Test tubes containing methanogens, methane-producing microorganisms, line the shelves of Tim Kral's laboratory. Kral has successfully grown the microbes under some of the conditions found on Mars.

Above top, University of Arkansas researchers hope to directly study rocks from the Red Planet one day. In the meantime, they continue to examine the possibilities of the planet's history from the standpoint of what is known about earth. Above bottom, Harsh conditions on the surface of Mars seem to rule out the possibility of life. It's still possible, Kral contends, that life could occur below the surface, assuming limited water conditions.

Biology professor Tim Kral extracts methanogens from a solution, then injects them into test tubes in an anaerobic chamber. Methanogens thrive under harsh conditions, and Kral's experiments examine how the microbes grow under Mars-like conditions.

Alien Enviroment:

Searching for Life on Mars

By Melissa Blouin

University of Arkansas researchers work to unlock the Red Planet's secrets

Imagine life on a planet with a temperature so cold you would freeze in minutes, while the high radiation levels would fry your skin at the same time. You couldn't breathe without an oxygen mask, because carbon dioxide is almost the only gas around, and walking would be impossible because of the thin atmosphere and low gravity.

Welcome to the surface of the planet Mars. With a pressure at 0.6 percent that of the Earth's surface, an average temperature of -60 degrees C and an atmosphere of 95 percent carbon dioxide, it seems like a harsh, barren, lifeless world. Despite its hostile environment, scientists have long thought Mars the most likely candidate in the solar system for possible life, according to University of Arkansas chemistry professor Derek Sears.

"We see evidence that the atmosphere was once very different from what it is now," Sears said. "It's hard to believe that life didn't form at some point in the history of Mars."

Mars, the fourth planet from the sun, named for the god of war and discord, is the closest planet to our own. Its history appears to be similar to that of Earth in terms of volcanic activity and meteorite impacts. The days have similar lengths, and the planet is sometimes bathed in clouds and fog. Mars' pockmarked surface tells of a history of bombardment and volcanic events. It also displays evidence of old oceans, carved canyons, islands and vast river beds, which may once have contained tons of water, Sears said.

However, the Viking voyages to Mars in the 1970s found no evidence of organic life, or liquid water, on the planet's surface. The hope of finding life on Mars seemed to die with the lack of carbon-based life forms and the brutal conditions on the planet's surface.

But over the past two decades, notions of the tree of life have changed drastically. Scientists used to believe that life originated in an oxygen-rich environment, but they have found increasing evidence that life started under anaerobic conditions.

Armed with this new look at life's origins, biology professor Tim Kral has turned his microscope toward the interior of Mars to search for life beneath the rocky terrain.

A journey below Mars' surface takes speculation, but researchers assume the pressure and temperature rise as you go closer to the planet's center. This leads to the possibility of liquid water -- and therefore life -- somewhere below the surface. Any organisms found there, however, would have to survive without organic matter or oxygen.

Kral began his search for likely candidates on Earth by looking at extremophiles, microorganisms that live in the bottom of the ocean or in the cone of a volcano, among other places. He focused his attention on methanogens, methane-producing microorganisms from a group of microbes called Archaea, thought to be one of the most ancient branches on the tree of life. Although people have labeled these organisms "extreme," human beings and other oxygen-loving creatures actually deserve that title, Kral said. Archaea and other anaerobes comprise most of the biomass on Earth.

"Oxygen-liking life is on a limb of the tree of life. Anaerobic organisms form the trunk," Sears said.

Kral knew methanogens could survive extreme temperatures and thrived in an anaerobic environment. So he and graduate student Curtis Bekkum designed a series of experiments to see if methanogens could grow under some of the conditions found below the surface of Mars.

The researchers created a biological model of what life on Mars might be like based on what is known about the Martian landscape.

"There's nothing from Mars for us to work with," Kral said. "So you have to play the game from the standpoint of Earth."

To grow methanogens under some of the conditions found on Mars, Kral and Bekkum used ash from Hawaiian volcanoes -- known to share chemical characteristics with Mars soil. They also used carbon dioxide, hydrogen and limited amounts of water while growing the microbes in test tubes.

The methanogens grew successfully in the Mars soil simulant, obtaining all the macro and trace minerals they needed to survive, and they even grew with a limited water supply. Kral and Bekkum presented their results at the 1999 American Society for Microbiology meeting in Chicago.

Using large, black, rubber gloves and peering through a plastic window, Kral and Bekkum drew washed methanogen cells from a buffer solution and injected them into soil-filled test tubes inside an anaerobic chamber. They stored the sealed test tubes at different temperatures and checked them for methane production and hydrogen uptake -- two measures of microbe health. At any given time Kral has 100 methanogen test tubes in the lab, and each experiment takes anywhere from three weeks to two months.

Kral and his graduate students are currently removing small amounts of water from the methanogen test tubes to see if the organisms will adapt to life with less water.

Kral also plans to change the methanogen's energy source from hydrogen to carbon monoxide, which is known to be found in the atmosphere of Mars. "This is a hodgepodge of things that come together and tell a story," Kral said.

Kral said scientists can extrapolate research like this to search for life on Mars.

"When you're looking for life there -- what do you look for?" he said. "If you have an idea of what life might look like, you may form better ideas about where to look."

Scientists seeking signs of extraterrestrial life outside the solar system have debated about what chemical signals to look for in space. Methane may be one of the signatures they should seek, Kral said.

"If they find methane, there would be a reasonable chance that it would be produced by organisms," he said.

Kral's research on Earth can go at least one step beyond the test tube to a larger environment.