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Jul 12, 2013 10:10 AM by Stephen Bowers

For the first time, we know the color of an exoplanet

An exoplanet is one outside our own solar system, and for the first time astronomers have determined the color of an exoplanet.

Planet HD 189733b is now known to be blue. The planet orbits a star about 63 light-years from Earth, meaning light from the star takes 63 years to reach Earth. NASA says the blue color was confirmed by observations from Hubble Space Telescope. Hubble's Image Spectrograph was used to measure changes in the color of light from the planet. Astronomers noticed that when the planet hid behind its star, there was a noticeable decrease in the amount of blue from the planet. Red light, on the other hand, did not change, and blue showed an increase when the planet came out from behind its star.

The color would be similar to Earth's blue, but not because of oceans. NASA researchers suspect the planet may be covered with clouds high in the atmosphere that contain silicate particles. The heat on the planet is so intense that it likely rains small bits of glass, which scatter blue light. 

The planet is in a class of planets called "hot Jupiters," which often orbit close to their own stars. Like Jupiter, this planet is probably a gas giant.

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