Astronomers discover alien planet that's blacker than coal using data from NASA spacecraft

Astronomers have found a distant planet that's blacker than coal and are not sure exactly why it's so dark.

The Harvard-Smithsonian Center for Astrophysics announced this week that it discovered the darkest known exoplanet. Its measurements show the planet, a distant, Jupiter-sized gas giant known as TrES-2b, reflects less than 1 percent of the sunlight falling on it.

That makes it blacker than coal or any of the planets or moons in our solar system.

"TrES-2b is considerably less reflective than black acrylic paint, so it's truly an alien world," astronomer David Kipping, lead author of a paper on the research, stated in the press release.

Discovery News reported astronomers are not sure exactly why the planet is so dark. It is 3 million miles from its star, much closer than the 93 million miles between Earth and the sun or the 483 million miles between Jupiter and the sun.

Its atmosphere is more than 1,800 degrees Fahrenheit, which Princeton University's David Spiegel, co-author of the paper, stated makes it emit a faint red glow "much like a burning ember or the coils on an electric stove."

The heat may be hot enough that the planet can't support reflective clouds such as seen on Jupiter, where bright clouds of ammonia reflect more than a third of the sunlight reaching it.

Kipping told BBC News that chemicals such as gaseous sodium and titanium oxide could have this effect, though he does not know whether that is the answer.

"Whilst it is possible that there is a huge overabundance of these chemicals, it is probably more likely that there is some exotic chemistry going on which we have never seen before," he said to BBC News.

"It's not clear what is responsible for making this planet so extraordinarily dark," Spiegel told Discovery.

The astronomers, using data from NASA's orbiting Kepler spacecraft, studied the amount of light coming from the planet. The BBC said they studied its "night side" and its "day side," coming up with its albedo or how much light it reflects by taking the difference between the two.

Earth's albedo is about 37 percent and Jupiter's is 52 percent, while TrES-2b's is less than 1 percent of its star's light.

The Center for Astrophyics stated that the planet orbits the star GSC 03549-02811, which is about 750 light-years away towards the constellation Draco. One light-year is about 6 trillion miles.

Kepler has found more than 1,200 planetary candidates. There will be more study of data to search for any other unusually dark planets.

The research paper will be published in the Monthly Notices of the Royal Astronomical Society.