WASP-104b: Hot Jupiter Could Be Darkest Planet Ever Discovered

WASP-104b might be the darkest planet ever discovered. Shrouded in a haze that absorbs some 97-99 percent of starlight hitting its surface, researchers think this hot Jupiter-class planet reflects even less light than charcoal.

Scientists from Keele University in Newcastle, UK, explored the gas giant's incredible light-absorbing prowess in a research paper uploaded to the academic preprint server, arXiv.

“From all the dark planets I could find in the literature, this is top five-ish,” researcher Teo Mocnik told New Scientist. “I think top three.”

4_23_Hot Jupiter This image shows an artist's impression of hot Jupiter-class planet. Researchers think hot Jupiter WASP-104b might be one of the darkest planets ever discovered. JPL-Caltech/NASA

WASP-104b and other extremely dark planets—TrES-2b and HAT-P-7b—reflect similarly tiny fractions of light, making it hard to say exactly which is the darkest. The differences are so small its hard to rule out a margin of error in the measurements, New Scientist reported.

WASP-104b has a mass similar to Jupiter’s and an orbit that takes it close to its host star, hence the “hot Jupiter” designation. Most hot Jupiters are pretty dark, ScienceAlert reported, reflecting about 40 percent of the light that hits their surfaces. WASP-104b, however, is an extreme example. 

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The planet is so close to its star that it completes an orbit in just 1.75 days. This cozy distance is key to WASP-104b's impressive darkness as stellar radiation zaps away the planet’s clouds, unlocking potassium and sodium that can soak up starlight.

Astronomers first came across the hot gas giant in 2014 during the Wide Angle Search for Planets project and the Kepler Space Telescope later revealed its impressive appetite for light. Astronomers also observed WASP-104b indirectly as it passed in front of its star and blocked some of the star's light multiple times. This transit tracking revealed key information about WASP-104b, including how much light it was absorbing.

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Undeniably dark, the planet may not actually appear as black as the charcoal comparison might suggest.

“When they say it’s darker than charcoal, it’s being a little misleading,” Adam Burrows of Princeton University, who has been involved in previous work predicting dark planets, told New Scientist. Although it may reflect less light than charcoal, it can still emit some light. More like a bruise, the hot gas giant might glow purple.

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