Chinese scientists reveal surviving exoplanets in "theoretical forbidden zone"

China News Service, Kunming, October 27 (Reporter Chen Jing) Yunnan University reported on the 27th that Qian Shengbang, a professor at the school of physics and astronomy, and his team published a paper pointing out that three exoplanets that should have been swallowed by the host star are still surviving in the "theoretical forbidden area" of stellar evolution, revealing a "survival paradox" that contradicts the classic engulfment theory. The discovery of several specimens suggests that the phenomenon may have a common physical origin that goes beyond particular cases.

Stars similar to the sun will evolve and expand into red giants after the central hydrogen core fuel is exhausted. Nearby planets may be directly swallowed by the expanding outer layer, or they may lose orbital energy due to tidal effects and gradually fall toward the host star and be swallowed up.

Qian Shengbang's team used asteroseismological analysis of the weak changes in the brightness of the three exoplanet host stars 24 Boo, HD12648 and TYC4282-605-1 to confirm that the three host stars have entered the core helium burning stage.

Under the constraints of starquakes and orbital observations, the team used stellar evolution models to trace the past evolutionary expansion ranges of the three host stars and compared them with the current planetary orbits. The study found that their orbital scales were all within the past expansion range of the star, and they all fell into the theoretical engulfment region, revealing that these three exoplanets should all be swallowed up by their red giant host stars and would be difficult to survive.

This study extends the survival paradox of close planets from a single case to multiple systems. A "survivor" may originate from a rare binary star interaction or other special history; the occurrence of similar contradictions in multiple systems prompts the need to find evolutionary channels that can occur repeatedly in different systems, providing a new basis for testing common physical processes that may be missed by classical models.

The sun will also go through a red giant evolution stage in the future. These findings reveal that the long-term fate of the solar system, including the earth, may be more complicated than predicted by classical theories.

The paper was published in the Proceedings of the National Academy of Sciences (PNAS) and is titled "The Survival Paradox of Close-In Planets Orbiting Red Clump Giants." Lin Wenxu, a postdoctoral fellow at the School of Physics and Astronomy of Yunnan University, is the first author of the paper, and Qian Shengbang is the independent corresponding author. Researchers from Yunnan University, Yunnan Observatory of the Chinese Academy of Sciences and other units jointly participated in this study.