For those of you who don’t like the same people (or things) to always be first, there is good news. If there were to be an annual competition for which is the darkest planet out there, we would have a new winner.
Astronomers have found that a planet, which was discovered way back in 2006, is the darkest planet ever seen by the human eye (Well, technically, we didn’t see it with our own eyes. But we know of it and that’s all that matters).
The planet, unimaginatively called TrES-2b, lies at a distance of 750 light years in the direction of the constellation Draco (How many constellations are named after you, Harry Potter?). It circles the star GSC 03549-02811 (No, that’s neither a registration number, nor an account number, nor a telephone number, nor anything else that you might think it to be, except a name. Yes, that’s true).
The planet is so dark that it reflects less than 1% of the light it receives from its star. To put things into perspective, it’s blacker than coal, and even blacker than black acrylic paint. However, it’s not completely pitch black. The planet orbits its star at a distance of just 3 million miles. As a result, it gets so hot (1800° F or 980° C) that it emits a faint red glow, much like a burning ember or the coils on an electric stove. Black and hot – you would be excused if you thought we were talking about Halle Berry or Beyoncé Knowles.
Anyways, this planet’s darkness was discovered using the Kepler spacecraft, whose primary objective is to discover exoplanets – planets outside our solar system. The spacecraft does this by precisely measuring the brightness of a distant star, and the subtle dimness of that brightness when a planet passes in front of the star.
Now, it so happens that our black beauty is tidally locked with its star. “Tidal Locking” is when a planet (or moon) always presents the same side to its parent star (or planet, respectively). Such is the case with our moon as well. And so, unsurprisingly (if you managed to keep up), the planet shows changing phases as it orbits its star. Due to its changing phases, there were slight variations in the total brightness of the sun plus the planet, as the planet passed in front of its sun. Astronomers measured these variations, and after careful observations and analysis, they found that what they were viewing was the smallest ever change in the brightness of a star caused by an exoplanet. These extremely small fluctuations proved that the planet is extremely dark – in fact, the darkest because the fluctuations were the smallest. A more reflective planet would show larger brightness variations as its phase changed as it orbited around its star.
The darkness of the planet can be attributed, to some extent, to its peculiar atmosphere. Due to its very high temperature, this Jupiter-sized gas giant lacks reflective clouds. As a result, it does not reflect back the star’s light – unlike Jupiter, where huge, red-and-white storm clouds do this job pretty well. Moreover, the planet’s atmosphere consists of light absorbing chemicals like vaporised sodium and potassium, or gaseous titanium oxide. Yet none of these chemicals fully explain the extreme blackness of TrES-2b.
Official press release