Planet Halla Defies Death at the Hands of Its Sun, University of Hawaii Astronomers Discover
Astronomers from the University of Hawaii Institute for Astronomy have made an astonishing discovery – a planet that has survived an event that should have spelled certain doom. When the Sun nears the end of its life, it will expand to a size 100 times its current size, engulfing the Earth and other planets in its path. Many planets in other solar systems face a similar fate as their host stars age. However, researchers have found a planet that has defied this fate – Halla, a Jupiter-like planet that orbits the red giant star Baekdu.
In a study published in the journal Nature, a team of astronomers led by Marc Hon, a NASA Hubble Fellow at the University of Hawaii Institute for Astronomy, revealed their findings. Through observations using the W. M. Keck Observatory and the Canada-France-Hawaii Telescope (CFHT) on Hawaii’s Maunakea island, the team discovered that Halla managed to survive despite Baekdu’s expansion.
Baekdu, officially known as 8 UMi, had already expanded into a red giant star once before, burning helium in its core. The star would have grown to 1.5 times the distance of Halla’s orbit, which should have resulted in the planet’s engulfment. However, the planet miraculously persisted in the immediate vicinity of the giant star.
“The fact that Halla has managed to persist in the immediate vicinity of a giant star that would have otherwise engulfed it highlights the planet as an extraordinary survivor,” said Hon, the lead author of the study.
The discovery of Halla was made in 2015 by a team of astronomers from Korea using the radial velocity method. The team from the University of Hawaii Institute for Astronomy conducted additional observations from 2021 to 2022 using the Keck Observatory’s High-Resolution Echelle Spectrometer and CFHT’s ESPaDOnS instrument. These observations confirmed Halla’s existence and stability, leaving the astronomers with the question of how the planet managed to survive.
One possibility is that Halla never faced the danger of engulfment because its host star, Baekdu, may have originally been two stars that merged. This merger could have prevented either of the stars from expanding to a size that would engulf the planet. Another theory is that Halla is a relatively new planet that formed from a gas cloud produced by the collision of the two stars. This would make Halla a “second generation” planet.
The remarkable survival of Halla raises questions about planetary evolution and the potential for planets to exist around highly evolved stars due to binary interactions. According to Hon, “It’s plausible that more planets may actually exist around highly evolved stars thanks to binary interactions.”
The observations from the Maunakea observatories were critical in confirming the survival of Halla. Daniel Huber, an astronomer at the University of Hawaii Institute for Astronomy and a second author of the study, emphasized the importance of the multiple telescopes’ data in the discovery.
The study, titled “A close-in giant planet escapes engulfment by its star,” was authored by Marc Hon, Daniel Huber, and a team of researchers from various institutions. It was published on June 28, 2023, in the journal Nature.