Usually when astronomers spot a new planet, they can sometimes capture images of it using highly specialized equipment. Now, however, they’ve found a planet so dark it absorbs almost all the light hitting it.
They’ve nicknamed it a “charcoal planet”, one of the darkest planets ever discovered.
The planet, WASP-104b, is a type of planet known as a “hot Jupiter”. These are gas giants with masses similar to that of Jupiter, but with much smaller orbits. Most are close enough to complete a circuit around their star within 10 days. Because of this, they’re also obviously very hot. But while they’re not quite rare, these kinds of planets do have a strange set of similarities about them.
One of these is that these hot Jupiters are darker than other kinds of planets, reflecting only about 40 percent of the light reaching them. However, there are occasionally some of them that are a lot darker, like the WASP-12b discovered last year. That one, scientists discovered,
But occasionally, astronomers will find one that’s a lot darker – like WASP-12b, which last year was discovered to absorb at least 94 percent of the light that hits it. And yet, the new WASP-104b is even darker than that. According to researchers at Keele University in the UK, the planet absorbs more than 97 to 99 percent of light reaching it. It’s so dark it’s almost as black as a black hole.
“From all the dark planets I could find in the literature, this is top five-ish,” lead researcher and astrophysicist Teo Mocnik told New Scientist. “I think top three.” And the reason might be because it’s so close to its star.
WASP-104b orbits a yellow dwarf about 466 light-years away from us in the Leo constellation and is, like most hot Jupiters, tidally locked. That means one side of the planet is always facing the star, dividing it into a permanent day side and night side. In addition, it’s just 4.3 million kilometres away from its star, meaning it completes an orbit in just 1.75 days.
Because of this, the day side is so hot that clouds can’t form, which are what help reflect light. The same for another natural reflector, ice. Instead, WASP-104b has a thick, hazy atmosphere, likely brimming with atomic sodium and potassium, both of which which absorb visible spectrum light, making the day side look very dark. Of course, the night side doesn’t even receive any light, so there’s nothing to reflect.
In fact, the only reason we know the planet is there is because we don’t watch for the planet-shine from those far away. We instead look for the periodic dimming and brightening of light from a star, indicating there’s a planet revolving around it.
The darkest hot Jupiter we’ve seen yet is TrES-2b, which reflects as little as 0.1 percent of the light that hits it. But as scientists continue to probe, they could very well find that WASP-104b, beats it out for the title.