Hubble detects methane on distant planet

March 19, 2008

NASA's Hubble Space Telescope has detected methane in the atmosphere of a planet 63 light-years away, marking the first discovery of an organic compound on a planet outside our Solar System.

The methane was found on a Jupiter-sized planet named HD 189733b. The planet closely orbits HD 189733, a yellow dwarf star in the constellation Vulpecula.

Although methane can play a key role in the chemical reactions needed to form life, the planet is too close to its parent star to support life, scientists say. It is known as a "hot Jupiter" - a planet whose mass is comparable to that of Jupiter, but orbits nearer to the parent star than Mercury, our Solar System's innermost planet.

This particular hot Jupiter takes just two days to completely orbit its parent star, and the temperatures in its atmosphere can reach 1,650 degrees Fahrenheit, around the melting point of silver.

"The methane here, although we can call it an organic constituent, is not produced by life - it is way too hot there for life," said Giovanna Tinetti, part of the NASA team that made the discovery.

However, scientists believe the spectroscopic methods used to detect the methane can be used to find organic compounds on other distant planets. "This observation is proof that spectroscopy can eventually be done on a cooler and potentially habitable Earth-sized planet orbiting a dimmer red dwarf-type star," said Mark Swain, a NASA scientist whose paper on the discovery will appear in the scientific journal Nature.

Spectroscopy is the splitting of light into its components. As the light from the star passed through the planet's atmosphere, the atmospheric gases imprinted their chemical signature onto the light, allowing the atmosphere's chemical composition to be analyzed by Near Infrared Camera and Multi-Object Spectrometer. To their surprise, astronomers found much higher levels of methane than had been predicted for hot Jupiters. "This indicates we don't really understand exoplanet atmospheres yet," said Swain.

This discovery also confirmed the presence of water molecules in the planet's atmosphere, which was found by NASA's Spitzer Space Telescope last year using spectroscopy. "With this observation there is no question whether there is water or not - water is present," Swain said.

The ultimate goal of these studies is to identify the molecules of more Earth-like planets in the habitable zone of stars, where conditions may be favorable for life.

Adam Showman at the University of Arizona said, "We are thus now seeing but the opening salvo in a revolution that will extend humankind's view of planetary worlds far beyond the provincial boundaries of our Solar System."

Giovanna Tinetti, who co-authored the Nature article, believes the concept of life on other planets is not too unlikely. "My personal view is it is way too arrogant to think that we are the only ones living in the Universe," she says.