Astronomers have spotted a planet that appears to have survived being engulfed by its sun. 

An international team including researchers from the University of Sydney has found a planet that managed to survive the destructive fate that awaits many planets as their host stars age. 

The gas giant planet, named Halla, orbits the giant star Baekdu in the Ursa Minor constellation. 

The team, led by Dr Marc Hon from the University of Hawai'i, made a remarkable find by observing Baekdu's stellar oscillations using NASA's Transiting Exoplanet Survey Satellite (TESS). 

Their findings, published in the journal Nature, reveal that Halla survived a violent stellar transition that would typically annihilate nearby planets.

“Engulfment by a star normally has catastrophic consequences for close orbiting planets,” says Dr Dan Huber, a member of the research team.

“When we realised that Halla had managed to survive in the immediate vicinity of its giant star, it was a complete surprise.” 

Baekdu, with a radius almost 11 times that of the Sun and 1.6 times its mass, had once expanded into a red giant star, a phase that usually spells doom for planets in close orbits.

The discovery of Halla was confirmed through additional observations conducted using the W. M. Keck Observatory and the Canada-France-Hawaii Telescope on Mauna Kea, Hawai‘i. 

These observations validated the planet's stable orbit and led to the intriguing question of how it managed to survive. 

The researchers propose two possible explanations: either the merger of two stars prevented Baekdu from expanding enough to engulf the planet, or Halla is a “second-generation” planet formed from the collision of the two stars.
“We just don’t think Halla could have survived being absorbed by an expanding red giant star,” Dr Huber said.

The more plausible theory for the planet’s survival could be that it never faced the danger of engulfment.

“The system was more likely similar to the famous fictional planet Tatooine from Star Wars, which orbits two suns,” said Professor Tim Bedding from the University of Sydney.

“If the Baekdu system originally consisted of two stars, their merger could have prevented any one of them from expanding sufficiently to engulf the planet.”

This discovery challenges the current understanding of exoplanets and suggests that other planets in close orbits around evolving stars may also evade destruction.