The extra-solar weather report was published recently in the Astrophysical Journal Letters. It's no easy thing to get a forecast for a planet 60 light years away. In fact, the University of Warwick researchers who managed it believe they're the first scientists to directly measure and map weather phenomenon on a planet outside of our solar system.
So how was it done? HD 189733b is an ideal target for study: In addition to being (relatively) close to home, it's a nice big observational target, 10 percent larger than Jupiter. It's also very close to its host star, which comes in handy because of the way we study exoplanets.
The observations made with space telescopes when a planet passes in front of its star tell us basically everything we know about exoplanets. Scientists can look at the fading and winking of a star's visible light and use those changes to model the planets that must be passing in front of it. You may recall that a distant star's unusual blinking patterns recently had some speculating that alien spacecraft might be orbiting it (but that almost certainly wasn't the case).
A star's shine can help scientists look at its planet's atmosphere, too. When the planet passes in front of its host, scientists can measure the star's light as its absorbed by molecules in the atmosphere. These wavelengths warp as the planet moves,for the same reason that a siren sounds funny as it speeds away from you. Interpreting those changes -- which are directly related to the speed at which the molecules are moving -- allowed the researchers to calculate wind speeds on the distant world.
“The surface of the star is brighter at the centre 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," lead researcher Tom Louden said in a statement. "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 hope is that researchers can use this technique to figure out wind conditions on other exoplanets -- including ones a lot more like Earth. After all, a planet with all the necessary ingredients for life still wouldn't be too hospitable if it also boasted mach 7 winds.