Superstorm rages on an alien world

Astronomers have for the first time watched a violent superstorm on an alien world with winds blowing at up to 10,000 km (6,000 miles) per hour. High-precision obervations with a giant European telescope in Chile revealed that carbon monoxide is streaming at supersonic speeds from the day side to the night side of the planet. 
Impression of the planet in transit (ESO)

With the new data, the international team was also able to find an accurate speed for the planet’s orbit around its parent star. This in turn allowed them to “weigh” the world by measuring its mass.

They were even able to tell how much carbon there is in the planet’s atmosphere – it appears to be at a similar level to that in our own giant planets Jupiter and Saturn.

The planet, labelled HD209458b, lies around 150 light-years away in the constellation of Pegasus, the winged horse, and is about 60 per cent the size of Jupiter. Attempts have been made to weigh such planets before.

Its parent star resembles our own sun, which it zips around in just three and a half days. During this orbit it passes in front of the star, as viewed from Earth – an event called a transit. Most discoveries have been so-called “hot Jupiters” with Earthlike planet finds still rare.

The planet is 20 times closer to its home star than the Earth is to the sun. This roasts the side facing the star with temperatures reaching 1,000 C. Astronomer Simon Albrecht said: “On Earth, big temperature differences inevitably lead to fierce winds, and as our new measurements reveal, the situation is no different on HD209458b.”

Team leader Ignas Snellen said: “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 10,000 km per hour.”

He said the measurement of carbon suggested the planet formed in the same way as Jupiter and Saturn, and added: “In the future, astronomers may be able to use this type of observation to study the atmospheres of Earth-like planets, to determine whether life also exists elsewhere in the Universe.”

It may seem amazing that scientists can tell so much about a distant speck orbiting a point of starlight. They are able to do so by examining the starlight as it shone through the planet’s atmosphere during a transit, revealing the “fingerprints” of its chemistry.

The team, from the Leiden University, the Netherlands Institute for Space Research and the Massachusetts Institute of Technology in the United States, used the European Southern Observatory’s Very Large Telescope and its powerful CRIRES spectrograph to detect and analyse these faint fingerprints.

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