Alien planet spiraling toward its doom could be Earth's future

Thanks to the new observations, the scientific community can now analyze the exoplanet, called Kepler-1658b, to test theories about orbital decay and the very late stages of planetary evolution.

"We've previously detected evidence for exoplanets inspiraling toward their stars, but we have never before seen such a planet around an evolved star," explains Shreyas Vissapragada from the Center for Astrophysics | Harvard & Smithsonian and lead author of a new study detailing the observation. "Theory predicts that evolved stars are very effective at sapping energy from their planets' orbits, and now we can test those theories with observations." 

The scientists, who published their findings in a paper in The Astrophysical Journal Letters, discovered the exoplanet using the planet-hunting Kepler space telescope, which launched into space in 2009.

Kepler-1658b is a hot Jupiter planet, meaning it naturally has a close orbit to its host star. To be precise, Kepler-1658b is located about an eighth of the distance between the Sun and Mercury.

Scientists calculate infinitesimal orbital decay

Astonishingly, the new study shows how the scientists calculated that Kepler-1658b's orbital period is decreasing by an incredibly slow rate of roughly 131 milliseconds (thousandths of a second) per year.

Calculating that minuscule change required 13 years of observation using Kepler, the Palomar Observatory’s Hale Telescope in Southern California, and the Transiting Exoplanet Survey Telescope, or TESS.

All of these observatories captured transits, which is the term used for the amount of time it takes a planet to cross between its host star and Earth, leading to a very slight dimming in the light received from the star.

The scientists point out that the orbital decay of Kepler-1658b is caused by tidal forces between the planet and its host star, causing it to slowly travel inward.

"Now that we have evidence of inspiraling of a planet around an evolved star, we can really start to refine our models of tidal physics," Vissapragada says. "The Kepler-1658 system can serve as a celestial laboratory in this way for years to come, and with any luck, there will soon be many more of these labs." 

The researchers wish to carry out follow-up observations using TESS, which launched into space in 2018. They also hope to uncover other examples of planets nearing a fiery demise on the surface of their host star due to orbital decay.