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Mapping winds on alien worlds

Astronomers discovered winds over 5,400 mph (8,700 km/h) flowing around exoplanet HD 189733 b.
Exoplanet HD 189733b
University of Warwick
Winds of over 1.2 miles (2 kilometers) per second have been discovered flowing around a planet outside of Earth’s solar system, new research has found.

The University of Warwick discovery is the first time that a weather system on a planet outside of Earth’s solar system has been directly measured and mapped.

The wind speed recorded is 20 times greater than the fastest known on Earth, where it would be seven times the speed of sound.

Commenting on the discovery, Tom Louden of the University of Warwick’s Astrophysics group said, “This is the first ever weather map from outside of our solar system. While we have previously known of wind on exoplanets, we have never before been able to directly measure and map a weather system.”

The Warwick researchers measured the velocities on the two sides of exoplanet HD 189733b and found a strong wind moving at over 5,400 mph (8,700 km/h), blowing from its dayside to its night side, Louden said.

“HD 189733b’s velocity was measured using high resolution spectroscopy of the sodium absorption featured in its atmosphere. As parts of HD 189733b’s atmosphere move towards or away from Earth, the Doppler effect changes the wavelength of this feature, which allows the velocity to be measured.”

Explaining how this information was used to measure velocity, Louden said: “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 researchers say that the techniques used could help the study of Earth-like planets. Peter Wheatley of the University of Warwick said: “We are tremendously excited to have found a way to map weather systems on distant planets. As we develop the technique further, we will be able to study wind flows in increasing detail and make weather maps of smaller planets. Ultimately this technique will allow us to image the weather systems on Earth-like planets.”

HD 189733b is one of the most studied of a class of planets known as “hot Jupiters.” At over 10 percent larger than Jupiter but 180 times closer to its star, HD 189733b has a temperature of 3,300° F (1,800° C). Its size and relative closeness to our solar system make it a popular target for astronomers. Past research has shown that the day side of the planet would appear a bright shade of blue to the human eye, probably due to clouds of silicate particles high in its atmosphere.

The data was collected by the High Accuracy Radial velocity Planet Searcher in La Silla, Chile.
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