By Senior space writer
updated 3/9/2004 3:12:01 PM ET 2004-03-09T20:12:01

If you’ve got a nose for news, here’s a bulletin: Mars may smell to high heaven.

Recent revelations about the red planet from NASA’s two Mars exploration rovers -- Spirit and Opportunity -- have relayed back details about the volcanic and water-laden landscape.

For example, at the Meridiani Planum site in which the wheeled Opportunity now roves, the robotic field geologist found a very high concentration of sulfur. The chemical form of this sulfur appears to be in magnesium, iron or other sulfate salts.

Using its science gear, the robot has detected a hydrated iron sulfate mineral called jarosite.

On Earth, rocks with as much salt as this Mars rock either have formed in water or, after formation, have been highly altered by long exposures to water. Jarosite may point to the rock's wet history having been in an acidic lake or an acidic hot springs environment.

Sulfur, acids, magnesium, iron -- all put together under the carbon dioxide-rich skies of Mars -- could just reek.

Eye of the smelling beholder
"You have sulfur and you have oxidizing environments…you make the sulfate. And then if you end up with some acid-favoring situations, like acid groundwaters, you make sulfuric acid. Out of that comes hydrogen sulphide as a byproduct in some reactions…and you start to stink," said Jim Garvin, NASA Lead Scientist for Mars and Lunar Exploration in Washington, D.C.

Garvin said on his field excursions here on Earth to volcanic areas, the sulfurous stench to him is a kind of cleansing smell. "I don’t know. It may stink in the eye of the smelling beholder," he told SPACE.com .

While the aroma of Mars might not be daunting for robots, knowing more about how that environment appeals to future human explorers is serious business.

Unpleasant odor
For one, hydrogen sulphide (H2S) is a gas encountered worldwide here on Earth. Drilling formations with the presence of H2S can encounter some very serious problems. While it gives off an unpleasant odor and can stir up a headache, it is also explosive and poisonous.

No doubt future Mars explorers tromping about the red planet will be well-suited to work outside their habitat. But precautions must be taken.

Humans on Mars don’t have to look back too far in the space exploration journals to take note of what Apollo moonwalkers encountered.

After bouncing about on the Moon and crawling back into their lunar module, several Apollo astronauts noticed they had tracked back into their home-away-from-home rock and dust particles. In doffing their helmets, the smell was likened to wet ashes in a fireplace, even spent gunpowder from a just fired shotgun.

If Mars is to be home base for 21st century astronauts, much more data about the planet is necessary before humans set foot, and nose, on that faraway world.

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