Digging Deep on Mars

Mars mission: The Phoenix Mars Lander is scheduled to launch on Saturday from Cape Canaveral and land near the red planet’s north pole next May. It will perform unprecedented experiments on soil and ice and monitor the planet’s climate.
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A NASA spacecraft preparing to launch will use novel technology to search for signs of life on the red planet.

Thursday, August 2, 2007
By David Chandler

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A new Mars spacecraft called Phoenix, created largely from leftovers from one mission that failed and another that was canceled, is set for takeoff on Saturday from Cape Canaveral, and it could provide more information than ever before about just what Mars is made of.

In particular, the red planet's enigmatic, highly reactive soil is about get its first in-depth investigation, and may finally give up its secrets--particularly whether it does, or once did, hold life--after Phoenix lands in a previously unexplored area near Mars's north pole next May.

Phoenix is equipped with a trenching tool that can dig down half a meter into the dirt--far lower than the few centimeters of previous missions--and a grinding tool that can penetrate even superhard ice. Phoenix carries a battery of instruments that go far beyond anything previously taken to another planet, including the most advanced weather station yet sent to Mars. It also carries two different kinds of microscopes: an optical microscope with its own multispectral light source, and an atomic-force microscope that can see details as small as 200 nanometers--one-hundredth the diameter of a human hair.

Both microscopes are capable of revealing details of soil structure never even glimpsed before, which may help bring to light important details about the past geology and climate of the planet. For example, the shapes of particles can reveal whether they were exposed to flowing water, or were repeatedly frozen and thawed, or remained soaking in water for extended periods.

The cameras and microscopes will study the freshly exposed surfaces, and then the really new science begins. Scoops of soil and ice will be picked up and analyzed by various devices, including a wet chemical lab that will dissolve particles and study their chemistry, and another device that will vaporize the soil and melt the ice to study the molecules within it.

This instrument, called the Thermal and Evolved Gas Analyzer, or TEGA, is capable of determining exactly how much ice is in the soil at various depths and the ratios of various isotopes, including hydrogen and its heavier form, deuterium. And if there are organic chemicals lurking in that ice, Phoenix could discover their presence on Mars for the first time and learn a bit about the details of their composition.

Organic molecules--any compounds containing carbon--constantly rain down on Mars, as they do on Earth, from meteors burning up in the atmosphere, which is why scientists were so startled when Viking didn't find any. A new analysis last year suggests that that failure may have been because the Viking instrument didn't heat its samples enough to detect certain kinds of "refractory" organics that might be there.

"If organics are present, we'll detect them," says Bill Boynton, a biochemist at the University of Arizona who led the team that developed the TEGA instrument. It works by putting a tiny scoop of soil into a chamber, sealing it shut, and then slowly heating it and measuring the vapors given off as the temperature rises all the way to 1,000 ºC.

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