Black Knight is an impossibly black exoplanet, a planet closer to its star than Mercury is to ours and blacker than coal. Today, it passes in front of its sun, and you can watch the transit with astronomers using the world’s largest infrared telescope.

Astronomers are commenting on the exoplanet transit as the observations from the 1.52 meter infrared Carlos Sánchez Telescope is broadcast for your viewing pleasure. The live feed will start at 5pm PDT, with the transit beginning at 5:28pm, completing its transit in exactly 1 hour and 30 minutes. [Update: The transit occurred on Saturday, but you can watch the replay!] Watch it all here:

The scientists are Slooh community observatory host Eric Edelman and astronomer Bob Berman and SETI’s Dr. Lisa Kaltenegger and Dr. Seth Shostak. You can submit questions to them on Twitter with the hashtag #DarkKnightTransits.


While any exoplanet transit is pretty cool by its very existence, TrES-2b steps it up a notch by being beyond ridiculously dark. When we first encountered this bizarre essence of darkness in planet-form, Astronomer Royal Sir Nigel Tufnel described it: “It’s like, how much more black could this be? And the answer is none. None more black.”

The atmosphere of this odd, not-so-little world is a major factor in what makes it so uniquely black. Unlike Jupiter and its light-reflecting ammonia clouds, TrES-2b has an atmosphere of vapourized sodium, potassium, and titanium oxide, chemicals that not only utterly fail to reflect light, but actively absorb it. And yet even that isn’t enough to explain how it has an albedo so low it reflects less than 1% of all light that hits it. Whatever else is going on, the end result is a planet substantially darker than any substance found on Earth.


TrES-2b is 750 lightyears away orbiting GSC 03549-02811 binary star system. Image credit: NASA/Ames/JPL-Caltech

And yet, just to screw with us trying to label it cleanly, TrES-2b is not completely dark! At just under 5 million kilometers from its star (that’s 1/10th the Mercury-Sun distance!), the planet is a scorching 1,000°C and glows faintly red like a smouldering ember. At twice the mass of Jupiter and whipping around its sun ever 2.5 days, TrES-2b is the most extreme example of a “hot Jupiter” exoplanet we’ve found.

Despite being so dark it absorbs light, TrES-2b is so hot it glows like an electric stove. Image credit: NASA/JPL-Caltech/T. Pyle

Top image: Artist’s concept of TrES-2b transiting its star, with speculative moons. Credit: David A. Aguilar (CfA)

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