. The body normally produces oxidants, also known as free radicals, as food is metabolized. Unstable oxidant molecules have been implicated in cell damage such as from cigarette smoke and radiation and in cancer, heart disease, loss of central eyesight and perhaps hastened aging.
The researchers started their experiment with 0.0035-ounce (100-milligram) samples of labradorite, a feldspar mineral found in Martian soil.
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The samples were placed in test tubes, which were filled with the same gases found in Mars atmosphere. The tubes were chilled to 22 degrees below zero Fahrenheit (minus 30 Celsius), then bombarded for minutes, to one week, with ultraviolet radiation like that emitted by the
sun."Its hard to get Mars into a laboratory, but we do our best to simulate those conditions," Yen said. "We have small test tubes with a little bit of Mars inside."
The radiated mineral samples then were examined with a device that works on the same principle as a medical magnetic resonance imaging (MRI) machine that looks at internal body structures. The examination showed that superoxide ions formed on the surface of the mineral grains.
Yen said the superoxide could be thought of as a natural disinfectant on Mars, breaking down organic material to prevent microbial life.
Other researchers previously suggested the oxidant in Martian soil could be hydrogen peroxide, potassium superoxide, barium superoxide or other chemicals. Yen believes simple superoxide is at work on Mars because formation of other oxidants is "unlikely under Martian conditions."
Most of Mars' red hue "is likely old - from a wet period when the rusty looking soil could have been produced rapidly."
The reddish hue of Martian soil has been attributed to water oxidizing or rusting iron minerals a few billion years ago when Mars was warm and wet, Yen said.
Now that
Mars is cold and dry, modern-day soil rusting may be caused by superoxide that forms on minerals exposed to ultraviolet rays in sunlight, he added.Ancient red hue
Superoxide could oxidize iron in Martian soil to turn it red, but the process is slow, said Aaron Zent, a planetary scientist at NASAs Ames Research Center in Mountain View, California. So most of Mars red hue "is likely old from a wet period when the rusty looking soil could have been produced rapidly," he said.
The idea that superoxide destroys any organic materials on Martian soil "is well-informed conjecture," said Zent, who called the new study "very good work" that probably was "partially right."
Ultraviolet radiation likely does form superoxide on Martian soil, but Zent also believes other oxidants form on Mars from other processes, such as the interaction of UV light and small amounts of water vapor in the atmosphere.
When the twin
Vikings landed on Mars in 1976, some researchers initially thought they found signs of life when nutrients added to the soil seemed to be consumed. But scientists concluded it was a chemical reaction oxidation in Mars' soil that was releasing oxygen and decomposing added nutrients and any native organic materials.Several previous studies on Earth exposed Mars-like minerals to ultraviolet light, and found the minerals behaved as they did on Mars. But none of those experiments identified the specific oxidant, said Harold "Chuck" Klein, NASAs Viking biology team leader during the 1970s.
Experiments in the 1970s suggested organic chemicals should form naturally on Mars, which also should get organics from meteorites, Klein said from Palo Alto, California.
Yet the Vikings found no organic chemicals on Mars, so it "makes sense" that organics are being destroyed by an oxidizing chemical like superoxide, he added.
The
Viking landers found the oxidizing substance on Mars was as deep as 4 inches (10 centimeters) beneath the surface and also under rocks, Klein said. Yen believes superoxide could migrate slowly away from sunlit surfaces where it formed.The idea that superoxide might be the oxidant in Martian soil arose from a problem during development of the
Hubble Space Telescopes cameras.A puff of moist air
When ultraviolet light struck a
Hubble camera sensor, it changed the photographic exposure in unpredictable ways. Hecht was on a team to figure out why. Camera engineers told the team a camera sensor could be reset to normal by huffing on it with a breath of moist air.The team concluded UV light made superoxide form on the camera detector. But water vapor in a persons breath reacted with the superoxide layer, eliminating it and restoring the camera sensor so it worked normally.
"Years later, when looking at the Viking data, there was a flash of recognition" superoxide may be the oxidant on Mars, Hecht said.
Pasadena bureau chief Andrew Bridges contributed to this story.
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