SEATTLE — The soil on Mars may be more capable of supporting life than previously thought, a new study suggests.

Researchers have long suspected that the martian surface is packed full of oxidizing compounds, which could make it difficult for complex molecules like organic chemicals — the building blocks of life as we know it — to exist. But the new study, which analyzed data gathered by NASA’s Mars Phoenix Lander, suggests that is not the case.

“Although there may be some small amounts of oxidants in the soil, the bulk material is actually quite benign,” said lead study author Richard Quinn of NASA’s Ames Research Center and the Search for Extraterrestrial Intelligence (SETI) Institute, both in Mountain View, Calif. “It’s very similar to moderate soils that we find on Earth.”Astrobiologists have long been interested in characterizing soils on Mars, to help determine whether life could ever have gotten a foothold on the red planet.

NASA’s $420 million Phoenix mission has given them a lot to ponder in this regard. The Phoenix lander touched down near the martian north pole in late May 2008, then made a variety of observations for the next five months.

Phoenix is most famous for confirming the existence of water ice on Mars, but it also made a lot of interesting soil measurements. One of those was the Mars dirt’s acidity, or pH, level.

“People really didn’t know what the pH was going to be,” Quinn said. “A lot of people believed that the soils would be very acidic.”

But just a month or so into its mission, Phoenix found that the dirt at its landing site was mildly basic, with a pH around 7.7. The lander also detected several chemicals that could serve as nutrients for life-forms, including magnesium, potassium and chloride.

These discoveries intrigued scientists, suggesting that martian soil is perhaps more hospitable to microbial life than they had thought. And the new results provide further evidence along those lines.

Phoenix made the pH and various other discoveries using its onboard wet chemistry laboratory (WCL). The lander scooped martian dirt into cups of water brought from Earth, and the WCL instrument analyzed the resulting solution.

Quinn and his colleagues studied the Phoenix data from 2008, focusing this time on measurements of martian soils’ oxidation-reduction potential. Oxidation refers to the stripping away of electrons. It is a destructive process that can tear up complex molecules like DNA, which is why people need antioxidants as part of a balanced diet.

Scientists had reason to think that martian soil might be highly oxidizing, Quinn said. In the mid-1970s, for example, NASA’s Viking landers mixed some organic compounds into martian dirt, and the chemicals appeared to decompose.

And Phoenix itself detected a molecule called perchlorate, which under some conditions is a strong oxidizer. But the new results, reported last month in the journal Geophysical Research Letters, paint a rosier picture of martian soil as far as habitability is concerned.

“When you look at the composite of all the material in there, and you measure the overall reactivity of that soil in solution, it’s comparable to what you would find in terrestrial soils, Earth soils,” Quinn said. “So it’s not an extreme environment in that regard.”

The results do not prove that martian life exists or ever has existed. However, they and other recent finds — including evidence from the High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA’s Mars Reconnaissance Orbiter that liquid water may have flowed just beneath the martian surface in the last year or so — are making scientists more and more hopeful.

“The evidence from the HiRISE team that there may be seasonal water flow at some locations, combined with this measurement that shows that when the soil is wetted it’s actually not harsh conditions — it’s very positive in terms of the potential for life to get a foothold,” Quinn said.