NASA's Hubble Space Telescope has detected, for the first time ever, the presence of oxygen and carbon in the atmosphere of a planet outside our solar system.

The oxygen naturally exists and is not produced by any sort of life on the gaseous hot world, astronomers caution. Nevertheless, it is a promising demonstration that the chemical composition of atmospheres on planets many light-years away can be measured. This could someday lead to finding the atmospheric biomarkers of life on extrasolar planets.

The oxygen and carbon are bleeding off the gas-giant extrasolar planet HD 209458b, orbiting a star lying 150 light-years from Earth. HD 209458b is only 4.3 million miles from its Sun-like star, completing an orbit in less than 4 days. It belongs to a class of planets called "hot Jupiters." Astronomers previously discovered that the upper atmosphere is so hot it boils hydrogen off into space.

Astronomers used the Hubble Space Telescope Imaging Spectrograph to discover a rugby-ball shaped evaporating envelope of oxygen and carbon. Analysis of the starlight passing through the envelope shows it is being ripped off by the extreme "hydrodynamic drag" created by its evaporating hydrogen atmosphere.

The planet has been dubbed "Osiris" after the Egyptian god that lost part of his body — like HD 209458b — after having been killed and cut into pieces by his brother to prevent his return to life.

The planet HD 209458b is the first transiting planet discovered, the first extrasolar planet known to have an atmosphere, the first extrasolar planet observed to have an evaporating hydrogen atmosphere, and now the first extrasolar planet found to have an atmosphere containing oxygen and carbon.