Hints At Microscopic Organisms, Possible Liquid Water
team of NASA and university scientists has achieved the first
definitive detection of methane in the atmosphere of Mars. This
discovery indicates the planet is either biologically or
The team found methane in the Martian atmosphere by carefully
observing the planet throughout several Mars years with NASA's
Infrared Telescope Facility and the W.M. Keck telescope, both at
Mauna Kea, HI. The team used spectrometers on the telescopes to
spread the light into its component colors, as a prism separates
white light into a rainbow. The team detected three spectral
features called absorption lines that together are a definitive
signature of methane.
"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," said Michael Mumma of NASA's Goddard
Space Flight Center in Greenbelt, MD. "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, CA."
Mumma is lead author of a paper describing this research, which
appeared in Science Express on Thursday.
Methane, four atoms of hydrogen bound to a carbon atom, is the
main component of natural gas on Earth. Astrobiologists are
interested in these data because organisms release much of Earth's
methane as they digest nutrients. However, other purely geological
processes, like oxidation of iron, also release methane.
"Right now, we do not have enough information to tell whether
biology or geology -- or both -- is producing the methane on Mars,"
Mumma said. "But it does tell us the planet is still alive, at
least in a geologic sense. It is 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 is warm enough for liquid
water to exist. Liquid water is necessary for all known forms of
life, as are energy sources and a supply of carbon.
"On Earth, microorganisms thrive about 1.2 to 1.9 miles beneath
the Witwatersrand basin of South Africa, where natural
radioactivity splits water molecules into molecular hydrogen and
oxygen," Mumma said. "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.
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."
It is possible a geologic process produced the Martian methane,
either now or eons ago. On Earth, the conversion of iron oxide 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. Although there is no evidence of active volcanism on
Mars today, ancient methane trapped in ice cages called clathrates
might be released now.
According to the team, the plumes were seen over areas that show
evidence of ancient ground ice or flowing water. Plumes appeared
over the Martian northern hemisphere regions such as east of Arabia
Terra, the Nili Fossae region, and the south-east quadrant of
Syrtis Major, an ancient volcano about 745 miles across.
One method to test whether life produced this methane is by
measuring isotope ratios. Isotopes of an element have slightly
different chemical properties, and life prefers to use the lighter
isotopes. A chemical called deuterium is a heavier version of
hydrogen. Methane and water released on Mars should show
distinctive ratios for isotopes of hydrogen and carbon if life was
responsible for methane production. It will take future missions,
like NASA's Mars Science Laboratory (illustrated above), to
discover the origin of the Martian methane.