5,400 mph Winds Discovered Hurtling Around Planet Outside Solar System

From University of Warwick

Winds exceeding 1.2 miles per second (2 km per second) have been discovered flowing around a planet outside of the 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 20x greater than the fastest ever known on Earth, where it would be seven times the speed of sound.

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

Studying the exoplanet HD 189733 b, the Warwick researchers measured the velocities on the two sides of HD 189733 b and found a strong wind moving at more than 5,400 mph (8,690 kph) blowing from its dayside to its night side. Louden explained: “HD 189733 b’s velocity was measured using high resolution spectroscopy of the sodium absorption featured in its atmosphere. As parts of HD 189733 b’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.”

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. Co-researcher, Dr. Peter Wheatley of the University of Warwick’s Astrophysics Group explained:

"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 189733 b is one of the most studied of a class of planets known as hot Jupiters. At over 10 percent larger than Jupiter, but 180x closer to its star, HD 189733 b has a temperature of 1200 degrees Celsius. 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 HARPS, the High Accuracy Radial velocity Planet Searcher, in La Silla, Chile.

The research, Spatially resolved eastward winds and rotation of HD 189733b, is published by Astrophysical Journal Letters.