Mysterious Martian Methane

methane photochemistry
Chemical reactions triggered by ultraviolet (hv) in the thin martian atmosphere.
Credit: Sushil, UMich

Six years ago, then NASA Associate Administrator Wesley Huntress, Jr., stated , "Wherever liquid water and chemical energy are found, there is life. There is no exception." Few opportune years like 2004 have presented astrobiology with as many remarkable vistas and fresh perspectives on this fundamental triad of water, chemical energy and life.

Consider this year’s accomplishments of those dedicated to searching for life in the universe.

Landing on Mars not once, but twice. Then finding evidence for water on opposite sides of the red planet. Picking up what appears to be methane signals in the martian atmosphere, one of the residues that might prove one day to be the product of underground biology. Scientists began to discuss seriously what colonization strategies make sense.

Setting off to explore the even richer atmosphere of the Earth-like moon, Titan. Spiraling into orbital capture around Saturn and photographing its majestic rings.

Flying through the tail of a comet and heading home after collecting the first extraterrestrial samples from such dusty iceballs. Launching the Deep Impact probe to smash into a comet and watch how the dust and ice get kicked up.

Filling the astronomy catalogs with well over a hundred new planets, including what may prove to be the first visible exoplanet. Finding some nearby candidates that might occupy temperate locations or safely orbit Sun-like stars.

Witnessing the once-per-century passage of our neighboring Venus across the face of the Sun. The MESSENGER probe took off on its decade long tour of the inner solar system to orbit Mercury.

Discovering the largest planetoids beyond Pluto among those outer nurseries where only comets visit.

The editors of Astrobiology Magazine revisit the highlights of the year and where possible point to one of the strongest lineups ever for beginning a new turn of the calendar. Between the marathon still being run by the twin Mars rovers and the expected descent to Saturn’s moon, Titan, next year promises no letdowns.

Ophir Chasm
Perspective view. Ophir Chasm in northern Marineris Valley network.
Credit: ESA/Mars Express

Number seven on the countdown of 2004 highlights was detection of methane on Mars. Relatively high levels of methane have been detected on Mars using a combination of ground based spectroscopy and the orbiting Mars Express probe.

Mars resembles Earth more than any other planet in our solar system, and studying its atmosphere gives us a greater understanding of our own.

Having methane appear on Mars is something of a mystery, because the planet was not believed to have active volcanism or tectonics. Could the methane be evidence of martian life forms buried underground?

Methane on Mars could be produced by non-biological methods or by biological ones. "Biologically produced methane is one of many possibilities," said Sushil Atreya, professor and director of the Planetary Science Laboratory in the University of Michigan College of Engineering. "Methane is a potential biomarker, if a planet has methane we begin to think of the possibility of life on the planet. On Earth, methane is almost entirely derived from biological sources."

How the methane got to Mars is the big question, and there are several possible sources, Atreya said. The most exciting scenario is that methanogens—microbes that consume the Martian hydrogen or carbon monoxide for energy and exhale methane—dwell in colonies out of sight beneath the surface of the red planet.

Ophir Chasm
Perspective view. Ophir Chasm in the northern Marineris Valley network.
Credit: ESA/Mars Express

"These are anaerobic so they don’t need oxygen to survive, if they are there," Atreya said. "If they are there, they would be underground."

Spectrocopy detected an average 10 parts per billion by volume (ppbv) of methane on Mars, a small amount compared to the approximately 1700 ppbv on Earth. The methane gas was distributed unevenly over Mars’ surface, which tends to support the theory that an internal, on-site source, rather than a comet, is the source generating the methane, said Atreya.

Speculation is tempting, but many more experiments are necessary before drawing any conclusions.

"While it’s tantalizing to think there are living things on Mars, we aren’t in a position to say that is what is causing the methane," Atreya said.

What Next?

2005
– Mars Reconnaissance Orbiter (MRO) launch, Mars Orbiter to collect high-resolution, 1-meter, images in stereo-view of Mars
– European Venus Express, Venus Orbiter for two-year nominal mapping life [486 days, two Venus year]

2006
New Horizons, Pluto and moon Charon flyby, mapping to outer solar system cometary fields and Kuiper Belt
Dawn, Asteroid Ceres and Vesta rendezvous and orbiter, including investigations of asteroid water and influence on meteors
Kepler, Extrasolar Terrestrial Planet Detection Mission, designed to look for transiting or earth-size planets that eclipse their parent stars [survey 100,000 stars]
Europa Orbiter, planned Orbiter of Jupiters ice-covered moon, Europa, uses a radar sounder to bounce radio waves through the ice
– Japanese SELENE Lunar Orbiter and Lander, to probe the origin and evolution of the moon

2007
– Japanese Planet-C Venus Orbiter, to study the Venusian atmosphere, lightning, and volcanoes.
– Mars Scout mission, final selections August 2003 from four Scouts: SCIM, ARES, MARVEL and Phoenix
– French Mars Remote Sensing Orbiter and four small Netlanders, linked by Italian communications orbiter

2009
BepiColumbo, European Mercury Orbiters and Lander, including Japanese collaborators, lander to operate for one week on surface
Mars 2009, proposed long-range rover to demonstrate hazard avoidance and accurate landing dynamics


Related Web Pages

2003: Year in Review
Solar System Exploration Survey
Stardust
Genesis
Mars Opportunity Rover
Mars Spirit Rover
Mars Express
Mars Methane
New Planets
Saturn Cassini
Venus Occultation
Planet Ten: Beyond Pluto?