Methane in Martian Air Suggests Life Beneath the Surface
November 23, 2004
By KENNETH CHANG
A third team of scientists has now reported a seemingly
simple discovery on Mars: its atmosphere contains methane.
But that finding has potentially profound implications,
including the possibility of present-day microbes living on
Speaking this month at the American Astronomical Society's
Division for Planetary Sciences meeting in Louisville, Ky.,
Dr. Michael Mumma, a senior scientist at NASA's Goddard
Space Flight Center in Greenbelt, Md., reported three years
of observations had provided strong evidence for methane.
"We are 99 percent confident," Dr. Mumma said. "It
surprised all of us, actually. We really are still
scrambling to understand what it means."
Methane, the simplest of hydrocarbon molecules with one
carbon and four hydrogen atoms, is fragile in air and
easily broken apart when hit by ultraviolet light.
Calculations indicate that any methane in the Martian air
must have been put there within the past 300 years.
That then raises the question: What is putting methane into
the Martian air?
There seem to be only two plausible explanations. One is
geothermal chemical reactions involving water and heat like
those that occur on Earth in the hot springs of Yellowstone
or at hydrothermal vents on the bottoms of oceans.
That would intrigue planetary geologists. Although frozen
water is known to exist, there are no signs that any
volcanism has occurred there for millions of years. Also,
an instrument aboard NASA's Mars Odyssey looked for warm
spots on Mars' surface and did not find any.
The other, more intriguing, is life. On Earth, a class of
bacteria known as methanogens breathes out methane as a
waste product. The discovery, if confirmed, suggests that
perhaps Martian life arose on a presumably more hospitable
Mars billions of years ago and survives to this day
underground, beneath the cold, dry landscape.
Dr. Vladimir Krasnopolsky of Catholic University in
Washington, the leader of one of the teams, said he
believed bacteria to be the "most plausible source."
Others are more cautious. "Three difficult detections, or
marginal detections, don't equate to one really strong
one," said Dr. Philip R. Christensen, a professor of
geological sciences at Arizona State University.
Dr. Krasnopolsky's findings, relying on observations from
the Canada-France-Hawaii Telescope in Hawaii, were first
reported at a conference in Europe this year and will be
published in the journal Icarus.
In January, scientists working on the European Space
Agency's Mars Express mission also reported the detection
of the methane. A few months later, that group, led by Dr.
Vittorio Formisano of the Institute of Physics and
Interplanetary Science in Rome reported that the methane
appeared to be more plentiful in regions where frozen water
is known to exist underground.
All three teams of astronomers looked for methane molecules
in the Martian air by examining the rainbow of light
reflected by the planet. Different molecules absorb
different, very specific colors, producing a bar-code-like
series of black lines blotting out part of the rainbow
spectrum. The widths of the lines tell the quantity. Dr.
Krasnopolsky and Dr. Formisano based their claims on a
single dark line.
The journal Science published the Mars Express results this
month. Dr. Christensen of Arizona State said he was
unconvinced by it. "I must confess I'm surprised it was
published," he said. "I think it's just instrument noise.
This detection is right at the noise level of the
Dr. Mumma said his ground-based observations from Hawaii
and Chile spotted two separate dark lines corresponding to
methane and performed other checks. "Mike's a really
careful guy," said Dr. Steven W. Squyres, principal
investigator for the rovers now on Mars, who attended Dr.
Mumma's talk. "It was to me, by a significant margin, the
most compelling argument that I've seen."
There is a new wrinkle in Dr. Mumma's findings: some
regions of Mars near the equator possess surprisingly high
levels of methane, up to 250 parts per billion, while areas
near the poles had 20 to 60 parts per billion. Earth air,
by comparison, contains about 1,700 parts per billion of
methane. Dr. Mumma's readings are considerably higher than
those reported by the other two groups.
Scientists have generally thought that methane, if present,
would quickly distribute evenly through the atmosphere, so
the clumps of high concentration suggest that not only are
there sources emitting methane, but perhaps some process is
also destroying methane over the poles.
The methane findings on current-day Mars come as planetary
scientists are again rethinking their ideas about long-ago
Mars. Geological carvings on the surface, from ones that
look like meandering river channels to gigantic canyons,
gave rise to the notion that Mars had been a tropical
paradise, perhaps warmed by a thick heat-trapping blanket
of carbon dioxide in its atmosphere.
But climatologists found that it was hard for their
computer models to provide that much warming, and
scientists shifted to a picture of Mars as wet, but cold.
Many of the features could have been cut by glaciers or
transitory hellish deluges when ice was melted by meteor
Mars also possesses few carbonates, the minerals in
limestone that would be expected to form in the presence of
water, but does have much olivine, a mineral that falls
apart when exposed to moisture.
This year, however, the rover Opportunity, which landed at
a site called Meridiani Planum, found minerals and salts
that indicate that that part of Mars at least had once been
soaked in water, although when and for how long remain
uncertain. Dr. Squyres also noted that while the minerals
indicate liquid water, "We see nothing that looks like wave
ripples" in the layers of sediments preserved in the rocks.
The other rover, Spirit, on the other side of Mars,
initially found only volcanic rocks that appear almost
unchanged for billions of years. It has since rolled to
nearby hills, which appear to be slightly older, where the
rocks seem to have been significantly changed by water.
The rover findings and others presented last month in
Jackson Hole, Wyo., at a conference about early Mars have
led some to think again of the planet long ago as warm and
Even Dr. James F. Kasting, a climatologist at Penn State
whose models helped convince people that Mars had not been
warm, has changed his mind. Dr. Kasting is now
investigating methane, a more potent greenhouse gas than
carbon dioxide, as a cause of warming. His initial
simulations show methane cooling the planet but he thinks
the error is in his calculations, not his hypothesis.
"I think it's our problem, not Mars' problem," he said. "I
think the evidence keeps mounting that it was warm. I think
it has to be stably warm."
The opinion is not unanimous, but the idea of early oceans
is gaining favor. Some scientists, like Dr. Stephen M.
Clifford of the Lunar and Planetary Institute in Houston,
said that four billion years ago the decay of radioactive
elements in the core of Mars would have produced enough
heat to melt ice from below, producing an ice-covered
ocean. Acidic waters could explain the lack of carbonates.
Dr. Daniel J. McCleese, chief scientist for Mars
exploration at the NASA's Jet Propulsion Laboratory, said
that during discussions someone said, "So we all believe
there were oceans on early Mars?"
Dr. McCleese said: "Nobody spoke against that. Then someone
said, 'What about a warm climate?' And then a tumultuous