That image is an artist's impression. Hubble doesn't have anywhere close to the resolution to resolve a planet 63 light years away. That planet is about 1/1000 of a Hubble pixel across.
Good call! How can they study something that is 1/1000 of a Hubble pixel?
Hubble's Space Telescope Imaging Spectrograph measured changes in the color of light from the planet before, during and after a pass behind its star. There was a small drop in light and a slight change in the color of the light. "We saw the light becoming less bright in the blue but not in the green or red. Light was missing in the blue but not in the red when it was hidden," said research team member Frederic Pont of the University of Exeter in South West England. "This means that the object that disappeared was blue."
The paper on this was just published in The Astrophysics Journal Letters.
Evans, T. et al., The deep blue color of HD 189733b: albedo measurements with HST/STIS at visible wavelengths, 2013 ApJ 772 L16.
Official paper: http://iopscience.iop.org/2041-8205/772/2/L16
Pre-publication version: http://www.spacetelescope.org/static/archives/releases/science_papers/heic1311.pdf.
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