Perchlorate found in Martian soil
New soil chemistry tests by NASA’s Phoenix Mars lander have unexpectedly uncovered evidence of perchlorate, a highly reactive salt found naturally on Earth and used in a variety of products, including fertilizer, fireworks and rocket fuel, scientists said Tuesday.
The finding has surprised scientists evaluating results from Phoenix, but they denied that the presence of large amounts of the salt would render Mars uninhabitable.
“It might even be a positive” indicator for habitability, said Peter Smith, one of the lead scientists on the Phoenix mission.
On Earth, perchlorate is found most abundantly in the surface soils of Chile’s Atacama Desert, which coincidentally has long served as a Martian stand-in for researchers trying to understand conditions on the Red Planet.
The 600-mile-long strip of land in Chile is about 50 times drier than Death Valley. Even so, it is not uninhabited. Microbes flourish there, and some life forms even feed on the perchlorate in the soil.
“This is an important piece in the puzzle” surrounding Mars and its ability to sustain life, Smith said at a media briefing in Tucson, where much of the Phoenix research is based at the University of Arizona.
“In itself, it’s neither good nor bad for life,” he said.
Perchlorate was first detected several weeks ago with Phoenix’s onboard wet chemistry lab, which mixes water from Earth with Martian soils.
The scientific team held back the information while researchers tried to confirm the finding with a second onboard instrument, known as the thermal and evolved-gas analyzer, which can heat the soil up to 1,800 degrees Fahrenheit to determine its exact chemical composition.
Those tests remain incomplete, but NASA decided to publicize the perchlorate discovery Tuesday after word spread that the agency was hiding evidence that Mars was hostile to life. The scientists Tuesday denied that they were being secretive, saying they simply wanted to consult with other scientists before publicizing the data.
Researchers said they were initially startled by the size of the chemical signal. Because it was so large, they at first discounted it, thinking the instrument had developed a problem. Some scientists thought the device might even be picking up contamination from the rocket engines that carried Phoenix across 200 million miles of space from Earth to the vast, rolling northern plains of Mars.
But on Tuesday, the scientists tended to discount contamination because the craft’s descent engines use hydrazine, not chlorine. Also, no perchlorate was found when Phoenix calibrated the wet chemistry lab after its landing May 25 on the Red Planet.
The wet chemistry lab is a set of four beakers into which water is injected to mix with the soil. A collection of 26 sensors then samples the mixture to analyze its contents.
Because perchlorate is so soluble in water, it is rarely found in surface soils on Earth. Even though Phoenix is sitting atop a vast underground sheet of hard-as-concrete ice, it hasn’t rained on Mars in billions of years.
As well as confirming the wet chemistry finding with the TEGA instrument, the scientists are trying to understand the mechanism that could deposit such large amounts of perchlorate on the surface.
The only other chemistry done on Mars was by the twin Viking landers in the 1970s. They found possible evidence of peroxide, a very different compound.
Because Phoenix is stationary, it won’t be possible to determine how widespread these varieties of soils are. That must wait for the giant Mars Science Lab, scheduled for launch in 2009.
john.johnson@latimes.com
