First exoplanet weather map reveals 5,400 mph winds

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The planet HD 189733 in front of its parent star with a belt of wind around the equator travelling at 5,400 mph (8,700 km/h)(Credit: Mark A. Garlick/University of Warwick)

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Scientists from the University of Warwick have produced the first weather map of a planet outside our solar system. The planet in question – HD 189733b – is not likely to top the list of interstellar tourist destinations. Based on ground observations, the map shows winds 20 times faster than any recorded on Earth, or seven times the speed of sound.

HD 189733b is an extrasolar planet orbiting the star HD 189733 about 63 light-years from Earth in the constellation of Vulpecula. Thirteen percent more massive than Jupiter, it orbits its parent star in 2.2 days, making it a "hot Jupiter" with a surface of temperature of 1,200º C (2,200º F) Since it's believed to be the closest such planet to us, it's of particular interest to astronomers. It's also the first extrasolar planet to be thermally mapped, as well as to have its deep blue color (perhaps due to silicate particles) determined and to have carbon dioxide detected in its atmosphere.

Earlier this year, scientists reported mapping weather patterns on the exoplanet Kepler-7b, but this were general day/night temperature variations. What the University of Warwick's Astrophysics group achieved is the first time that a weather system on a planet outside the Solar System has been directly measured and mapped using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument in La Silla, Chile. Using observational data, the Warwick group calculated that HD 189733 has winds of over 2 km/s (Mach 7, 5,400 mph) raging across its surface as the heated air on the daylight side of the planet flows to the night side

The planet HD 189733 at three positions as it crosses its parent star(Credit: Mark A. Garlick/University of Warwick)

"HD 189733b's velocity was measured using high resolution spectroscopy of the sodium absorption featured in its atmosphere," says Tom Louden, of the Warwick group. "As parts of HD 189733b's atmosphere move towards or away from the Earth the Doppler effect changes the wavelength of this feature, which allows the velocity to be measured.

"The surface of the star is brighter at the center than it is at the edge. So as the planet moves in front of the star, the relative amount of light blocked by different parts of the atmosphere changes. For the first time we've used this information to measure the velocities on opposite sides of the planet independently, which gives us our velocity map."

The Warwick group says that the technique used to calculate the winds on HD 189733 could also be used to study the weather systems on more Earth-like planets

The Warwick group's results were published in Astrophysical Journal Letters.

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