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Jan.
15, 2009: Mars today is a world of cold and lonely
deserts, apparently without life of any kind, at least on
the surface. Indeed it looks like Mars has been cold and dry
for billions of years, with an atmosphere so thin, any liquid
water on the surface quickly boils away while the sun's ultraviolet
radiation scorches the ground.
The
situation sounds bleak, but research published today in Science
Express reveals new hope for the Red Planet. The first
definitive detection of methane in the atmosphere of Mars
indicates that Mars is still alive, in either a biologic or
geologic sense, according to a team of NASA and university
scientists.
"Methane
is quickly destroyed in the Martian atmosphere in a variety
of ways, so our discovery of substantial plumes of methane
in the northern hemisphere of Mars in 2003 indicates some
ongoing process is releasing the gas," says lead author
Michael Mumma of NASA's Goddard Space Flight Center. "At
northern mid-summer, methane is released at a rate comparable
to that of the massive hydrocarbon seep at Coal Oil Point
in Santa Barbara, Calif."
Right:
An artist's concept of a possible geological source of Martian
methane: subsurface water, carbon dioxide and the planet's
internal heat combine to release the gas. [animation]
Methane
-- four atoms of hydrogen bound to a carbon atom -- is the
main component of natural gas on Earth. It is of interest
to astrobiologists because much of Earth's methane come from
living organisms digesting their nutrients. However, life
is not required to produce the gas. Other purely geological
processes, like oxidation of iron, also release methane. "Right
now, we don't have enough information to tell if biology or
geology -- or both -- is producing the methane on Mars,"
said Mumma. "But it does tell us that the planet is still
alive, at least in a geologic sense. It's as if Mars is challenging
us, saying, hey, find out what this means."
If
microscopic Martian life is producing the methane, it likely
resides far below the surface, where it's still warm enough
for liquid water to exist. Liquid water, as well as energy
sources and a supply of carbon, are necessary for all known
forms of life.
"On
Earth, microorganisms thrive 2 to 3 kilometers (about 1.2
to 1.9 miles) beneath the Witwatersrand basin of South Africa,
where natural radioactivity splits water molecules into molecular
hydrogen (H2) and oxygen (O). The organisms use
the hydrogen for energy. It might be possible for similar
organisms to survive for billions of years below the permafrost
layer on Mars, where water is liquid, radiation supplies energy,
and carbon dioxide provides carbon," says Mumma.
"Gases,
like methane, accumulated in such underground zones might
be released into the atmosphere if pores or fissures open
during the warm seasons, connecting the deep zones to the
atmosphere at crater walls or canyons," he says.
"Microbes
that produced methane from hydrogen and carbon dioxide were
one of the earliest forms of life on Earth," notes Carl
Pilcher, Director of the NASA Astrobiology Institute which
partially supported the research. "If life ever existed
on Mars, it's reasonable to think that its metabolism might
have involved making methane from Martian atmospheric carbon
dioxide."
Above:
This graphic shows one way methane is destroyed in the Martian
atmosphere: the molecules are rapidly broken apart by solar
ultraviolet radiation. Because methane doesn't last long in
the martian environment, any methane found there must be recently
produced. [animation]
However,
it is possible a geologic process produced the Martian methane,
either now or eons ago. On Earth, the conversion of iron oxide
(rust) into the serpentine group of minerals creates methane,
and on Mars this process could proceed using water, carbon
dioxide, and the planet's internal heat. Another possibility
is vulcanism: Although there is no evidence of currently active
Martian volcanoes, ancient methane trapped in ice "cages"
called clathrates might now be released.
The
team found methane in the atmosphere of Mars by carefully
observing the planet over several Mars years (and all Martian
seasons) using spectrometers attached to telescopes at NASA's
Infrared Telescope Facility, run by the University of Hawaii,
and the W. M. Keck telescope, both at Mauna Kea, Hawaii.
"We
observed and mapped multiple plumes of methane on Mars, one
of which released about 19,000 metric tons of methane,"
says Geronimo Villanueva of the Catholic University of America
in Washington, D.C. Villanueva is stationed at NASA Goddard
and is co-author of the paper. "The plumes were emitted
during the warmer seasons -- spring and summer -- perhaps
because the permafrost blocking cracks and fissures vaporized,
allowing methane to seep into the Martian air. Curiously,
some plumes had water vapor while others did not," he
says.
Above:
Methane plumes found in Mars' atmosphere during the northern
summer season. Credit: Trent Schindler/NASA [animation]
According
to the team, the plumes were seen over areas that show evidence
of ancient ground ice or flowing water. For example, plumes
appeared over northern hemisphere regions such as east of
Arabia Terra, the Nili Fossae region, and the south-east quadrant
of Syrtis Major, an ancient volcano 1,200 kilometers (about
745 miles) across.
It
will take future missions, like NASA's Mars Science Laboratory,
to discover the origin of the Martian methane. One way to
tell if life is the source of the gas is by measuring isotope
ratios. Isotopes are heavier versions of an element; for example,
deuterium is a heavier version of hydrogen. In molecules that
contain hydrogen, like water and methane, the rare deuterium
occasionally replaces a hydrogen atom. Since life prefers
to use the lighter isotopes, if the methane has less deuterium
than the water released with it on Mars, it's a sign that
life is producing the methane.
Whatever
future research reveals--biology or geology--one thing is
already clear: Mars is not so dead, after all.
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Editor: Dr. Tony
Phillips | Credit: Science@NASA
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