Planet Halla survives as nearby star morphs into a red giant, astonishing astronomers

Stars, including our Sun, undergo various stages due to their ageing process. Still, viewed from a terrestrial timeframe, these transformations take an extremely long time. For our Sun, the next stage, where it devolves into a red giant, and subsequently a white dwarf, then a black dwarf, is anticipated to occur in around 5 billion years.

Astronomers conjecture that at this stage, the Sun will expand its size by a hundredfold and engulf nearby planets - Mercury, Venus, and likely Earth. Even if Earth somehow endures, the close proximity of the Sun will cause it to experience extremely high temperatures. However, a planet spotted by astronomers from the University of Hawaiʻi Institute for Astronomy (UH IfA) successfully withstood the evolvement of its neighbouring star.

Data gathered by the WM Keck Observatory and Canada-France-Hawaiʻi Telescope (CFHT) on the island of Hawaiʻi facilitated this finding. They determined that the planet, named Halla, which is reminiscent of Jupiter, orbits a red giant star, Baekdu, at half the distance between our own planet and the Sun, and maintains a stable state despite its proximity to its evolving star.

The astronomers, aided by observations from NASA's Transiting Exoplanet Survey Satellite (TESS), noticed that the star is combusting helium in its core. A report by Phys.org published in 2023 pointed out that this is an indication that the star has undergone a size expansion and transitioned into a red giant. This type of planetary consumption has devastating consequences for both the planet and the 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," stated the astronomers.

The scientists eliminated the possibility that Halla may never have existed. They suggested two plausible scenarios explaining its unusual endurance. As articulated by Science Alert, one presumption is that Baekdu was once a binary star. The merging of these two stars could have led to the immediate ignition of helium combustion, skipping the red giant phase, thus eliminating the threat to the planet.

Alternatively, the researchers hypothesized that Halla could be a newly formed planet. It could have been the result of a violent star collision, resulting in a cloud of gas and dust from which Halla might have formed. Both explanations seem equally likely. However, the researchers emphasized that the study's crucial takeaway is that exoplanets might exist in places previously thought impossible.