Hubble finds a blue exoplanet

Astrophysicists have confirmed that at least one other exoplanet in the Milky Way galaxy is blue. You can see a somewhat melodramatic artist’s impression below.

Even through the Hubble telescope, exoplanets are usually too close to their stars to directly observe, and HD 189733b is no exception. Light reflected from the planet blends with light coming from its star. However, Tom Evans at the University of Oxford and his colleagues used an ingenious method to separate out the contribution of light from the planet. They compared spectrographic data of the star plus planet to data from just the star when the planet was eclipsed behind it. When the planet was behind the star, there was less blue light, indicating that the planet was the source of that blue light.

Although this is exciting news, we shouldn’t plan waterskiing trips to HD 189733b. There’s every indication that the planet is a gas giant, similar to Jupiter. It most likely does not contain liquid water or even a water vapor atmosphere. Researchers speculate that the blue color could be due to a low lying clouds of silica (glass).

The folks at Space.com have created the following helpful infographic:






Thomas M. Evans, Frédéric Pont, David K. Sing, Suzanne Aigrain, Joanna K. Barstow, Jean-Michel Désert, Neale Gibson, Kevin Heng, Heather A. Knutson, & Alain Lecavelier des Etangs (2013). The Deep Blue Color of HD 189733b: Albedo Measurements with Hubble Space Telescope/Space Telescope Imaging Spectrograph at Visible Wavelengths The Astrophysical Journal Letters, 772 (2) : doi:10.1088/2041-8205/772/2/L16.