Perchlorate On Mars, Preliminarily

MARTIAN SOIL SAMPLES dug from trenches beside NASA's Phoenix lander spacecraft appear to contain perchlorate ions, a finding that has both surprised and delighted mission scientists.

On Earth, perchlorate (ClO₄^–) is used in rocket fuel and has recently made headlines as a contaminant in both food and drinking water. Its presence on Mars, however, is seen as largely benign: It's stable in water, can act as a desiccant, and is not particularly inhospitable to organisms.

"This is an important piece in the puzzle to determine whether habitable conditions existed," said Peter Smith, principal investigator for the Phoenix mission, at a press conference on Aug. 4.

The researchers cautioned that the results are still preliminary and that they're announcing them ahead of peer review and publishing processes because of "extreme interest" in the mission and rampant "speculation on the Web" about Phoenix's discoveries, Smith said.

Phoenix contains four wet chemistry beakers, which are laden with ion-selective sensors. Samples have been delivered to two of these beakers since the craft began its mission on May 25. Both samples contained perchlorate ions, the scientists said. Whether the perchlorate ions are paired with magnesium, sodium, or ammonium ions, scientists don't know yet and analyzing results will take awhile, they emphasized. "This could potentially keep a lot of graduate students busy for a long time," team scientist Michael Hecht said.

Scientists also noted that Phoenix's other major suite of chemical detectors, the thermal gas emission analyzer (TEGA), has not yet confirmed perchlorate. Samples from other locations have been delivered to small ovens on the craft where they've been heated to temperatures of up to 1,000 ºC. Any evolved gas would be detected by a mass spectrometer. However, that instrument didn't detect evolved chlorine.

"We have much more work to do," said William V. Boynton, head of the TEGA team, at the press conference.

Smith also attempted to put brakes on the excitement. "Let the science team share their results at the proper pace," he said.