Doomed Exoplanet TOI-2109b Spirals Toward Its Star with Three Possible Fates

The gas giant TOI-2109b is more than five times as massive as Jupiter, and resides in a perilous orbit 870 light-years from our planet. As an “ultrahot Jupiter,” it completes a lap around its parent star in a mere 16 hours, the briefest orbit of any such planet known. It is baking its atmosphere to broiling temperatures, and inching closer to oblivion in an orbit that is slowly pulling it in toward its parent sun. Using archived space telescope data from TESS and Cheops, astronomers have observed the testimony of this inevitable spiral, and contemplated three (wildly divergent) possible fates of the doomed planet.

Fates for TOI-2109b

According to the new research, conducted with data from NASA's TESS and ESA's Cheops missions shows that TOI-2109b's orbit is decaying — a process it will continue for thousands of Earth's years to come by 10 seconds over three Earth years. This proves that it is in a process of slow in fall. If the decay becomes worse, the planet may start falling directly into its host star and create a luminous flare, just like ZTF SLRN-2020. Alternatively, the star's tidal forces could permanently warp the planet and rip it asunder.

A Potential Planetary Rebirth

There is a third, less-tragic possibility which could happen through a process of photoevaporation, in which strong radiation from the hosting star removes TOI-2109b's gaseous envelope to reveal its rocky core. If the planet shrinks quickly enough, it might survive the process, avoiding its destruction by spiraling within its eternal Roche limit, and settling as a super-Earth or Neptune-sized blow-up hard relic. Then TOI-2109b would be an odd, rare opportunity to witness up close how this process unfolds.