Pitch Black Exoplanet: Hot Jupiter WASP-12b Reflects No Light
WASP-12b, which was discovered in 2008 is one of the best-studied exoplanets. It circles the sun-like star WASP-12A located about 1,400 light years away.
The planet, categorized as a hot Jupiter, has a radius nearly twice that of Jupiter. It orbits very close to its host star that its one year is equivalent to just over than one Earth day.
The close proximity caused the gravitational pull of WASP-12A to stretch WASP-12b into an egg-like shape and increased the surface temperature of the planet's daylight side to 2600 degrees Celsius.
To know more about the planet's atmospheric composition, researchers measured the amount of light that WASP-12b reflects, known as the albedo.
Scientists observed the planet in 2016 during an eclipse when it was near full phase and passed behind its parent star. This method is considered the best way to determine the albedo of a planet since this involves directly measuring the amount of light that the object reflected.
Now, Taylor Bell, from McGill University University in Canada, and colleagues used the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to measure WASP-12b's albedo at several different wavelengths.
The researchers found that the planet's albedo is 0.064 at most, which means that the planet is darker than fresh asphalt. It also suggests that the exoplanet is likely two times less reflective than the Earth's moon, which has an albedo of 0.12.
Researchers said that the high temperature is likely the reason behind the planet's low albedo. Hot clouds cannot form, and alkali metals get ionized because of the extremely hot temperature of the planet's daylight side. The temperature is also hot enough to break up hydrogen molecules into atomic hydrogen causing the atmosphere to behave more like that atmosphere of a low-mass star, which is attributed for the low albedo of the planet.
Different From Hd 189733b
The other hot Jupiter with spectrally resolved albedo measurements is HD 189733b. HD 189733b was observed to have deep blue color and is different from WASP-12b. Researchers said that WASP-12b does not appear to show a color preference in the light that it reflects and rather glows red like a hot glowing metal because of its heat.
"Our results are in stark contrast with those for the much cooler HD 189733b, the only other hot Jupiter with spectrally resolved reflected light observations," the researchers wrote in their study.