An Organic Molecule Worth Detecting

Organic molecules are the key ingredients for life. They are what scientists call life’s “building blocks.” So, it’s a big deal when astronomers detect such things in interstellar space. Even more so when they find them in places where life might form — like on extrasolar planets.

Astronomers using the Hubble Space Telescope have made the first detection ever of molecules of the gas methane in the atmosphere of a planet orbiting another star. As you can imagine, this is a huge breakthrough because identifying signs of life on other planets depends on finding evidence of such organic molecules. Under the right circumstances methane can play a key role in the chemical reactions that have to occur in the life-creation chain.

Methane has been detected on most of the planets, and many moons and comets in our Solar System in both gas and ice form. However, this is the first time any organic molecule like methane has been detected on a world orbiting another star. It was found in the atmosphere of a Jupiter-sized planet called HD 189733b by scientists using HST’s Near-infrared Camera and Multi-object Spectrograph (NICMOS) to break down the light from a more-distant star as it passed through the planet’s atmosphere. The planet happened to pass in front of the star, and as the star’s light traveled through the atmosphere, some of it was absorbed by gases, including methane and water vapor. That left a unique fingerprint in the spectral data, telling the astronomers that those gases exist at the planet.

Methane is composed of carbon and hydrogen. On Earth, methane is a naturally occurring product, and is also produced by a processes and life forms as varied a cattle, termines, the decay of matter in ocean and wetland environments, waste landfills and as a by-product of energy generation. It’s pretty unlikely that the methane on the distant planet around HD 189733b is generated by life, since the planet’s atmosphere is much too hot. Chances are HST noted higher methane levels on the night side of the planet, where the gas can exist in greater amounts. On the day side, the higher heat would tear apart the molecules, resulting in a lower amount of methane.

These measurements are a big step toward understanding other atmospheric conditions at this planet, or others where organic molecules will be found with HST, Spitzer, and the future James Webb Telescope.