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Methane on Mars causes controversy
16:26 21 September 04
NewScientist.com news service
Methane and water vapour are concentrated in the
same regions of the Martian atmosphere, say
scientists studying data from Europe's Mars
Express orbiter. They say the link may point to a
common source - possibly life - but others remain
sceptical about the detection.
In March, scientists using the Planetary Fourier
Spectrometer (PFS) on Mars Express announced they
had found methane in the atmosphere at a level of
just 10.5 parts per billion. Two other groups say
they have also detected the gas with telescopes
in Chile and Hawaii.
Ultraviolet sunlight takes about 300 years to
destroy atmospheric methane. These detections
suggest the gas is being replenished on Mars in
the same way it is on Earth - by processes such
as geothermal heating or by life forms, such as
bacteria.
Now, the PFS has found that the methane overlaps
with water vapour - long observed in the Martian
atmosphere - over three broad equatorial regions,
according to the European Space Agency (ESA).
Odyssey on ice
At low atmospheric altitudes, water vapour over
Arabia Terra, Elysium Planum, and
Arcadia-Memnonia appears two to three times� more
concentrated than at higher altitudes - 10 to 15
kilometres - where the molecule is evenly
distributed.
The team says the methane-water vapour regions
coincide with swathes of land that NASA's Mars
Odyssey spacecraft, now orbiting the planet,
suggests might contain ice.
The results were presented on Monday by PFS
principal investigator Vittorio Formisano at a
conference in Ischia, Italy.
ESA says further studies could find out if
geothermal heat is acting on an underground "ice
table" - if one exists - bringing methane and
water vapour into the air. Or perhaps
methane-producing bacteria may exist, living in
water below the posited ice table.
But Bruce Jakosky, an expert on the Martian
atmosphere at the University of Colorado in
Boulder, US, says these scenarios rely on too
many "ifs�.
"I think there are more questions than there are
answers and it's premature to speculate about
sources of methane and water or how they might be
released," he told New Scientist.
He says only one of the three groups claiming to
have detected methane has publicly written up its
results - a paper co-authored by Vladimir
Krasnopolsky of Catholic University of America in
Washington, DC, will be published in a future
issue of the journal Icarus. But even that
research raises some questions about whether
methane truly exists on Mars, says Jakosky.
Hydrogen atoms
And the evidence for a subsurface ice table
around the Martian equator is "very
controversial", he adds. It comes from Odyssey's
detection of hydrogen atoms in the top metre of
soil, which some scientists interpret as being
locked in ice and others say could come from
minerals affected by water in the past.
Furthermore, he says winds should spread water
vapour through the atmosphere too quickly for it
to be concentrated in certain spots. "It would
take a tremendous source of water in the surface
to pump water into the atmosphere faster than it
would be redistributed," he says.
Krasnopolsky, standing by his methane detection,
says winds should spread the trace amounts of
methane around too. He believes the methane he
detected is produced by bacteria that live in
"oases" where liquid water can exist - however
briefly - on the Martian surface, due to heating
by sunlight or by a hydrothermal source.
He argues that a non-biological source of methane
is unlikely because crater-counting methods
suggest no surface lava on Mars is younger than
10 million years old.
But he will not rule out the possibility that
underground bubbles of methane from ancient
volcanism might somehow be brought to the surface
to replenish the atmosphere.
Maggie McKee
http://www.newscientist.com/news/news.jsp?id=ns99996425
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