Sci tues
As NASA struggles to refocus its Mars program on the heels of two failed missions, one supremely logical mantra has emerged to guide the search for Martian life:
Follow the water.
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Great advice. But hard to heed on such a dry and dusty planet. No matter how much water might once have flowed on Mars, the place now looks downright dead. Liquid water, if it exists, might be a mile deep or more, scientists say.
But there are two places where water is known to exist in mass quantities, right at the surface: The polar caps.
Though summer melts a thin layer of carbon dioxide frost at the poles, a thick layer of mostly water ice remains. At the north pole, the permanent ice cap is larger than Texas and more than a half-mile (1 kilometer) thick.
Little critters, lathered in natural sunscreen and swathed in biological antifreeze, could be lurking just a few feet under the ice, scientists say. These microscopic Martians might hibernate for months or even thousands of years, waiting for a brief thaw, a personal spring vacation, a chance to go forth and make more Martians. Other life could be doing the backstroke, or whatever microbes do in their spare time, in languid pools of water melted by subsurface volcanic activity, all just a few yards down.
Though they might sound a bit like fish tales, these ideas are growing in popularity among scientists who have explored similar extreme environments, and the so-called extremophiles that inhabit them, on Earth. In the permafrost of Siberia, for example, a species of moss was found dormant but alive after 40,000 years.
"Life survives and even thrives in a variety of icy microhabitats in Earth's polar regions," says Warwick F. Vincent, a professor of biology at Laval University in Canada. He and his colleagues recently discovered bacteria and even more advanced life in pockets of water below the icy surface of the Arctic. Others have found evidence for life in similar subglacial lakes in Antarctica.
An obvious question follows for anyone interested in finding life on Mars:
"If we're following the water ... why is there not a heavy search in the areas where we know there is water ice?" wonders Meredith Payne, an Arizona State University researcher.
The next robots that will explore the surface of Mars, one from the European Space Agency and a pair from NASA, are planned for 2003 and 2004 but are not targeting the polar regions.
The search begins
So Payne has begun looking from her terrestrial vantage point.
She's working with Jack Farmer, a professor of geology and director of the ASU's astrobiology program, to examine Viking and Mars Global Surveyor satellite photographs of the fringes of the north polar ice cap of Mars. They look for places where there might be water, and hence possibly life, below. And they think they have some good candidate locations scoped out.
Payne and Farmer hunt for signs of underground volcanic activity that might have warmed overlying ice to create a subsurface lake. The lakes would sit in what's called a caldera, a cavity in the top of a volcano that's shaped like an inverted cone.
The signs of possible water could take other forms, such as telltale patterns that indicate huge flows of water pushed by lava.
"When a subglacial volcano erupts, a catastrophic outflow often ensues," Payne said. "Water rushes down at thousands of meters per second and takes sediment down with it." The result, seen in satellite images of Iceland, are alternating bands of light and dark.
Scientists have not determined whether Mars is still volcanically active, so Payne and Farmer might see signs of recent activity or they might find evidence of volcanism that is decades or centuries old. But ongoing underground volcanism might still provide a warm oasis today below the ice, while not necessarily erupting to the surface.
For now, the researchers have confined their search to the fringes of the ice cap, where the features are easier to spot than farther north where the ice is thicker. The fringes, along with the rest of the cap, are covered each Martian winter by a layer of frozen carbon dioxide, but in summer the features are either uncovered or easier to see through the thin water ice that remains.
"It might be possible to find extant life," Payne said, but that would depend on whether an ongoing volcanic heat source had kept water in liquid form over long periods of time. While it's not known how deep any potential life might exist in a subglacial volcanic lake on Mars, the possibilities range from just a few yards (or meters) to a half-mile (1 kilometer) or more, Payne said.
There might also be places that used to support life in subglacial volcanoes, but where all the ice has since melted away, potentially exposing a bed of fossils. And even a fossil would prove that ET at least did exist.
Cheers from the north
"This seems like a great place to focus the search for life," said Vincent, the Canadian biologist, when informed of the study. And he should know.
Vincent and his colleagues found "a rich community of microbes" growing in meltwater pockets in and on a 115-foot-thick (35 meters) shelf of ice that juts out into the Arctic Ocean.
"The microbes are deep-frozen and dormant through most of the year and then spring to life when meltwater forms around them for just a few days to weeks in the warmest years," Vincent said.
The frigid community is made up mostly of primitive creatures called cyanobacteria, which live in tightly-woven groups called microbial mats. The microbes produce chemicals that act as anti-freeze and UV shields, protecting them from frigid temperatures and from sunlight, which is known to pass relatively easily through water ice.
The chemical sunscreen in the microbial mat offers protection for other creatures, too, and the cyanobacteria can serve as a source of food for higher forms of life that otherwise wouldn't survive the harsh conditions. "We have even found multicellular animals such as flatworms growing in these microbe-protected environments," Vincent said.
Overlying ice insulates the microhabitats, providing additional protection against air temperatures that drop below minus 58 degrees Fahrenheit. Also, salts in the water lower the freezing point.
Vincent said material in geothermal fluid that might penetrate the ice cap of Mars "would have a similar antifreeze effect."
Next Page: First Iceland, then Mars
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