Methane is a simple organic substance commonly found in the atmosphere of many different worlds across the universe. The simplest of hydrocarbons, a molecule of methane is composed of one carbon atom linked to four hydrogen atoms. On Earth-like planets, methane is a lighter-than-air gas and its presence contributes to the greenhouse effect. Many microorganisms are able to produce methane through a form of anaerobic respiration known as methanogenesis. On cold worlds like Titan, the largest moon of Saturn, the compound is found in the liquid state, forming methane lakes and ponds.