Like a golf ball circling a hole, the planet Kepler-1658b is getting closer and closer to falling into it — its star, that is.
Scientists are watching exoplanet have noted its orbital period around its mature or “evolved” parent star is shrinking over time, suggesting the planets are getting closer to a deadly collision with their star.
“We have previously found evidence that exoplanets inspire their stars, but we have never seen such a planet around an evolved star before,” says Shreyas Vissapragada, an exoplanet scientist at the Harvard and Smithsonian Center for Astrophysics and co-author of a new study on the observations said in a expression (opens in new tab).
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It is quite difficult to determine the orbital decay of exoplanets. The process is quite slow, as astronomers have to wait until they can see many transits of an exoplanet in front of its star. When a planet transits its star, the star appears to dim from the perspective of Earth; Astronomers observing repeated transits can track this eclipse to reconstruct the distant planet’s activity, including its orbital period. Fortunately for Vissapragada and his colleagues, Kepler-1658b has an incredibly short orbital period of 3.8 days, so transits are frequent.
Kepler-1658b is considered “hot Jupiter,” or an exoplanet with a similar mass and size to Jupiter, but a far hotter temperature due to its proximity to its star. It was first discovered by a retired exoplanet hunter from NASA Kepler space telescope in 2009 but was not confirmed as an exoplanet until 2019.
Still, scientists have continuously observed the exoplanet since Kepler discovered it, first with Kepler, then with the Palomar Observatory’s Hale Telescope in California, then NASA’s Transiting Exoplanet Survey Telescope (TESS), launched in 2018 to continue the search for distant planets. During those 13 years, the trio of instruments recorded a steady decrease in Kepler-1658b’s orbital period: 131 milliseconds per year.
Vissapragada and his colleagues now theorize that the orbital breakup is caused by tidal interactions between the exoplanet and its star — the same type of interaction that affects the relationship between Earth and the planet moon. However, in our case, the Earth and Moon are moving further apart due to tidal interactions. In the case of Kepler-1658b, the exoplanet is approaching its star.
“Now that we have evidence that a planet is inspired around an evolved star, we can really start refining our tidal physics models,” Vissapragada said. “The Kepler-1658 system can serve as a sky laboratory in this way for years, and with any luck there will be many more of these laboratories soon.”
The research is described in a paper published Monday (December 19) in the Astrophysical Journal Letters.