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Astronomers have stumbled upon an exoplanet with a bleak future that is spiraling closer to its parent star before eventually becoming extinct.
The exoplanet named Kepler-1658b was identified in 2019, a decade after the Kepler space telescope spotted it as a planet candidate.
The planet is considered “hot Jupiter,” or a type of exoplanet similar in size to Jupiter – but with a scorching temperature. Kepler-1658b closely orbits its aging star, completing a single orbit every 3.85 days.
But the orbit is decaying, causing the planet to gradually approach its star. Finally this movement will lead to a collision and the annihilation of the planet. The Astrophysical Journal Letter published a study Monday detailing the findings.
“We have already discovered evidence of exoplanets spiraling towards their stars, but we have never seen such a planet orbiting an evolved star before,” said the study’s lead author Shreyas Vissapragada, a 51 Pegasi b fellow at the Center for Astrophysics | Harvard & Smithsonian, in a statement.
“The theory predicts that evolved stars are very effective at siphoning energy from their planets’ orbits, and now we can test these theories with observations.”
After years of observations with Using both space-based and ground-based telescopes, researchers calculated that the planet’s orbit is decreasing at a rate of 131 milliseconds per year. The telescopes searched for dips in brightness from the star as the planet passed in front of it. The intervals between these dips, called transits, have steadily decreased as the orbit has decayed.
Tidal interactions, or the gravitational relationship between Kepler-1658b and its star, are responsible for the planet’s inward pull. Astronomers are still learning about the gravitational interactions between orbiting bodies like the Earth and the Moon, but this planetary system could shed light on those dynamics.
The new research may also have helped researchers explain why Kepler-1658b appears even hotter and brighter than expected. The same gravitational pull between the planet and its star can also release additional energy from the planet.
“What we realized during this study is that the planet could be bright because it’s much hotter than previously thought, which could happen if the same effects that drive the decay of the planet’s orbit also heat it up,” Vissapragada said in an email. “I look forward to further investigating this possibility: are we witnessing the last gasp of a doomed planet?”
It is not dissimilar to Jupiter’s moon Io, the most volcanic place in our solar system. Jupiter’s strong gravitational influence is melting the interior of Io, causing lava to erupt from hundreds of volcanoes on this moon’s surface. The Juno mission will conduct multiple flybys of Io over the next year and a half to learn more about this volatile relationship.
Meanwhile, the aging star orbiting Kepler-1658b is expanding and contracting its subgiant phase before becoming a red giant, a dying star in the final stages of life. The results could potentially preview the fate of planets in our own solar system that may one day find themselves too close to the Sun.
“In about five billion years, the Sun will evolve into a red giant star,” Vissapragada said. “It seems certain that Mercury and Venus will be engulfed during this process, but what happens to Earth is less clear.”
Researchers believe other exoplanets are at risk of dying in the fiery light of their respective host stars, and observations of them could be just around the corner with TESS or the Transiting Exoplanet Survey Satellite, which studies the light from nearby stars.
“The Kepler-1658 system can thus serve as a heavenly laboratory for years to come,” Vissapragada said, “and with any luck, there will be many more of these laboratories soon.”
