Watch as Dr. Michael Mumma explains what his discovery of methane on Mars means for finding other life or other extreme geological processes in the Solar System. Courtesy of NASA.
The surprising thing about finding methane on Mars is first
that astronomers detect it. The gas is not stable in the planet’s
atmosphere. It goes away rapidly which means the methane is
recently generated and continually re-generated, says Michael
Mumma of NASA’s Goddard Spaceflight Center.
He and his colleagues discovered traces of the gas using spectroscopy,
and to their surprise only detected it in certain areas, which
means it’s coming from discrete vents, Mumma explains.
Using spectroscopy instruments attached to the Keck and NASA
infrared telescopes, the scientists spread the Martian light
into its component colors or wavelengths just as a prism separates
white light into the colors of the rainbow and created a light
spectrum. Mumma and his colleagues then looked for dark areas
in specific places along the spectrum.
At these points, methane, if present in the atmosphere, would
absorb sunlight reflected from the Martian surface. The team
found three of these features called absorption lines, which
together are a definitive signature of methane.
To verify their result and ensure that they were not detecting
the Earth’s own methane, the scientists used the motion
of the Red Planet to look for a shifted position of the Martian
absorption lines. Now that methane has been detected, scientists
next want to know whether the methane is produced biologically
or geologically, or by both processes. Right now it’s
too hard to tell, but the question is intriguing, Mumma says.
This image shows the methane signature
Mumma and his colleagues detected in June 2006 using
Keck’s NIRSPEC instrument, or Near Infrared Spectrometer.
Courtesy of Michael Mumma, NASA.
Methane is the main component of the natural gas found on Earth
and is made of four atoms of hydrogen bound to a carbon atom.
Terrestrial organisms actually release 90 percent of our planet’s
methane as they digest nutrients. Other purely geological processes,
like oxidation of iron, release the other ten percent. But,
because such a large proportion of the Earth’s gas comes
from living creatures, the discovery of methane on Mars is
a tantalizing result, especially for astrobiologists.
Scientists looking for life on other planets are excited
by the results because on Earth about two to three kilometers,
or about mile and a half, beneath the Witwatersrand basin of
South Africa, terrestrial microorganisms thrive. The microorganisms use hydrogen,
which forms from natural radioactivity splitting water molecules
into molecular hydrogen and oxygen, for energy. So, if microscopic
Martian creatures are producing the methane, they too likely
live, and could very well have survived for billions of years,
below the permafrost layer on Mars.
An aquifer below the Red Planet’s permafrost layer would
hold the necessary liquid water, radioactive decay would supply
energy and carbon dioxide or carbonates could provide carbon
for Martian microorganisms to manufacture methane as a bi-product
of their metabolism. The gas and other substances, such as
ethane and hydrogen sulfide (accumulating now or previously
in such underground zones), could then seep into the atmosphere
through the planet’s pores or fissures. Warm temperatures might
cause the planet’s surface ice plugs to open seasonally
at crater walls or canyons, and the gas could then escape from
the deep zones into the atmosphere.
Methane spews from discrete regions on
the Martian surface. This image shows the intensity of
the release along three regions of the Red Planet’s
surface. All of these regions show a past history of
having ancient ground ice or flowing water. Courtesy
of Michael Mumma, NASA.
According to their observations, during mid-summer in the Martian
northern hemisphere, one vent released 19,000 metric tons of
methane, comparable to that of the massive hydrocarbon seep
at Coal Oil Point in Santa Barbara, Calif. The other observed
plumes also burped up methane during the spring in the Martian
southern hemisphere and were detected over regions that show
either evidence of ancient ground ice or the flow of liquid
water. But during the Martian winter the temperature drops,
the ice returns and the cracks that release the gas are plugged
up, so the methane signal disappears. Mumma adds that rather
than being sealed as vapor inside ice-covered rock reserves,
the methane could also be trapped inside molecular cages called
clathrates. Connecting gas-filled voids in the rock with the
atmosphere by clearing plugged pores and fissures would reduce
the gas pressure and de-stabilize clathrates, perhaps releasing
methane and water vapor.
Coupling the Laser Guide Star, seen here,
with the NIRSPEC instrument, will allow Mumma and his
colleagues to better pinpoint the geographic origins
of Martian methane. Credit: Laurie Hatch.
“Of course, we can’t state with certitude that
the methane is biologically produced, and so we also consider
geochemical mechanisms,” Mumma says.
One way to create methane geochemically is through the combination
of iron oxide, carbon dioxide and water under very high temperatures
and pressures. The process, which occurs on Earth so it might
also occur on Mars, transforms the water, gas and oxide into
minerals called serpentines. But because the process takes
place far below ground, the ensuing methane could be trapped for
long periods, later venting into the atmosphere if seasonal
warming opens pores and fissures at scarp faces.“One
of the most important consequences of our discovery is that
we’ve identified certain signposts on Mars that are basically
little flags that say ‘Come here. Here I am’,” he
says. “But the big question is whether this methane was
produced biologically or geochemically?”
Searching for other sites
To answer this question will take much follow-on research,
Mumma explains. Not only will it require landers and rovers
exploring the “little flags” but it will also require additional spectroscopic measurements. In a new initiative
with the Keck telescope, he will use the adaptive optics
system, AO, in combination with the NIRSPEC instrument to more
precisely locate, down to a resolution of 50 kilometers, the
regions that are leeching the methane.
With NIRSPEC and AO, Mumma also plans to search for other trace
gases on Mars such as ethylene, formaldehyde and ethane. Finding
them will give a better idea of whether the methane’s
origin is geological or biological, and combining this data
with information dug up by robot crafts sent to Mars will eventually
tell us whether or not we have or have had living counterparts
only a planet away.
