NASA’s Hubble Space Telescope has observed a planet outside our solar system that looks as black as fresh asphalt because it eats light rather than reflecting it back into space. The exoplanet, called WASP-12b, is one of a class of so-called “hot Jupiters,” gigantic, gaseous planets that orbit very close to their host star and are heated to extreme temperatures.
This light-eating prowess is due to the planet’s unique capability to trap at least 94 per cent of the visible starlight falling into its atmosphere, said a study published in the Astrophysical Journal Letters. “We did not expect to find such a dark exoplanet,” said lead researcher Taylor Bell of McGill University and the Institute for Research on Exoplanets in Montreal, Quebec, Canada. “Most hot Jupiters reflect about 40 per cent of starlight,” Bell said.
WASP-12b is about two million miles away from its star and completes an orbit once a day. It circles a Sun-like star residing 1,400 light-years away in the constellation Auriga. The planet’s atmosphere is so hot that most molecules are unable to survive on the blistering day side of the planet, where the temperature is 2537.7 degrees Celsius.
Therefore, clouds probably cannot form to reflect light back into space. Instead, incoming light penetrates deep into the planet’s atmosphere where it is absorbed by hydrogen atoms and converted to heat energy. But the planet’s nighttime side is a different story. WASP-12b has a fixed day side and night side because it orbits so close to the star that it is tidally locked.
The nighttime side is more than 1093 degrees Celsius cooler, which allows water vapour and clouds to form. “This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters,” Bell said.