Puffiest Planet

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Puffiest Planet

A giant planet in the constellation Hercules sounds like it would make a sweet snack for the strongman. It’s about as dense as cotton candy. In fact, it may be the “puffiest” planet yet seen.

HAT-P-67b is about 1200 light-years away. Its star — HAT-P-67 — is bigger, brighter, and heavier than the Sun. And the star and planet are quite close together — a tiny fraction of the distance from Earth to the Sun. That means the planet is getting roasted. The temperature at its cloud tops is at least 3,000 degrees Fahrenheit. And some recent work says it could be 8500 degrees or higher — hotter than most of the stars in the galaxy.

The heat has caused the planet’s outer layers to puff up. HAT-P-67b is about a third as massive as Jupiter, the giant of our own solar system. But it’s more than twice Jupiter’s diameter. That means it’s big and puffy. It’s only about five percent as dense as water — roughly the density of cotton candy.

The parent star may be blowing away the planet’s atmosphere — a process that could make the planet even puffier.

The HAT-P-67 system is in Hercules, which is high in the west at nightfall. The system stands to the right of the Keystone — four moderately bright stars that outline the strongman’s body. But the system is too faint to see without a telescope.

Tomorrow: “computing” a career in astronomy.

Script by Damond Benningfield

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