The planet is HD 189733b, one of the closest exoplanets that can be seen crossing the face of its star.
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,” research team member Frederic Pont of the University of Exeter in South West England, said.
“This means that the object that disappeared was blue,” he said.
Earlier observations have reported evidence for scattering of blue light on the planet. The latest Hubble observation confirms the evidence.
If seen directly, this planet would look like a deep blue dot, reminiscent of Earth’s color as seen from space. That is where the comparison ends.
On this turbulent alien world, the daytime temperature is nearly 2,000 degrees Fahrenheit, and it possibly rains glass — sideways — in howling, 4,500-mph winds.
The cobalt blue color comes not from the reflection of a tropical ocean as it does on Earth, but rather a hazy, blow-torched atmosphere containing high clouds laced with silicate particles.
Silicates condensing in the heat could form very small drops of glass that scatter blue light more than red light.
Hubble and other observatories have made intensive studies of HD 189733b and found its atmosphere to be changeable and exotic.
HD 189733b is among a bizarre class of planets called hot Jupiters, which orbit precariously close to their parent stars.
The observations yield new insights into the chemical composition and cloud structure of the entire class.