For those who like to drive, nothing is quite as inviting as a freshly-applied (and dried) blacktopped road. Do space travelers feel the same way about a completely black planet that is dark enough to disappear and absorbs everything its nearby star shines at it? What fresh hole in space is this? Has an alien civilization invented a planetary cloaking device?
The discovery of the lack of light on the dark exoplanet was announced this week by NASA and the European Space Agency. The obsidian orb is WASP-12b and it was actually discovered in 2008 orbiting WASP-12, a magnitude 11 yellow dwarf star located approximately 1400 light-years away in the constellation Auriga. While WASP-12 is about the size of our Sun, WASP-12b is what NASA calls a “hot Jupiter,” which sounds like an astronaut exclamation (Hot Jupiter, Spock! Who cares if she’s green … she’s gorgeous!”) but is slang for a large (in this case, twice the diameter of our Jupiter), hot, gaseous planet (also called a roaster planet) with a quick orbit – WASP-12b makes its circuit in just 10 days. That makes it so incredibly hot (2600 degrees Celsius on its daylight side) that its star’s pull is able to mold the exoplanet into an egg shape.
Astronomers from McGill University, Canada and the University of Exeter, UK, used the Hubble space telescope to observe WASP-12b during an eclipse (theirs, not ours) when it passed behind its sun. Taylor Bell, a Master’s student in astronomy at McGill University and lead author of the report, explains what they saw:
“The measured albedo of WASP-12b is 0.064 at most. This is an extremely low value, making the planet darker than fresh asphalt!”
Hot Jupiter, Taylor! What’s an albedo?
Latin for “whiteness,” albedo is a measurement of reflection. While other colder exoplanets have low albedos due to clouds or surface alkali metals, WASP-12b’s extreme heat means it has neither of these. Its super-low albedo is caused by its super-hot temperature which breaks down its hydrogen molecules into hydrogen atoms, allowing WASP-12b to reflect almost no light – it eats 94% of it. This gives this hot Jupiter a dark red hue, contrasting it to another hot Jupiter, HD 189733b, which has a higher albedo, making it deep blue and causing astronomer Bell to wax philosophically:
“The fact that the first two exoplanets with measured spectral albedo exhibit significant differences demonstrates the importance of these types of spectral observations and highlights the great diversity among hot Jupiters.”
Does that dark color make WASP-12b an attractive asphalt roadish planet just begging for a landing? Would the first crew to touch down paint white stripes or parking lot lines? Would that make the residents on the cooler side yell “Hot Jupiter! Why didn’t we think of that!”
At 1400 light years away, we'll probably never know.