Astronomers have stumbled upon an exoplanet with a bleak future, spiraling closer to its host star until it is eventually obliterated.
The exoplanet, named Kepler-1658b, was identified in 2019, a decade after the Kepler Space Telescope discovered it as a planet candidate.
The planet is considered a “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. This illustration depicts the exoplanet Kepler-1658b (left), doomed to eventual obliteration by its aging host star. (Center for Astrophysics/Harvard and Smithsonian)
But the orbit is decaying, bringing the planet progressively closer to its star. Eventually, this movement will cause a collision and obliteration of the planet. The Astrophysical Journal Letters published a study detailing the findings on Monday.
“We’ve previously detected evidence of exoplanets being blown into their stars, but we’ve never seen such a planet around an evolved star before,” study lead author Shreyas Vissapragada said in a statement .
“Theory predicts that evolved stars are very effective at reducing the energy of their planets’ orbits, and now we can test these theories with observations.”
After years of observations with space and ground-based telescopes, the researchers calculated that the planet’s orbit is decreasing at a rate of 131 milliseconds per year. The telescopes observed dips in the star’s brightness as the planet passed by. The intervals between these dips, called transits, have steadily decreased as the orbit has decayed.
As an exoplanet, Kepler1658b’s structure is very different from Earth’s, as seen in this comparison with exoplanet Kepler138d. (Benoit Gougeon/University of Montreal)
The role of gravitational attraction
Tidal interactions, or the gravitational relationship between Kepler-1658b and its star, are to blame for the planet’s inward pull. Astronomers are still learning about the gravitational interactions between orbiting bodies, such as Earth and the Moon, but this planetary system could shed light on these dynamics.
The new research also helped the researchers potentially explain why Kepler-1658b appears even hotter and brighter than expected. The same gravitational pull between the planet and its star may also be releasing additional energy from the planet.
“What we realized during this study is that the planet could be bright because it is much hotter than previously expected, 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.
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“I’m excited to study this possibility further: Are we witnessing the last gasp of a doomed planet?”
Not unlike 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 the surface of this moon. The Juno mission will conduct several flybys of Io over the next year and a half to learn more about this volatile relationship.
Observation of other exoplanets at risk
Meanwhile, the aging star that Kepler-1658b orbits is expanding and entering its subgiant phase before becoming a red giant, a dying star in the final stages of life.
The findings could foretell the fate of planets in our own solar system that may one day find themselves too close to the sun.
“In five billion years or so, 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.”
Stars enter the red giant phase when they are close to death. (Adam Makarenko/WM Keck Observatory)
Researchers believe more exoplanets are in danger of dying in the burning light of their respective host stars, and observations of them may be just around the corner using TESS, or the Exoplanet Survey Satellite in transit, which studies the light of nearby stars.
“The Kepler-1658 system can serve as a celestial laboratory in this way for years to come,” Vissapragada said.
“And hopefully, there will be many more of these labs soon.”