Methane Detected on Distant Planet for First Time

Sara Goudarzi
for National Geographic News
March 19, 2008
Methane has been detected in the atmosphere of a planet outside our solar system, the first time that an organic molecule has been found on a distant world.

Studies of this carbon-bearing compound could shed light on the planet's formation and evolution.

The planet, known as HD 189733b, is a so-called hot Jupiter, a gas giant similar to Jupiter that orbits very close to its parent star.

The far-flung world, discovered in 2005, is 63 light-years away in the constellation Vulpecula.

In 2007 astronomers detected signs of water on HD 189733b using NASA's Spitzer Space Telescope.

Now, using the Hubble Space Telescope, scientists have confirmed the presence of water and also detected methane.

Planets outside our solar system, called exoplanets, are so far away that scientists can't obtain images clear enough to separate the planet from its star.

So to study HD 189733b, the team used an instrument aboard Hubble called a spectrometer, which breaks up light passing through a planet's atmosphere into different bands.

"The big news is that this is the first detection of an organic in an exoplanet atmosphere," said lead study author Mark Swain, a researcher at the Jet Propulsion Laboratory and the California Institute of Technology.

The study appears in this week's issue of the journal Nature.

Transiting Planet

HD 189733b is a transiting planet, meaning it periodically passes in front of its star as viewed from Earth.

Swain's team used this fortuitous orbit to study the planet's atmosphere using the star's light.

By measuring the drop in light as the planet moved in front of the star, and by seeing how the dimming changed among light of different wavelengths, the researchers were able to determine the chemical makeup of the planet's atmosphere.

The results showed signatures of methane and water vapor but not carbon monoxide, a gas that was expected to be abundant in the upper atmosphere.

The discovery of methane and water is especially interesting, because they are prebiotic molecules, which means they are capable of participating in the formation of amino acids, the building blocks of proteins produced by living cells.

Searching for Life

On Earth, the presence of methane is associated with life.

However, due to the extreme temperatures of HD 189733b, scientists know that the gas giant cannot support life as we know it.

Methane is thought to exist in the atmospheres of most gas giants. Our local gas giants—Jupiter, Saturn, Uranus, and Neptune—all show traces of methane.

(See an interactive map of the solar system.)

The method used by Swain's team could help in other future endeavors, said Adam Showman, a researcher from the University of Arizona.

Showman wrote an accompanying article on the new discovery for Nature but was not involved with the study.

"When transiting terrestrial [rocky] planets are detected in the future, this same type of method could potentially be used to infer the composition of the atmospheres of those planets," Showman said.

"Since life can alter the chemistry of an atmosphere, this would be a powerful way of searching for evidence of life."

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