December 31, 2004
Top Space Stories of 2004: Martian Methane
Counting down the top ten astrobiology stories for 2004 highlights the accomplishments of those exploring Mars, Saturn, comets, and planets beyond Pluto. Number seven in this countdown was the startling detection of methane on Mars. Since methane concentrations would fall dramatically after only 300 years, some source of replenishing this gas is needed, whether biological or non-biological in origin.
Astrobiology Magazine -- 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.
"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.
- 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]
- 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
- 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
- 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
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