Methane is an odorless, colorless gas, consisting of a simple hydrocarbon with the chemical formula CH4. This gas had been detected in many planets in the Star Trek. In the Star Trek: The Next Generation episode "The Royale", the USS Enterprise-D encountered a planet, Theta VII, whose atmosphere consisted of methane, nitrogen and liquid neon.  In the episode "Hide and Q", an accidental explosion from a methane-like gas occurred on the Sigma III colony on Quadra Sigma III. In Star Trek: Enterprise episode "Fight or Flight", the Axanar were a species who breathed a nitrogen-methane atmosphere. In the episode "Extreme Risk", the USS Voyager encountered a class 6 gas giant that had a layer of liquid hydrogen and methane ten thousand kilometers below the outer atmosphere

Because methane primarily produced by living organisms or the anaerobic decay of organic matter, methane can be a potetnially important indicator for the existance of life on other worlds. 90 per cent of the Earth's atmospheric methane, for example, is derived from lifeforms.  In 2004, the spectral signature of methane was detected in the Martian atmosphere by both Earth-based telescopes as well as by the Mars Express probe. Methane is predicted to have a relatively short half-life in the Martian atmosphere, so the gas must be actively replenished. Since one possible source, active volcanism, has thus far not been detected on Mars, this has led scientists to speculate that the source could be microbial life. It is thought that these hardy organisms - called methanogens - do not need oxygen to thrive and can survive in the harsh atmosphere of Mars, living underground without sunlight and using hydrogen from water for energy. Microbes that produced methane from hydrogen and carbon dioxide were one of the earliest forms of life on Earth. On Earth, microorganisms thrive 2 to 3 kilometers (about 1.2 to 1.9 miles) beneath the Witwatersrand basin of South Africa, where natural radioactivity splits water molecules into molecular hydrogen (H2) and oxygen. 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.
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Thetha VIIIe

The NASA Infrared Telescope Facility discovered concentrations of methane on Mars