Astronomers discover giant planet orbiting a star that should have destroyed it

Astronomers using NASA's Transiting Exoplanet Survey Satellite (TESS) recently discovered a massive planet orbiting a red giant star that should have destroyed it.

The planet, 8 Ursae Minoris b, orbits a star some 530 light years away from Earth. The star would have been expected to expand beyond the planet's orbit before receding to its present (still giant) size, engulfing and ripping apart any planets orbiting closely around it. But the gaseous planet somehow continues to exist in a stable, nearly circular orbit. 

Astronomer Marc Hon of the University of Hawaii, the lead author of a recent paper on the discovery, proposes two possibilities - either planet is really the survivor of a merger between two stars or it’s a new planet formed out of the debris left behind by that merger.

Explaining how astronomers infer such a chaotic series of events from present-day observations, Pat Brennan, NASA's Exoplanet Exploration Program, stated, "It all comes down to well-understood stellar physics. Planet-hunting TESS also can be used to observe the jitters and quakes on distant stars, and these follow known patterns during the red-giant phase. (Tracking such oscillations in stars is known as asteroseismology) The pattern of oscillations on 8 Ursae Minoris, the discovery team found, match those of red giants at a late, helium-burning stage – not one that is still expanding as it burns hydrogen. So it isn’t that the star is still growing and hasn’t yet reached the planet. The crisis has come and gone, but the planet somehow continues to exist."

Discovery Alert! 📣 Planet 8 Ursae Minoris b, also known as Halla, orbits a star 530 light-years away in its death throes. The red giant star would have been expected to engulf and rip apart any close planets. Yet Halla remains. https://t.co/Q4tY87XHOe pic.twitter.com/sXN6hGlAib

— NASA Exoplanets (@NASAExoplanets) September 20, 2023