FN - Arizona, US - The pervading carpet of perchlorate chemicals found on Mars may boost the chances that microbial life exists on the Red Planet — but perchlorates are also perilous to the health of future crews destined to explore that way-off world.

Perchlorates are reactive chemicals first detected in arctic Martian soil by NASA's Phoenix lander that plopped down on Mars over five years ago in May 2008.

It is likely both of NASA's Viking Mars landers in 1976 measured signatures of perchlorates, in the form of chlorinated hydrocarbons. Other U.S. Mars robots — the Sojourner, Spirit and Opportunity — detected elemental chlorine. Moreover, orbital measurements taken by the Mars Odyssey spacecraft show that chlorine is globally distributed.

And more recently, NASA's Curiosity rover found perchlorates within Gale Crater, where it landed in August 2012. [Missions to Mars: Robotic Invasion of Red Planet (Infographic)]

Finding calcium perchlorate "was one of our most unexpected results," said Peter Smith, the Phoenix principal investigator at the University of Arizona in Tucson.

"Perchlorate is not a common word in the English language; all of us had to go and look it up," Smith said during Spacefest V, a conference held May 24-27 in Tucson, Ariz. "Perchlorate has become an important component of the soil … and half a percent is a fair amount," he said.

Smith said microbes on Earth use perchlorate for an energy source. They actually live off highly oxidized chlorine, and in reducing the chlorine down to chloride, they use the energy in that transaction to power themselves. In fact, when there's too much perchlorate in drinking water, microbes are used to clean it up, he said.

Furthermore, seasonal flow features seen on Mars may be caused by high concentrations of the brines of perchlorate, which has a strong attraction to water and can drastically lower its freezing point, Smith told SPACE.com.

The high levels of perchlorate found on Mars would be toxic to humans, Smith said.

Any humans exploring Mars, Smith said, will find it hard to avoid the finest of dust particles. "It'll get into everything…certainly into your habitat."

Good news, bad news Perchlorate has made, and continues to make, the search for organics on Mars all but impossible, said astrobiologist Chris McKay of NASA's Ames Research Center in Moffett Field, Calif.

"Its presence is good news for the possibility of life on Mars…but very, very bad news for humans, McKay told SPACE.com. "Once again, Mars is full of surprises."