'Superstorm' rages on exoplanet

BBC News - 'Superstorm' rages on exoplanet

Data on carbon monoxide gas in the atmosphere show that it is streaming at fierce speeds from the planet's hot day side to its cool night side.

Writing in Nature, a team detected longitudinal winds of roughly 2km/s (7,000km/h) in the atmosphere of a "hot Jupiter" planet.

Hot Jupiters are gas giants that orbit very close to their parent stars.

The planet HD209458b orbits a star in the constellation Pegasus, some 150 light-years away. It circles this star at around one-eighth the distance Mercury orbits Earth.

This means the exoplanet is heated intensely by its parent star, and has a surface temperature of about 1,000C on its hot side.

But as the planet always has the same side to its star, one side is broiling, whereas the other is much cooler.

"On Earth, big temperature differences inevitably lead to fierce winds, and as our new measurements reveal, the situation is no different on HD209458b," said co-author Simon Albrecht.

Ignas Snellen, who led the team of astronomers, commented: "HD209458b is definitely not a place for the faint-hearted.

"By studying the poisonous carbon monoxide gas with great accuracy we found evidence for a 'super wind', blowing at a speed of 5,000 to 10,000km per hour."

In Nature, the authors also report a new technique for obtaining an exoplanet's mass. They directly calculated the velocity of the exoplanet as it orbited its home star - its orbital velocity.

They did this by first measuring its "Doppler shift" - the apparent change in the frequency of sound or light waves caused either by movement of the observer or by the source of the waves (in this case the planet).

Once the orbital velocity of HD209458b could be determined, the masses of both the star and planet could be calculated using Newton's law of gravity.