Astronomers have measured and mapped a weather system on a planet outside our solar system for the first time, and I’m sad to report that interstellar camping trips maaaay not be so much fun after all. On planet HD 189733b, at least, the winds are blowing at a breathtaking 5,400 miles per hour.
That’s the latest discovery of a team of exoplanet researchers at the University of Warwick, who measured air currents on either side of HD 189733b—located 63 light years away in the Vulpecula constellation—as it passed in front of its star. From the gas giant’s dayside to its nightside, the winds are gusting at approximately seven times the speed of sound. Put another way, a day on HD 189733b is twenty times windier than the windiest day ever recorded on Earth.
How do you even begin to measure the wind on a planet that’s little more than a faint shadow crossing in front of a distant star? By taking advantage of the Doppler effect.
Remember that one from high school physics? It’s the reason an ambulance’s siren becomes higher pitched as it speeds toward you: The frequency (and in the case of sound, pitch) of a wave as perceived by an observer changes depending on the relative velocity of the object producing that wave.
Only in this case, we’re talking about lightwaves instead of sound, and the moving object in question is the planet itself.
Planet HD 189733b crossing in front of its star. The changing illumination of the planet’s atmosphere allowed astronomers to measure wind speeds. Image Credit: Louden and Wheatley 2015.
As HD 189733b’s two hemispheres alternately swung towards and away from the Earth, astronomers measured subtle shifts in the wavelengths of light scattering off its atmosphere. Specifically, the atmosphere appeared blue-shifted as it rotated toward our telescopes; red-shifted as it spun away. After correcting for the rotation of the planet itself, the astronomers used this Doppler shift to calculate windspeed and direction.
“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,” lead researcher Tom Louden said in a statement.
HD 189733b is a giant, hot blob of gas—not exactly a great vacation prospect. But in the future, Louden’s technique might be used to study the atmospheres of small, rocky planets, and to figure out how “Earth-like” they actually are.
“We are tremendously excited to have found a way to map weather systems on distant planets,” study co-author Peter Wheatley said. “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.”
Maybe we’ll find another cozy blue marble somewhere out there. But in light of interstellar forecast #1, I’m feeling pretty darn grateful to live on Earth.
[Read a pre-print of the scientific paper at arXiv]
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Top: Artist’s concept of HD189733, a “hot Jupiter” that sits very close to its parent star. Image Credit: Mark A. Garlick/University of Warwick