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Exoplanet Is Pitch-Black, Astronomers Find

Photo from NASA

Astronomers have found that the exoplanet WASP-12b reflects almost no light, making it appear pitch black.

An international team of astronomers from McGill University in Canada and the University of Exeter in the United Kingdom used the Space Telescope Imaging Spectrograph (STIS) on the NASA/ESA Hubble Space Telescope to measure how much light the exoplanet was reflecting in order to learn more about its atmosphere, Science Daily reports.

What they found surprised them, according to lead author Taylor Bell, a Master’s student in astronomy at McGill University who is also affiliated with the Institute for Research on Exoplanets. Bell says, “The measured albedo of WASP-12b is 0.064 at most. This is an extremely low value, making the planet darker than fresh asphalt!” Albedo refers to the light the planet reflects. This means WASP-12b is two times less reflective than the moon. Bell adds,

The low albedo shows we still have a lot to learn about WASP-12b and other similar exoplanets.

Since the planet was discovered in 2008, it has become one of the most studied of its kind. WASP 12-b orbits around the larger WASP-12A some 1400 light-years away from Earth. WASP 12-b has a radius almost two times the size of Jupiter’s, and has a year equivalent to one Earth day. Its proximity to its parent star has let the gravitational pull of WASP-12A stretch WASP-12b into an egg shape. Its surface temperature is around 2600 degrees Celsius on the daylight side.

This extremely hot temperature may also account for the exoplanet’s low albedo. Bell explains, “There are other hot Jupiters that have been found to be remarkably black, but they are much cooler than WASP-12b. For those planets, it is suggested that things like clouds and alkali metals are the reason for the absorption of light, but those don’t work for WASP-12b because it is so incredibly hot.”

The scientists observed the exoplanet during an eclipse in 2016, and measured its albedo. Nikolay Nikolov of the University of Exeter says, “After we measured the albedo we compared it to spectral models of previously suggested atmospheric models of WASP-12b. We found that the data match neither of the two currently proposed models.”

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