Saturday, June 28, 2008

Alkaline Soil Sample From Mars Reveals Presence of Nutrients for Plants to Grow


Stick an asparagus plant in a pot full of Martian soil, and the asparagus might grow happily, scientists announced Thursday.

An experiment on the Phoenix Mars lander showed the dirt on the planet’s northern arctic plains to be alkaline, though not strongly alkaline, and full of the mineral nutrients that a plant would need.

“We basically have found what appears to be the requirements, the nutrients, to support life whether past, present or future,” said Samuel P. Kounaves of Tufts University, who is leading the chemical analysis, during a telephone news conference on Thursday. “The sort of soil you have there is the type of soil you’d probably have in your backyard.”

Mars today is cold and dry, and the surface is bombarded by ultraviolet radiation, making life unlikely, but conditions could have made the planet more habitable in the past. Plants that like alkaline soil — like asparagus — might readily grow in the Martian soil, provided that other components of an Earth-like environment including air and water were also present.

The preliminary findings from Phoenix do not answer whether life ever existed on Mars (or might still exist somewhere underground), only that conditions, at least at this location, are not the harshest imaginable. The soil, taken close to the surface, was similar to what is found in parts of Antarctica, Dr. Kounaves said. The soil elsewhere on the planet could well be very different; even the soil farther down in the ground could turn out to be acidic or otherwise vary in composition.

The Phoenix is capable of performing the same chemical analysis on three more samples.

In a different experiment, a tiny oven heated another sample of the Martian soil to 1,800 degrees Fahrenheit, which released water vapor. “This soil clearly has interacted with water in the past,” said William V. Boynton of the University of Arizona, the lead scientist in this experiment.

Dr. Boynton said he could not say when the liquid water was present or even where it was. The moisture might have come from dust particles that had blown there from other parts of Mars. “At this point, it is difficult to quantify what was given off,” he said.

The oven experiment also found carbon dioxide vapors, not surprising because the planet’s thin atmosphere is primarily carbon dioxide. The data have not revealed any carbon-based compounds.

The Phoenix mission is not directly looking for life on Mars, but rather whether conditions for habitability ever existed. In the wet chemistry experiment, water was mixed into the soil to produce Martian mud. Then the apparatus performed the same sorts of tests that gardeners use to test the condition of their soil.

The pH level was between 8 and 9, Dr. Kounaves said. The pH, or potential of hydrogen, reflects the concentration of hydrogen ions, or acidity, of a substance and usually varies between 0 and 14, with 7 considered neutral. (The water of Earth’s oceans, for comparison, has a pH of 8.2.) The experiment also found the presence of magnesium, sodium, potassium and chloride ions in the soil.

“There’s nothing about it that would preclude life,” Dr. Kounaves said. “In fact, it seems very friendly.”