At the end of our sun’s lifetime, it will expand 100 times as much as it does now and engulf the Earth. Many planets in other solar systems face a similar death as their stars age. But all hope is not lost, as astronomers at the University of Hawaii Institute for Astronomy (UH IfA) have made a startling discovery about the planet’s survival after an event that should have been certain death at the hands of its sun.

The Jupiter-like planet 8 UMi b, officially named Halla, orbits the red giant star Baekdu (8 UMi), only half the distance separating the Earth from the Sun. Using two Maunakea observatories on the island of Hawaii (the WM Keck Observatory and the Canada-France-Hawaii Telescope (CFHT)), a team of astronomers led by Mark Hohn, NASA Hubble Fellow at UH IfA, found that Baekdu’s normally dangerous evolution

Using observations of Baekdu’s stellar oscillations from NASA’s Transiting Exoplanet Survey Satellite (TESS) satellite, they found that the star burned helium in its core, indicating that it once massively transformed into a red giant. The work was published in the journal. Nature.

The star inflated to 1.5 times the planet’s orbital distance and engulfed the planet in the process before shrinking to its current size by just one-tenth of that distance.

“The absorption of a planet has disastrous consequences for either the planet or the star itself, or both. The study’s lead author, Hohn, said: “The fact that Halley managed to survive near a giant star that would otherwise devour it highlights that the planet is an outstanding survivor.”

Maunakea observatories confirm survivors

Hull’s planet was discovered in 2015 by a team of astronomers from Korea using the radial velocity method, which measures the periodic motion of a star due to the gravity of a rotating planet. After discovering that the star must once have been larger than the planet’s orbit, the IfA team made additional observations from 2021 to 2022 using the Keck Observatory’s High Resolution Echelle Spectrometer (HIRES) and the CFHT ESPaDOnS instrument. These new data confirm that the planet’s 93-day, near-circular orbit has remained stable for more than a decade, and that changes in radial velocity must originate from the planet.

“Together, these observations confirmed the existence of the planet and left us with the overwhelming question of how the planet actually survived,” said IfA astronomer Daniel Huber, second author of the study. “Observations from several telescopes on Maunakea were critical in this process.”

Escape from absorption

At 0.46 AU (astronomical units or Earth-Sun distance) from its star, the planet Hulles looks like “hot” or “hot” Jupiter-like planets thought to enter larger orbits before migrating inward close to their star. However, in the face of a rapidly evolving host star, such an origin becomes an extremely unlikely path for planet Galla’s survival.

Another theory for the planet’s survival is that it never faced the threat of being engulfed. The team believes that Baekdu’s main star may actually be two stars, like the famous Star Wars planet Tatooine orbiting two suns. The merger of these two stars could prevent any of them from expanding enough to swallow a planet.

A third possibility is that Halla was relatively newborn, meaning that as a result of the powerful collision between the two stars, a gas cloud formed from which the planet was formed. In other words, the planet Hull could be a newborn “second generation” planet.

“Most stars are in binary systems, but we still don’t fully understand how planets form around them. Therefore, it is likely that more planets exist around highly developed stars due to binary interaction,” explained Hon. Source