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October 27, 2003
Hunting for Martians
Was there -- is there -- life on Earth's closest neighbor? Berkeley Lab Earth scientists hope to home in on the answer. (Image: NASA)  

If life ever existed on Mars, it'll take more than luck to find it on a planet nearly twice the size of the moon. The vestiges of biological activity could be underground, inside rocks, or strewn about the surface. They could be near the red planet's icy poles, or somewhere along its equator.

To narrow the search, a team of scientists that includes five Berkeley Lab Earth Sciences Division researchers will explore what it takes to sustain primitive life -- and then determine if, when, and where these conditions arose on the red planet. Thanks to a five-year, $5 million grant from NASA's Astrobiology Institute, the team will analyze Mars's natural history, study arid regions on Earth that mimic the Martian landscape, and investigate exotic microbes that thrive in extreme environments.

"Ultimately, we want to determine if life evolved elsewhere in the universe," says principal investigator Jillian Banfield, a professor in the University of California at Berkeley's Department of Earth and Planetary Science. She leads a team of ten researchers that includes fellow Lab researchers Kristie Boering, Donald DePaolo, William Dietrich, and Michael Manga, all of whom are also Department of Earth and Planetary Science professors. "We chose Mars because it's relatively accessible, and it may have possessed the ingredients necessary for life."

Although many scientists suspect conditions on Mars are currently too harsh to sustain life, except maybe deep underground, they also suspect the planet once harbored life's prerequisites. The Martian landscape is riddled with canyons that were possibly carved by ancient rivers. And, perhaps long ago, a robust atmosphere protected the surface from harmful ultraviolet radiation. The planet was never lush -- far from it -- but it may have been hospitable enough to give life a tiny foothold. And as more and more strange microbes are discovered on Earth, such as extremophiles that live inside basalt, the possibility that a few hardy microbes called Mars home becomes more plausible.

The trick is finding the microscopic mess they left behind, and this involves an ever-narrowing search for life's calling cards. A good start is water, the bath in which biochemical reactions occur. Manga and Dietrich will study the evolution of the Martian hydrosphere. Did magma-melted ice unleash rivers? And is water trapped in the soil today? Solving these puzzles could reveal regions most likely to yield life.

Millions of years ago, Mars may have hosted rivers and lakes like those depicted in this artist's rendition. (Image: NASA/JPL, Corby Waste)

The early Martian atmosphere poses other questions. In her lab, Boering will investigate whether a sun-induced chemical haze ever shielded the surface from ultraviolet radiation. This same haze could have also regulated Mars's surface temperature, providing still more clues as to the conditions faced by microscopic Martians.

The team will also study several sites in the cold desert that straddles the Oregon-Idaho border. Some sites were chosen because they mirror the Martian topography. The sinuous Box Canyon, which drains into Idaho's Snake River, is a dead ringer for the channels of the Nirgal Valles on Mars. Did the same groundwater-driven erosion that created Box Canyon also create its Martian twin? And if so, did this water support life?

Other sites were chosen because they host microbial ecosystems that could also live on Mars. A mine in California's Iron Mountain boasts a flourishing population sustained not by photosynthesis but by sulfur and iron oxidation -- common elements in Martian geology.

In addition to zeroing in on where to look, they'll also determine what to look for. Isotopic changes are one such biosignature. Unlike inorganic phenomena such as sedimentation and volcanism, organisms change the proportion of certain isotopes when they metabolize energy. More specifically, lighter isotopes of elements such as calcium and iron gradually outnumber heavier isotopes as they make their way up the food chain. A bird's bones possess more calcium 40 than calcium 48 relative to the calcium in its diet, and if a person eats the bird and uses its calcium to make bone, that person's calcium is lighter still.

The 1997 Pathfinder mission found a cold, arid planet. Future missions will require more advanced sensors to detect microscopic biosignatures.
(Image: NASA)

Using mass spectrometry, DePaolo will look for this fractionation in a slew of Martian meteors housed at the Johnson Space Center and museums. He'll also learn how extremophiles here on Earth leave behind fractionated isotopes, an inquiry that could someday help detect the remnants of microbial life in Martian rocks.

"If we see fractionation in Martian meteors or rocks, it would be difficult to explain without biological activity," DePaolo says.

To pinpoint other types of biosignatures, Banfield will investigate how mineral surfaces change when exposed to biologically produced compounds. She'll also characterize how entire microbial communities, not just individual organisms, leave telltale mineralogical and isotopic records.

The team will also test ways to detect these biosignatures using remotely operated sensors, an initiative that could lead to the development of robots that roam Mars and hunt for life's signs.

"We need to determine how robots can conduct biogeochemical measurements in the field, and what they should search for," Banfield says.

"Our work will hopefully inform a future mission," adds DePaolo. "We'll take what we know about robotics, earth's hydrology, planetary formation, and Mars in particular — and narrow the focus concerning where life could have existed."

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