Oxygen and carbon detected in alien atmosphere

Astronomers identify key elements around extrasolar planet.

For the first time, a team of European astronomers has detected oxygen and carbon in the atmosphere of an extrasolar planet.

What really surprised the astronomers, however, is that the carbon and oxygen are literally being blown off the planet to surround it in an extended ellipsoidal envelope, roughly the shape of a rugby ball.

Using the imaging spectrograph on the Hubble Space Telescope, the team of European astronomers, led by Alfred Vidal-Madjar of the Institut d’Astrophysique de Paris, France, studied the starlight that had passed through the atmosphere of planet HD 209458b. This Jupiter-like planet orbits very close to a star lying 150 light years away from Earth; it was the first planet to be detected by measuring the slight decrease in light as it passed in front of its star.

In 2001, astronomers uncovered evidence that the planet had an atmosphere, when they identified sodium in the spectra of light reflected from the planet.

In 2003, European astronomers discovered that hydrogen from the planet’s atmosphere was evaporating into space. It is this outflow of hydrogen, which is thought to be caused by the tremendous heat coming from the parent star, that is probably sweeping oxygen and carbon from the planet’s lower atmosphere into space.

Oxygen is a good indicator for the presence of life, but Vidal-Madjar cautions not to read too much into its detection. ’It is not a big surprise because oxygen is also present in the giant planets of our solar system, like Jupiter and Saturn,’ he says.

The research team speculates that heavier elements, such as iron, may also be actively blown off the planet.

Jon Evans