Martian Soil Gets Baked | Chemical & Engineering News
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Web Date: June 18, 2008

Martian Soil Gets Baked

Gas analyzer heats sample dug by Phoenix lander
Department: Science & Technology
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ICE CACHE?
The white material in the upper portion of this 2- to 3-inch-deep trench, dug on June 12 by Phoenix's robotic arm, could be ice or salts.
Credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University
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ICE CACHE?
The white material in the upper portion of this 2- to 3-inch-deep trench, dug on June 12 by Phoenix's robotic arm, could be ice or salts.
Credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

After three weeks of flexing its mechanical joints on the surface of Mars, the Phoenix lander is doing some science. The soil sample scooped by the probe's robotic arm has not yet yielded any surprises—it contains carbon dioxide, but no water, for example—but the analyses are just beginning, mission scientists say.

The testing finally began after a few tense days during the week of June 8, when engineers worked to coax a clumpy scoop of martian dirt into one of eight ovens on the probe. There, the soil is undergoing cycles of increased heating, and evolved gas will then be analyzed by a mass spectrometer.

The goal of the mission is to study the possible ancient role of water near Mars's north pole, a region where NASA's Mars Odyssey spacecraft detected fields of subsurface ice several years ago.

Images from Phoenix show a stark white substance about 5 cm down in the trenches dug by the scoop, which scientists say could be salts, but they favor the possibility of ice, said William V. Boynton, head of the team for the craft's thermal and evolved-gas analyzer (TEGA), at a press briefing on June 16.

That no water has been found so far in the sample now being analyzed is to be expected, Boynton said. Because the sample sat uncovered in the martian environment for days, any water ice it contained would have sublimated into the planet's tenuous atmosphere. And the carbon dioxide detected by TEGA had likely long been absorbed from the atmosphere by the soil grains and then released after heating.

When the sample is eventually heated to 1,000 °C, over the next few days, scientists could possibly detect sulfur dioxide, a product of the decomposition of sulfate minerals that would likely have formed in an ancient aqueous environment. "The temperature at which gases are released is a fingerprint that tells us the nature of that mineral," Boynton said.

Within the next two weeks, using Mars-worthy beakers that contain premeasured reagents, Phoenix will examine soil samples for the presence of ions such as nitrate and chloride or metals such as lead and copper.

Raymond E. Arvidson, earth and planetary sciences professor at Washington University, in St. Louis, and coinvestigator for the lander's robotic arm, said the team will continue to take images of the white substance uncovered by Phoenix over the next few days. If it is isolated ice, it should gradually disappear as it sublimates, he said.

The $460 million Phoenix mission is the first in NASA's planned series of relatively low-cost exploratory Mars Scout missions as the agency prepares for eventual human exploration of the planet.

 
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