The National Aeronautics and Space Administration said two samples analyzed by the spacecraft's Microscopy, Electrochemistry and Conductivity Analyzer, or MECA, suggest one soil constituent might be perchlorate, a highly oxidizing substance.

Researchers had been waiting for results from the Thermal and Evolved-Gas Analyzer, or TEGA, which also is capable of detecting perchlorate, NASA said. But the results from 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," said Peter Smith, Phoenix's principal investigator at the University of Arizona-Tucson. "While we have not completed our process on these soil samples, we have very interesting intermediate results. Initial MECA analyses suggested Earthlike soil. Further analysis has revealed un-Earthlike aspects of the soil chemistry."

Since landing May 25, Phoenix has been studying Martian soil with MECA's wet chemistry lab, two microscopes, a conductivity probe, TEGA's ovens and two cameras.