We periodically get to share news stories about solar systems where planets or moons orbit in cool rhythms. In our own solar system, the Galilean moons of Jupiter have their own syncopated beat, with Ganymede taking the bass line and orbiting once for every two Europa orbits and four Io orbits. 

This kind of a rhythm occurs all over space, and one particular system, HR 8799, recently caught the attention of researchers Dimitri Veras and Sasha Hinkley who decided to see what will happen as this system’s central star evolves. As it stands, the system’s four worlds orbit in an 8 to 4 to 2 to 1 resonance, but as the system’s bright, hot, A-type star loses mass, those orbits will expand, and the planets, all larger than Jupiter, will violently interact as they drift a bit too close together and gravitationally fling one another around like planetary nunchucks. 

The details of what will go down weren’t actually possible because changing planetary positions by even a centimeter at the beginning of the model would lead to massive differences at the end of the model, and if those worlds have moons, their actual positions may wander significantly more than a centimeter!

According to Veras, the planets are so big and so close to each other the only thing that’s keeping them in this perfect rhythm right now is the locations of their orbits. All four are connected in this chain. As soon as the star loses mass their locations will deviate, then two of them will scatter off one another, causing a chain reaction amongst all four.

I have to admit, I now really want a Star Trek episode or something about a star system ending this way. Science fiction writers, you have your prompt!

More Information

Warwick University press release

“The post-main-sequence fate of the HR 8799 planetary system,” Dimitri Veras and Sasha Hinkley, 2021 May 14, Monthly Notices of the Royal Astronomical Society