Our old friend HD 189733b is in the news again this week. As a Jupiter-sized gaseous planet orbiting a yellow dwarf in the constellation of Vulpecula, HD 189733b has become one of the best studied exoplanets.
The reason is that it’s relatively big and close to its sun, which shines through the atmosphere as the planet transits.
This phenomenon has allowed astronomers to measure many properties of HD 189733b’s atmosphere. For example, they have found that this ball of gas is rich in water and methane and that to our eyes the planet would appear a rich dark blue, a bit like Uranus.
Last year, the Spitzer Space Telescope produced a heat map of the planet showing global temperature differences. Unsurprisingly, HD 189733b is warmer at the equator than at the poles.
Astronomers also think the atmosphere is filled with particles of the condensates of iron, silicates and aluminium oxide. And today, Sujan Sengupta from the Indian Institute of Astrophysics in Bangalore, India, adds another nugget of information. It seems that these particles must be distributed in a thin layer of cloud in the upper atmosphere.
So if you’re wondering what the weather is like on HD 189733b, the answer is cloudy.
What’s emerging is the most amazing picture of a planet orbiting another sun, something that only a few years ago would have been deemed impossible.
To put this in perspective, our understanding and knowledge of HD 189733b is comparable to, and in some ways better than, our pre-Voyager knowledge of Neptune and Uranus in the 1970s.
That’s truly astounding. There can’t be many more persuasive examples of the fact that we’re currently living through a golden age of astronomy.
Ref: arxiv.org/abs/0807.1794: Cloudy Atmosphere of the Extra-solar Planet HD189733b : A Possible Explanation of the Detected B-band Polarization