Could the detection of methane on Mars be an indication of microbial life, or is a geologic process causing this chemical anomaly?    Prior to 2003, no methane was observed in the Martian atmosphere, beginning on 2003 methane was detected using three ground-based infrared spectrometers.  This Methane was then observed over a three year period (seven Earth years).  The largest plumes were observed during the summer months, the largest contained approximately 19000 metric tons of methane.

The Martian atmosphere is composed of 95% carbon dioxide, 2.7% nitrogen, .07% carbon monoxide, .13% oxygen, 1.6% argon, and trace amounts of water vapor.   Small amounts of methane may be produced due to atmospheric processes but would be relatively short lived due to the ionization of the compound, caused by UV radiation.  Therefore any large amounts of methane present in the atmosphere would have to be the result of the release of a subsurface reservoir.  The origin of such methane reservoirs is unknown, but could be due to biologic or natural processes. 

If 90% of Earth’s methane is produced by life forms, could the methane on Mars also be produced biologically?  Extremophiles could live deep below the surface of Mars where they could use hydrogen as an energy source; this energy could be produced when water exposed to radiation is dissociated into H₂ and oxygen.  This reaction also reduces carbon dioxide to methane, which could accumulate in subsurface reservoir s.  If these reservoirs are connected to the surface along faults or fractures, seasonal variations could result in the opening of such cracks which could lead to the release of any methane accumulations.  Extremophiles of this type can be found 3 km below the Witwatersrand Basin of South Africa. 

Another possible source of the methane deposits could be of geologic origin.  Such processes could include the production of magma, or the serpentinization of basalt.  Either of these possibilities could also result in the buildup of subsurface methane deposits.  Much like the extremophile scenario, these deposits could also be released due to the temperature variations that occur with seasonal changes.

The methane appears in highest concentrations at three regions:  Arabia Terra, Nili Fossae, and the South-East corner of Syrtis Major.  The Mars Reconnaissance Orbiter and Mars Express observed that the outcrops in the Nili Fossae region are rich in hydrated minerals.  This suggests that this area resides above a magma chamber.  The largest plume was observed over shield volcano located between Sytris Major and Nili Fossae.  This further suggests that the area is above a magma chamber, and that the production of magma, or the serpentinization of basalt is responsible for the release of the methane plumes, and are probably not the result of the presents of Martian extremophiles.        

For the first time carbon dioxide has been found in the atmosphere of a planet outside of our own solar system. This is an important discovery because carbon dioxide is one the chemicals we would expect to find on a planet that harbors life, the other chemicals include: oxygen, water, and methane. Water vapor, along with carbon monoxide has previously been detected in the planet’s atmosphere.

Unfortunately, the discovery of carbon dioxide on this planet cannot be correlated to life. This Jupiter sized planet, which is located 63 light years from Earth, is known as HD 189733b. It has an orbital period of about 2.2 days and has a scorching surface temperature of about 1117 K. The close proximity of the planet to its host star may be responsible for the formation of carbon dioxide in the planet’s atmosphere. As the planet orbits, relatively close to its sun, it receives a high dosage of ultraviolet radiation. This radiation may have stripped apart other chemicals in the planet’s atmosphere while creating new chemicals, such as carbon dioxide.

The carbon dioxide was detected by analyzing the infrared spectrum of the planet. Because HD 189733b lies so close to its host star, the combined spectrum of the star/planet system had to first be analyzed and recorded. Scientists then waited for the planet to disappear behind its host star, so that the suns individual spectrum could be recorded. To obtain the planets individual spectrum, the spectrum of the star was subtracted from the star/planet system.

French astronomers discovered HD 189733b, in the constellation Vulpecula, on Oct. 5, 2005 by observing the transit of the planet across its host star. Since its discovery, the planet has reached a number of milestones. It was the first extrasolar planet to be mapped, it was the first found to contain water vapor and methane (which probably react in the high temperatures to form the carbon monoxide), and now it is the first exosolar planet known to contain carbon dioxide.

This discovery confirms our ability to detect the chemical compositions of planets outside of our solar system. If, and hopefully when, an Earth-like is discovered, analyzing the spectral signatures will be more difficult due to the small sizes of terrestrial planets. As we continue to develop our techniques by recording the spectral signatures of Jupiter-like planets, and super Earths, there should be little doubt that we will be ready to analyze the atmosphere of an Earth or Mars sized planet when the discovery occurs, bringing us one step closer to eventually detecting life on another planet.