Martian soil may be less Earthlike and less hospitable to life than researchers believed.

NASA's Phoenix Mars Lander has found traces of perchlorate in two soil samples analyzed during the past month, the space agency announced today. The results appeared to be the same ones rumored this weekend by AviationWeek.com to have been seen by the White House and to reflect Mars's habitability for life.

Perchlorate, or ClO4, is a naturally occurring and man-made chemical that is the primary ingredient in solid rocket fuel, according to the EPA. Where such a contaminant might have come from is unclear. The fuel in the thrusters that Phoenix used to land on Mars was made of hydrazine, not perchlorate.

The presence of such a chemically reactive compound in Martian soil would seem to make that soil less supportive of life. Here on Earth, high doses of perchlorate can interfere with thyroid hormone production, which can harm babies in the womb.

Phoenix's MECA wet chemistry experiment detected the chemical. NASA said the Phoenix team was waiting for the craft's gas analyzer, TEGA, to confirm the finding. The agency said that results from a TEGA experiment on Sunday, which analyzed a sample take from directly above the soil's ice layer, did not detect perchlorate.

"This is surprising since an earlier TEGA measurement of surface materials was consistent with but not conclusive of the presence of perchlorate," Peter Smith, Phoenix's principal investigator at the University of Arizona, Tucson, said in the NASA statement.

NASA said the team is also working to confirm that the chemical was not a stow-away from Earth that crept into the instruments or the samples. The agency said it would provide further information tomorrow afternoon.