Scalding hot gas giant breaks heat records

The planet KELT 9b is so hot — hotter than many stars — that it shatters gas giant temperature records, researchers report online June 5 in Nature.

This Jupiter-like exoplanet revolves around a star just 650 light-years away, locked in an orbit that keeps one side always facing its star. With blistering temps hovering at about 4,300^o Celsius, the atmosphere on KELT 9b’s dayside is over 700 degrees hotter than the previous record-holder — and hot enough that atoms cannot bind together to form molecules.

“It’s like a star-planet hybrid,” says Drake Deming, a planetary scientist at the University of Maryland in College Park who was not involved in the research. “A kind of object we’ve never seen before.”

KELT 9b also boasts an unusual orbit, travelling around the poles of its star, rather than the equator, once every 36 hours. And radiation from KELT 9b’s host star is so intense that it blows the planet’s atmosphere out like a comet tail — and may eventually strip it away completely.

The planet is so bizarre that it took scientists nearly three years to convince themselves it was real, says Scott Gaudi of Ohio State University. Deming suspects KELT 9b is “the tip of the iceberg” for an undiscovered population of scalding-hot gas giants.