14 DAY TRIAL // Astronomers surveying the constellation Draco found an extrasolar planet orbiting the star GSC 03549-02811, some 750 light-years away. The thing that makes this exoplanet stand out from all the rest is the fact that it's the blackest (darkest) one ever discovered.
Early measurements indicate that it reflects less than 1 percent of all the light its parent star releases. This makes it blacker than coal in our frame of reference, and much darker than any planet or moon inside our own solar system.
The hot Jupiter-class object is called TrES-2b, and got its name from the Trans-Atlantic Exoplanet Survey (TrES) that discovered it, back in 2006. Recently, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) took another look at this world.
Though it rivals in size and mass with Jupiter, the object reflects far less than the 30 percent of sunlight our gas giant does. The reason for this difference is that Jupiter is largely covered with ammonia clouds, which can be rather bright.
Due to the high temperatures it's subjected to, TrES-2b's atmosphere does not contain any such clouds. Hot Jupiters, as a rule, are extremely close to their parent stars, moving in a orbit closer than Mercury's to our Sun.
In fact, the black exoplanet is believed to lie only 3 million miles from its star. For comparison, Earth is about one astronomical unit away from the Sun, or about 93 million miles (157 million kilometers).
Calculations show that the temperature around TrES-2b exceeds 1,800° Fahrenheit. Instead of ammonia clouds, its atmosphere most likely contains vaporized sodium and potassium, as well as gaseous titanium oxide.
“TrES-2b is considerably less reflective than black acrylic paint, so it's truly an alien world,” explains CfA astronomer David Kipping, who is the lead author of the new scientific paper.
Details of the work have been accepted for publication in an upcoming print issue of the esteemed journal Monthly Notices of the Royal Astronomical Society, and are already available online.
“It's not clear what is responsible for making this planet so extraordinarily dark. However, it's not completely pitch black. It's so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove,” Princeton University astronomer and paper coauthor David Spiegel adds.
In order to observe such a dim object, the team used data provided by the NASA planet-hunting Kepler Telescope, whose job is precisely to look after exoplanets in a specific portion of the night sky.
“By combining the impressive precision from Kepler with observations of over 50 orbits, we detected the smallest-ever change in brightness from an exoplanet: just 6 parts per million. In other words, Kepler was able to directly detect visible light coming from the planet itself,” Kipping concludes.