Astronomers Catch a Glimpse of a Pitch-Black Planet
by Joel Hruska
Historically, hot Jupiters — gas giant planets that orbit close to their home stars — have been a bit of a problem for our models of the solar system. When they started popping up in our extrasolar planet detection systems, it was initially thought these planets were anomalies that appeared to be more common than they really were because our detection mechanisms favored them. That’s become less likely as the number of exoplanets we’ve positively identified has risen; with more than 2,000 exoplanets identified today, hot Jupiters are clearly common. They’re also occasionally weird in ways we don’t expect. Scientists working to detect planets have found that one Hot Jupiter, identified as WASP-12b, is the blackest planet known to exist, absorbing 94 percent of visible light.
WASP-12b is unique for multiple reasons. It’s so close to its host star that it orbits slightly less than once per day (1.09 days per orbit). WASP is a trinary star system with one yellow dwarf star similar to our sun and two red dwarfs at roughly 37 percent and 38 percent of the sun’s mass. To put that in perspective, Mercury is easily the fastest planet in our own solar system, but it takes 88 days to orbit the sun. WASP is 1.57x larger than the sun, which means WASP-12b is orbiting at incredible velocities. Scientists have previously found that the planet is being actively consumed and has already stretched into an egg shape, and will likely be destroyed within the next ten million years.
A new survey has found that the surface temperature in the atmosphere is up to 4,600 degrees Fahrenheit, which means that one side of the planet likely has no clouds at all; there’s too much heat for clouds to form. Instead, light beams deep into the atmosphere and is absorbed. On the far side of the planet, the temperature is as much as 2,000 degrees cooler, which allows for the formation of cloud systems. This kind of wild atmospheric temperature differential and the completely different characteristics of the atmosphere has been previously suspected for hot Jupiters and those planets that sit so close to their home star as to be tidally locked to it, but most hot Jupiters reflect about 40 percent of the starlight they receive. This one doesn’t. HubbleSite.org spoke to Taylor Bell of McGill University and the Institute for Research on Exoplanets in Montreal, Quebec, Canada, who said:
This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters…You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they’re both called hot Jupiters. Past observations of hot Jupiters indicate that the temperature difference between the day and night sides of the planet increases with hotter day sides. This previous research suggests that more heat is being pumped into the day side of the planet, but the processes, such as winds, that carry the heat to the night side of the planet don’t keep up the pace.
One of the fundamental precepts of physics and astronomy is the idea that the universe looks pretty much the same in every direction, with some local variations on the small (by galactic standards) scale. To date, our own solar system bucks that trend. This could be entirely explained by our own limited equipment; our ability to detect large planets is much better than our ability to detect small ones. Still, we have yet to find a solar system with a similar distribution of planets at equivalent distances around a similar star. TRAPPIST-1 is probably the closest, and there are still substantial differences between the two.
The role hot Jupiters play in the formation of solar systems is still a topic of considerable debate, so expect to see a robust conversation on the topic in the years ahead. Meanwhile, WASP-12b is a gas giant in the process of being eaten by its host star — a fascinating discovery in its own right, along with its unusual thermal and reflective properties.
Originally published at www.extremetech.com on September 18, 2017.