This Distant Planet Has a 350,000-Mile-Long Comet-Like Tail

Humanity has spied more than 5,500 worlds orbiting other stars, and some are truly exotic. One seems to have titanium clouds, while on another, storms of glass may rain down.

WASP-69b, a planet orbiting a star 160 light-years away, is the latest addition to the eccentric menagerie. As revealed this week at a meeting of the American Astronomical Society in New Orleans, this exoplanet has a 350,000-mile-long tail of helium gas that billows out behind it like a comet’s.

WASP-69b is slightly larger than Jupiter, although considerably less dense, and it is so close to its star that one full orbit takes just 3.9 Earth days. That makes it what astronomers call a Hot Jupiter, a common type of exoplanet.

Its flamboyant tail, however — which is 50 percent lengthier than the distance between Earth and the moon — is far from quotidian.

As the star’s intense radiation broils WASP-69b, the planet’s atmosphere heats to around 17,500 degrees Fahrenheit and puffs up. The outermost matter of the planet becomes ensnared by the stellar wind and is accelerated into space, eventually reaching speeds of 50,000 miles per hour.

“Most Hot Jupiters are losing mass in this way, but not all of them have tails,” said Dakotah Tyler, a doctoral candidate in astrophysics at University of California, Los Angeles, and an author of an accompanying study published this week in The Astrophysical Journal. “The only way to get the tail is if you have an excessive stellar wind that reshapes and sculpts it, basically like a comet.”