Like a golf ball circling a hole, the planet Kepler-1658b is getting closer and closer to falling in — into its star, that is.
Scientists observing the exoplanet have noticed its orbital period around its mature or "evolved" parent star is shrinking over time, indicating that the planets inching closer to a fatal collision with its star.
"We've previously detected evidence for exoplanets inspiraling toward their stars, but we have never before seen such a planet around an evolved star," 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 statement.
Related: Last light: Here's the final view from NASA's planet-hunting Kepler Space Telescope
It's rather difficult to determine the orbital decay of exoplanets. The process is quite slow, as astronomers must wait to see many transits of an exoplanet in front of its star. As a planet transits its star, the star appears to dim from the perspective of Earth; astronomers observing repeated transits can track that dimming to reconstruct the distant planet's activities, including its orbital period. Fortunately for Vissapragada and his colleagues, Kepler-1658b has an incredibly short orbital period of 3.8 days, so transits happen frequently.
Kepler-1658b is considered a "hot Jupiter," or an exoplanet with a similar mass and size as Jupiter, but a far hotter temperature due to its close proximity to its star. It was first spotted by NASA's retired exoplanet-hunter Kepler Space Telescope in 2009, but was not confirmed to be an exoplanet until 2019.
Still, scientists have been continuously observing the exoplanet since Kepler spotted it, first using Kepler, then the Palomar Observatory's Hale Telescope in California, then NASA's Transiting Exoplanet Survey Telescope (TESS) that launched in 2018 to carry on the work of finding distant planets. During those 13 years, the trio of instruments has recorded a steady decrease in Kepler-1658b's orbital period: 131 milliseconds per year.
Vissapragada and his colleagues now theorize that the orbital decay is caused by tidal interactions between the exoplanet and its star — the same type of interaction that affects the relationship between Earth and the moon. In our case, however, the Earth and the moon are becoming more distant due to tidal interactions. In the case of Kepler-1658b, the exoplanet is getting closer to its star.
"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 said. "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 research is described in a paper published Monday (Dec. 19) in the Astrophysical Journal Letters.
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More exoplanets like this are found now potentially sprialing into their parent stars on very short time scales.
Aging Ungracefully, Sky & Telescope 145(1):14-19, 2023
"IMMINENT DEMISE If planets stayed put until their stars swelled to engulf them, then the hot Jupiter WASP-12b would have about 2 billion years in its future. But observations reveal that the planet’s orbit is decaying rapidly — in only 3 million years, it will plunge into the star."
Newly-found planets on the edge of destruction, https://www.sciencedaily.com/releases/2022/01/220113151415.htm
"Summary: Astronomers have found three Jupiter-like exoplanets that are dangerously close to being 'swallowed up' by their host stars. The discovery gives new insight into how planetary systems evolve over time, helping to reveal the fate of solar systems like our own." "Three newly-discovered planets have been orbiting dangerously close to stars nearing the end of their lives. Out of the thousands of extrasolar planets found so far, these three gas giant planets first detected by the NASA TESS (Transiting Exoplanet Survey Satellite) Mission, have some of the shortest-period orbits around subgiant or giant stars. One of the planets, TOI-2337b, will be consumed by its host star in less than 1 million years, sooner than any other currently known planet..."
This doomed alien planet has a year that lasts just 16 hours — it's only getting faster, https://forums.space.com/threads/this-doomed-alien-planet-has-a-year-that-lasts-just-16-hours-%E2%80%94-its-only-getting-faster.51570/
Seems like some exoplanets observed today have very short lifetimes compared to stellar evolution model ages extending time back millions and billions of years for various stars and clusters.
So, our searches for planets are likely to result in a population of detected exoplanets with an over-representation of these large planets very close to stars.
It would be useful to know how biased this sample is. I guess we really won't know until we can see most of the planets around most of the stars.