New results from NASA's Phoenix Mars lander suggest that the surface layers of the Martian arctic region may not be as friendly to life as initial results suggested, NASA said today.

Two samples analyzed within the last month by Phoenix's Microscopy, Electrochemistry and Conductivity Analyzer (MECA) suggest that the Martian dirt may contain perchlorate, a highly oxidizing substance, which would create a harsh environment for any potential life.

The findings stand against the results from MECA's first analysis, which indicated the dirt was Earth-like in certain respects, including its pH and the presence of certain minerals.

"Initial MECA analyses suggested Earth-like soil. Further analysis has revealed un-Earthlike aspects of the soil chemistry," said Phoenix principal investigator Peter Smith.

The news came today on the heels of a report on Friday that MECA had found intriguing results that had been shared with the White House. In correspondence with SPACE.com, Smith denied that any briefing with the White House had been held.

And the findings are inconclusive as yet, Smith indicated. "We are committed to following a rigorous scientific process," he said. "While we have not completed our process on these soil samples, we have very interesting intermediate results."

NASA will hold a press briefing tomorrow to further discuss the new MECA findings.

The Phoenix team had been waiting for results from Phoenix's Thermal and Evolved-Gas Analyzer (TEGA) to see if it also detected perchlorate in dirt samples. TEGA's tiny ovens heat the samples and then "sniffs" the vapors given off to determine their composition.

Sunday's TEGA experiment, which analyzed a sample taken directly above the ice layer, found no evidence of perchlorate.

"This is surprising since an earlier TEGA measurement of surface materials was consistent with but not conclusive of the presence of perchlorate," Smith said.

The team is working to rule out the possibility that the perchlorate readings could be contamination brought from Earth.

"When surprising results are found, we want to review and assure our extensive pre-launch contamination control processes covered this potential," said Barry Goldstein, Phoenix project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

MECA's wet chemistry laboratory mixes samples of Martian dirt with water brought from Earth. Sensors on the inner surface of the beakers act like electronic tongues and "taste" the dirt to detect salts that can dissolve in water. The sensors can also detect the pH of the surface.

All of this information gives scientists a picture of what the surface layer of dirt looks like now and whether or not it might have been a habitable area at some point in the planet's past.

MECA's first analysis showed that the Martian regolith contained several soluble minerals necessary for life, including potassium, magnesium and chloride. The surface also had an alkaline pH, which on Earth is suitable for growing some plants, such as asparagus.

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