Astronomers have discovered that aging stars expanding into red giants are engulfing close-orbiting giant planets. A study of nearly half a million stars shows fewer such planets around more evolved red giants, suggesting many have been destroyed. The findings come from data collected by NASA's Transiting Exoplanet Survey Satellite.
Researchers led by Dr. Edward Bryant at the Mullard Space Science Laboratory, affiliated with University College London and the University of Warwick, analyzed observations of nearly 500,000 stars in their post-main-sequence phase. They identified 130 planets and planet candidates in tight orbits of up to 12 days, including 33 newly detected ones. The study, published in the Monthly Notices of the Royal Astronomical Society, reveals a clear decline: 0.35% of younger post-main-sequence stars host these giants, dropping to 0.11% for more evolved red giants. 48 were confirmed planets, 49 prior candidates, and the rest new discoveries after filtering over 15,000 signals for false positives. Fewer close-in giants around advanced stars points to destruction by tidal interactions, Dr. Bryant explained. As stars expand, gravitational tugs slow planets, shrinking their orbits until they spiral in and break apart or fall into the star. We were surprised by just how efficient these stars seem to be at engulfing their close planets, he said. Co-author Dr. Vincent Van Eylen noted implications for our solar system. In a few billion years, our Sun will become a red giant, he said. Earth might survive the early phase, unlike the giant planets studied, but life on it probably would not. The team used NASA's TESS to detect transits—tiny dips in starlight from planets passing in front. Future mass measurements will refine understanding of the spiraling process. Funding came from the UK Science and Technology Facilities Council.