New test results coming in from the Phoenix Mars Lander suggest that Martian soil may not be so akin to Earth's after all.

A little over a month after NASA scientists announced that they were finding more familiar than alien elements in the soil on Mars from test results sent back by the Lander, researchers now have discovered evidence that that might not be the case after all. They're also double-checking to make sure that the Earth-like elements found by Phoenix on the northern pole of Mars weren't actually brought from Earth and deposited there when the Lander touched down.

"We are committed to following a rigorous scientific process. While we have not completed our process on these soil samples, we have very interesting intermediate results," Peter Smith, Phoenix's principal investigator, said in a written statement released Tuesday. Smith, who is a senior research scientist at the University of Arizona, added that while the initial analyses from the wet chemistry laboratory onboard Phoenix suggested that Martian soil was like that of Earth, "further analysis has revealed un-Earthlike aspects of the soil chemistry."

NASA planned to hold a press conference at 2pm US EDT Tuesday to discuss the findings from the Mars research. In information sent out prior to the press conference, NASA noted that previous tests, including one done in the wet chemistry lab on Phoenix, showed the presence of perchlorate, which is described as a highly oxidizing substance. However, this week, the analysis ovens onboard the Lander sent back new information showing that no evidence of perchlorate was found in a sample taken directly above the ice layer on Mars.

Perchlorate can be found on Earth as both a natural and a man-made contaminant. According to the California Department of Toxic Substances Control, the compound is used as an ingredient in solid fuel for rockets and missiles. Perchlorate-based chemicals also are used to build fireworks, pyrotechnics and explosives. "Perchlorate is becoming a serious threat to human health and water resources," the department says on its Web site.

NASA scientists are working to figure out if the Mars Lander could have contaminated the testing area when it landed, or if Phoenix's testing instruments could have contained biological contaminants. "When surprising results are found, we want to review and assure our extensive pre-launch contamination control processes covered this potential," Barry Goldstein, the Phoenix mission's project manager, said in a statement.