An Icy Dig in Search of Signs of Life on Mars

The mission is not designed to find life itself -- except in the highly unlikely event that it is large and visible via camera -- because the process of testing for organic materials will destroy the samples to the point that life forms would not be identifiable. Instead, Phoenix will investigate whether the conditions for life exist. The search involves two sets of chemistry experiments: testing for carbon-based organic compounds created by biological or chemical processes, and testing for inorganic minerals that make life possible.

"If we can find nitrates, carbonates and the like in the soil, then we'll know the planet is much friendlier for life," said Samuel P. Kounaves of Tufts University, lead scientist for the inorganic experiments. "These minerals have been missing in all the Mars missions, but they should be there. We think they may well be below the surface, where they're protected from the [ultraviolet] rays that bombard the planet."

Carbon, in particular, has been missing in action. Although carbon dioxide fills Mars's atmosphere and carbon has been found in meteorites from the planet, the element has never been detected on the surface.

The last time that a Mars mission looked specifically for chemical signs of life was in 1976, when two Viking spacecraft landed. To the disappointment of planetary scientists, neither found any organic material.

Nonetheless, Smith is optimistic that landers can eventually be able to find signatures of life on Mars, if they exist. He said he recently spoke with a researcher who removed a cubic centimeter of ice from a long-frozen Siberian lake and found DNA remnants from a wide variety of life forms.

"It's amazing how much organic material gets frozen in ice," Smith said. "They didn't find DNA from every creature, but they were able to build the basic tree of life from that one cubic centimeter."

The solar-powered Phoenix is expected to function for about three months. If it finds signs of organic material and nutrients, the Mars Science Laboratory -- with a much larger and more sophisticated rover, scheduled for launch next year -- may be sent to a similar site. The European Space Agency is planning a lander, the Exo-Mars, for 2013, to search for signs of past or present life.