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Discovery Alert: For This Familiar Planet, a Death Spiral

Illustration shows the dark orb of a hot Jupiter, Kepler-1658 b, crossing in front of its star, very bright and very large as it looms in the background.
Illustration of a previously discovered "hot Jupiter," Kepler-1658 b, that, new data shows, appears to be spiraling into its host star.

The discovery: Kepler-1658 b, a hot Jupiter with a storied history, appears to be spiraling toward its host star – and will likely crash to the star’s surface in less than 3 million years.

Key facts: The deep-fried planet, about as big as our own Jupiter but nearly six times its mass, has a long history with scientists and the public. It was the first planet candidate to be identified by NASA’s Kepler Space Telescope in 2009 – the same year it launched. Those were the early days of surveying exoplanets, or planets around other stars. But doubts about the detection cast Kepler-1658 b into the dustbin of “false positive” exoplanet discoveries. New software and analytical techniques rescued the planet in the years that followed, and placed it in the “confirmed” column by 2019.

Now, only a few short years after it was brought back into the fold, Kepler-1658 b has been consigned to probable oblivion by the latest observations of its orbital path.

Details: Exoplanet scientists deploy an array of techniques to study distant planets, from the “transit” method Kepler used to discover Kepler-1658 b – measuring the tiny dip in starlight as the planet crosses in front of its star – to carefully tracking the wobbles of parent stars, revealing the gravitational tugs of unseen planets. And these techniques continue to grow in refinement. By measuring subtle shifts in the timing of Kepler 1658 b’s transits across the face of its swollen star, a study team determined the planet was arriving earlier than its expected transit times – a key piece of evidence that the planet’s orbit is shrinking.

The team also showed that the giant planet’s decaying orbit is best explained by tidal forces from its parent star, which, as it moves toward its end stage, is expanding. That expansion increases the gravitational interaction between the star and the planet; the star, in a sense, robs the planet’s orbit of its energy.

Our home planet also could meet its end when the Sun grows so large it might swallow Earth, billions of years from now.

Kepler-1658 b also appears to be brighter and hotter than scientists expected, another possible result of tidal interaction with the star.

Fun facts: Hot Jupiters, although among the first exoplanets to be discovered, are strange worlds unlike any in our solar system. They are gas giants, like our own Jupiter, but in extremely tight orbits around their stars – a “year” on these planets, in fact, typically lasts less than 10 days. A year on Kepler-1658 b, once around the star, takes just under four days.

The discoverers: A team led by Shreyas Vissapragada of the Center for Astrophysics Harvard & Smithsonian published the new study of Kepler-1658 b on Dec. 19, 2022, in “The Astrophysical Journal Letters.”