This Exoplanet Is Doomed to Be Obliterated by a Star

Kepler-1658b is slowly spiraling toward a fiery demise

illustration of a jupiter-like planet and fiery yellow star
Kepler-1658b was the first exoplanet discovered by NASA’s Kepler Space Telescope in 2009. Gabriel Perez Diaz / Instituto de Astrofísica de Canarias

More than a decade ago, Kepler-1658b was the first exoplanet discovered by NASA’s Kepler Space Telescope. Now, astronomers say the planet is doomed to meet a fiery fate. It’s been spiraling ever closer to its host star, foreshadowing a fatal collision.

This is the first time astronomers have observed an exoplanet inching closer to an evolved, or older star, according to a statement from the Center for Astrophysics, Harvard & Smithsonian. Researchers detailed the exoplanet’s impending demise in a study published Monday in The Astrophysical Journal Letters.

“We’ve previously detected evidence for exoplanets inspiraling toward their stars, but we have never before seen such a planet around an evolved star,” says lead author Shreyas Vissapragada, a 51 Pegasi b Fellow at the Center for Astrophysics, Harvard & Smithsonian. “Theory predicts that evolved stars are very effective at sapping energy from their planets’ orbits, and now we can test those theories with observations.”

Nicknamed a “hot Jupiter,” Kepler-1658b is a gas giant that orbits extremely close to its host star, despite being similar to Jupiter in mass and size. The exoplanet’s orbit is about eight times closer than that of Mercury, the planet nearest to the sun in our solar system—and it’s moving closer still.

The research revealed that Kepler-1658b’s orbit is declining by 131 milliseconds per year. This process, called orbital decay, is slow and gradual. It took years of close observation by space- and ground-based telescopes to detect this miniscule change. But together, three telescopes captured transits, or moments when the host star’s brightness appears to dim as the planet passes between it and the Earth. Astronomers determined the amount of time between these transits has been slowly shrinking over the last 13 years.

Tides are the culprit behind Kepler 1658b’s orbital decay. These gravitational interactions between the planet and its host star might also account for why the gas giant is hotter and brighter than expected: As tidal relationships decrease the planet’s orbit, they may release additional energy within the exoplanet, according to the statement.

This burst of light and heat may be “the last breath of a condemned planet,” Vissapragada tells CNN’s Ashley Strickland in an email.

While this find is novel, lots of other planets with similar orbits likely exist. After all, the Kepler Space Telescope spotted 2,650 exoplanets before it retired four years ago, which accounted for about 70 percent of all the known worlds outside our solar system at the time, reported Jason Daley for Smithsonian magazine in 2018. With the Transiting Exoplanet Survey Satellite, a current mission intended to discover thousands of exoplanets, researchers expect to find even more worlds that may collide with their host stars.

For now, Kepler-1658b’s aging host star continues to expand, and one day it will become a red giant—a large, dying star nearing its final life stage. The exoplanet offers a glimpse into the “death-by-star” phenomenon, a fate that could eventually await Earth billions of years from now, as our sun gets older and expands, according to the statement.

“In five billion years or so, the sun will evolve into a red giant star,” Vissapragada tells CNN. “It seems certain that Mercury and Venus will be engulfed during this process, but what happens to the Earth is less clear.”