Astronomers from the University of Hawaii Institute for Astronomy have made an intriguing discovery of a planet that survived what should have been a catastrophic event caused by its host star. The planet, officially named Halla and also known as 8 UMi b, orbits the red giant star Baekdu (8 UMi) at a distance half that of Earth to the Sun. Typically, when stars like Baekdu grow old and expand to become red giants, planets in their vicinity face certain demise. However, the planet Halla has managed to persist despite the perilous evolution of its star.
The research team, led by Marc Hon, a NASA Hubble Fellow at the University of Hawaii Institute for Astronomy, used observations from the W. M. Keck Observatory and the Canada-France-Hawaii Telescope (CFHT) on Hawaii Island to study the star Baekdu and its planetary companion. They analyzed Baekdu’s stellar oscillations observed by NASA’s Transiting Exoplanet Survey Satellite and found that the star had already expanded into a red giant once before, burning helium in its core.
According to the study published in the journal Nature, Baekdu would have swelled to 1.5 times the distance between the planet and the star, engulfing the planet in the process. However, it then shrunk back to its current size, which is only one-tenth of that distance. The fact that the planet Halla has managed to survive in the immediate vicinity of a star that should have engulfed it is considered remarkable.
The discovery of Halla was made in 2015 by a team of astronomers from Korea using the radial velocity method. The University of Hawaii team conducted additional observations using high-resolution spectroscopy instruments, confirming the stability of Halla’s orbit and its persistence for more than a decade.
This discovery highlights the resilience of certain planets in the face of extreme stellar evolution. It provides valuable insights into the survival mechanisms of planets and expands our understanding of planetary dynamics in different stellar systems.