Exoplanet
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Scientists have found what is considered the darkest planet so far discovered - a body the size of the biggest planet in our solar system, which emits only a "faint red glow," despite orbiting extremely close to its sun. According to data gathered so far, the planet, first discovered about five years ago, is darker than coal or black acrylic paint.

And scientists have yet to figure out how a planet could reflect so little light.

The planet, labeled TrES-2b and located nearly 718 light years from Earth in the direction of the constellation Draco, has been determined to reflect far less light than any known planet. Astronomers revealed their findings in a paper accepted for the Monthly Notices of the Royal Astronomical Society.

Using data from NASA's Kepler Mission, the scientists - David Kipping of the Harvard-Smithsonian Center for Astrophysics and David Spiegel from Princeton University - found that the Jupiter-sized body has a geometric albedo (a measure of reflectivity) below 1 percent.

TrES-2b belongs to a class of planets called "Hot Jupiters," meaning that they are approximately the size of the planet Jupiter, but are much hotter, owing to close proximity to their parent stars. TrES-2b has an orbit measuring 5 million kilometers, while Jupiter's orbit is 780 million kilometers. Further, the planet is "tidally locked" to its star - only one side of the planet faces the star - and thus exhibits changing phases similar to the Earth's moon.

First discovered by the Trans-Atlantic Exoplanet Survey in 2006, TrES-2b's presence was also confirmed by Hawaii-based Keck Observatory. However, it was the Kepler Mission, launched in 2009, that brought TrES-2b into focus.

The photometer on Kepler measured the brightness of the planet as it orbited, and transited its star, finding the least variation thus far recorded for any planet. A more reflective planet would have exhibited greater variation in brightness, especially given the changes in phase during its orbit.

The scientists also observed that some of the brightness had an "emission component" meaning that not all the "daylight" on the planet is reflected light, which means the actual reflectivity, or true albedo, is even lower than measured.

It is as yet unclear why. It is speculated that due to the extremely-high temperatures, the planet's atmosphere may contain light-absorbing chemicals but even these do not completely account for the very low reflectivity. The scientists concluded that "some extra opacity source" alone can explain the unusually dark nature of TrES-2b, that is, some planetary characteristic that absorbed most of the light falling on the planet.