While methane in abundance can indicate life, most planets in our solar system contain some traces of methane formed by abiotic (non-life) processes. However, methane detection in an extrasolar planet suggests the chemical composition of extrasolar planets may be similar to those on earth, raising the prospects of finding life outside our solar system.
Life is unlikely to exist on the Jupiter-like planet HD 189733b because it orbits extremely close to its star resulting in immensely high surface temperatures.
Astronomers used the Hubble Space Telescope to detect the chemical signature of methane and also to confirm the existence of water vapor in the planet's atmosphere.
Photo Credit: NASA - ESA - G. Bacon