NASA’s Hubble Finds a True Blue Planet – annotated

ABOUT THIS IMAGE:
This illustration shows a hot-Jupiter-class planet orbiting its yellow-orange star, HD 189733. NASA's Hubble Space Telescope measured the actual visible-light color of the planet, which is deep blue. This color is not due to the presence of oceans, but is caused by the effects of a 2,000-degree-Fahrenheit atmosphere where silicate particles melt to make "raindrops" of glass that scatter blue light more than red light.

The planet HD 189733b was discovered in 2005 and is only 2.9 million miles from its parent star. The planet is so close to its star that it is gravitationally "tidally locked" so that one side always faces the star and the other side is always dark. In 2007 NASA's Spitzer Space Telescope made a thermal map that identified the presence of an early afternoon hotspot on the planet, as shown here. High-altitude clouds, laced with silicates, may blow from the day side to the night side at 4,500 miles per hour.

Because the planet is only 63 light-years from Earth, a visitor would see many of the same stars we see in our nighttime sky, though the constellation patterns would be different. Our Sun and the nearest star to our Sun, Alpha Centauri, appear as two faint stars near image center.