Super-heated exoplanet is dark due to its atmosphere’s energy absorption
There is a dark object closely orbiting the star WASP-12A, circling it close to every 24 hours. This object reflects almost no light, making it as dull and black as new asphalt, and thus rather difficult to see in the visible spectrum. It’s not dark matter, nor is it a black hole in the making. Instead, it’s simply an extremely overcooked planet. Rather than reflecting light off its atmosphere into space so we can see it, the hydrogen and helium miasma that surrounds planet WASP-12B absorbs nearly every bit of energy its star throw at it, further fueling its extreme temperatures and eventual destruction.
WASP-12B is what’s known as a “hot Jupiter,” because it’s two-times larger than our solar system’s premier gas giant, while also holding above average temperatures in its atmosphere. However, that title really doesn’t capture the nature of WASP-12B’s atmosphere, which is 4,600° Fahrenheit one side, and around 2,600° Fahrenheit on the other. The large disparity is because the planet is tidally locked, meaning the “day” side of the planet is always facing its star, while the “night” side always dark. This arrangement means that temperatures have a harder time equalizing, since winds flowing from one side to the other can only do so much to mitigate the effects of constant heat exposure. At this point, the molecules in the atmosphere are thought to have been broken down to more basic atomic states, leaving no molecules to bond into materials that could potentially reflect any of the incoming solar energy.
Minimal registered reflection
The amount of light an object reflects is called albedo, and WASP-12B never gets higher than 0.064. To put it another way, this means that 94 percent of the energy from the star WASP-12A gets trapped in the planet’s increasingly shattered atmosphere. For comparison, the Earth only absorbs around 70 percent of the Sun’s energy each day, and our rotation helps keep that from being overly concentrated in a single location.
Some energy is reflected though, which is how the Hubble space telescope was able to see the bleak ball of heat in the first place. Once the planet was in it’s brief but daily position where it’d be illuminated by its star, the telescope was able to see and measure the energy reflected off WASP-12B’s daytime side. The light that came back was appropriately slightly red, compatible to the glow of red-hot metal.
My third grader asked: How does the planet exist close to the star at those temperatures? Why wouldn’t it be destroyed like we would be?
Well, the short answer is that WASP-12B is being destroyed, just slowly. Hubble’s Cosmic Origins Spectrograph has found that material from the black ball of heat is being cooked off the atmosphere and absorbed into the star. There aren’t estimates on how long this will continue, but as planet shrinks its inertia will likely decrease, making it even more likely to be consumed by WASP-12A.
Source: Hubble observes pitch black planet, Hubble Space Telescope