Announced at last week’s AAS press conferences was the discovery of three planets that are teetering on the brink of destruction because they are orbiting dangerously close to their parent stars. One of these planets, TOI-2337b, has less than a million years to survive, making it the most endangered known planet.

The threatened planets were found in NASA TESS image data from 2018 and 2019. Follow-up observations were performed using a spectrometer at the Keck Observatory in Hawai’i to confirm the planets.

In a paper accepted to The Astronomical Journal, researchers presented detailed estimates of the planets’ masses and sizes, with mass ranges of 0.5 to 1.7 times Jupiter’s mass and size ranges from just less than Jupiter’s size to 1.6 times its size. Basically, a bunch of Jupiters, really. Gas giants everywhere!

Densities for the planets range from styrofoam-like to about three times as dense as water, which means these planets have different origin stories across the board. That’s pretty cool and kind of frustrating because it adds more complexity to our planetary formation hypotheses. Honestly, there may be too many variables to come up with one cohesive formation theory. We’ll likely have to tailor potential outcomes based on the parent star’s age, type, how big the protoplanetary disk is, which way the winds were blowing through the gas cloud that formed the star itself. I could go on and on.

But the main objective in studying these three planets, and the potential hundreds to be found later, is to understand the end of life for a planet. Per the press release, Current models of planet dynamics suggest that planets should spiral in toward their host stars as the stars evolve over time, particularly in the last 10 percent of the star’s lifetime. This process also heats the planets, potentially causing their atmospheres to inflate. However, this stellar evolution will also cause the orbits of planets around the host star to come closer to one another, increasing the likelihood that some of them will collide, or even destabilize the entire planetary system.

Now we wait for some time on the JWST to gain some insight into what the planets’ atmospheres are made of – water, carbon dioxide, etc. That would help researchers put some constraints on the formation of these worlds and what sorts of interactions might have led them to where they are today. Planetary formation, it seems, is messy.

More Information

Keck Observatory press release

“TESS Giants Transiting Giants II: The hottest Jupiters orbiting evolved stars,” Samuel K. Grunblatt et al., to be published in The Astronomical Journal (preprint on arxiv.org)