Swamp gas fuels Martian mystery
Scientists hope it's sign of microbial life
BY ROBERT S. BOYD
Washington Bureau
WASHINGTON - For years, scientists searching for life on other worlds
have concentrated on finding water. No creature on Earth, from whales
to bacteria, can live without it.
But now they are also pursuing another line of evidence - swamp gas.
Formally known as methane or natural gas, this common compound of
carbon and hydrogen is produced by decaying vegetation, in coal mines,
rice paddies and cows' stomachs, and by myriad tiny microbes called
methanogens. Even the world's trillions of termites pump out little
puffs of methane when they consume wood.
The recent discovery of trace amounts of methane on Mars stirred hopes
that it might be another signal that microbial life exists - or once
existed - on the Red Planet.
"We have clear evidence that there is a source of methane on Mars,"
said Michael Mumma, an astrobiologist at NASA's Goddard Space Flight
Center in Greenbelt, Md. "We're going to test this as a search for
other evidence (of life)."
The space agency and its European counterpart have scheduled an
international "Methane-on-Mars" workshop in May. They want to figure
out how to follow this tantalizing hint that the seemingly dead planet
might still be biologically active.
Interest in methane is high because this gas, a fragile compound of one
atom of carbon and four atoms of hydrogen, is easily destroyed by the
intense ultra-violet radiation raking the Martian surface.
Because methane's lifetime is short, scientists figure it must have
been created within the last 300 years, implying that life may still
exist - or very recently existed - on Mars.
"The presence of significant methane on Mars requires recent release
from sub-surface reservoirs," said Mumma, who discussed his findings at
an astrobiology conference in Boulder, Colo., in April.
There is a major problem, however. Although most of the methane on
Earth is generated biologically, a significant amount - perhaps as
much as 20 percent - comes from non-biological chemical reactions.
Volcanoes, the hot springs of Yellowstone National Park and hot-water
vents at the bottom of the oceans all produce quantities of methane.
Furthermore, huge amounts of non-biological methane are found on
gaseous planets like Jupiter and Saturn.
Frozen lakes of methane were detected this year on Saturn's moon,
Titan. Comets are full of it.
Since living creatures are not the only way to generate swamp gas,
scientists can't be sure how the Martian methane originated.
"We don't have a conclusion about its origin," Mumma admitted.
"Many different lines of evidence are going to be needed to convince
people that it's biological," said Stephen Mojzsis, a geologist at the
University of Colorado in Boulder.
Because of this uncertainty, Norman Pace, a University of Colorado
molecular biologist, warned researchers at the conference not to take
the traces of methane on Mars as proof of life.
"This is not the smoking gun," he said.
Jonathan Telling, a geologist at the University of Toronto, said
scientists might be able to distinguish between biological and
non-biological methane on Mars by testing the carbon and hydrogen atoms
in the gas. Each of these elements comes in a lighter and heavier form.
On Earth, the lighter forms are generated by living organisms, the
heavier ones by inorganic chemistry.
Presumably the same thing could happen on Mars.
Tullis Onstott, a geoscientist at Princeton University in New Jersey,
has developed a device to measure the heavier and lighter forms of
carbon and hydrogen in Martian methane. He wants to put his instrument
on a future Mars rover, hoping to determine whether the gas is
biological or non-biological in origin.
The Martian methane was detected in 2003 and 2004 by three separate
observatories - ground telescopes in Hawaii and Chile and a European
space satellite. It was coming from at least five different locations
on the planet.
The amounts were tiny - from 10 to 200 parts of methane per billion
parts of atmosphere - compared to an average of 1,500 parts per
billion on Earth. But that was enough to set off a new wave of
excitement among those seeking extraterrestrial life.
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