The detections of methane in the martian atmosphere have challenged scientists to find a source for the gas, which is usually associated with life on Earth. One source that can be ruled out is ancient history: Methane can survive only 600 years in the martian atmosphere before sunlight will destroy it. If the global concentration of methane on Mars is 10 ppb, then an average of 4 grams of methane is being destroyed every second by sunlight. That means about 126 metric tons of methane must be produced each year to ensure a steady concentration of 10 ppb.There is an outside chance that the methane is being delivered to Mars by comets, asteroids, or other debris from space. Calculations show that micrometeorites are likely to deliver only 1 kilogram of methane a year -- far short of the 126-ton replacement level.

Comets could deliver a huge slug of methane, but the interval between major comet impacts averages 62 million years, so it's unlikely that any comet delivered methane within the past 600 years. If we can rule out methane delivery, then the methane must be manufactured on Mars. But is the source biology, or processes unassociated with life? A small percentage of Earth's methane is made through non-biological ("abiogenic") interactions between carbon dioxide, hot water and certain rocks. Could this be occurring on Mars? Perhaps, says James Lyons of the Institute for Geophysics and Planetary Physics at UCLA.

View: Full Article | Source: Astrobiology Magazine