The TRAPPIST-1 Star System Is Like a Really Tight Jam Band
published during a full moon.


Back in February, NASA revealed its discovery of TRAPPIST-1, a system 40 light years away harboring seven Earth-sized planets, three of which exist in the potentially habitable “Goldilocks” zone. The momentous discovery raised far more questions than it answered, including the mystery of how the system has remained intact given that simulations of the system suggest “the planets [would] start crashing into one another in less than a million years,” according to University of Toronto Scarborough researcher Dan Tamayo. Unless researchers were incredibly lucky to find TRAPPIST-1 before its destruction, something else accounts for the system’s continued existence.

Researchers believe the stability of TRAPPIST-1 is achieved by a “resonant chain,” or a relationship between the planets’ orbits.  Orbital resonance refers to the influence planets’ gravities have on other planets’ orbits, locking them into harmony. The orbital periods of planets in a resonant configuration have a mathematical relationship based on ratios. For example, Ganymede, Europa, and Io, three Jovian moons, have a 1:2:4 resonant ratio—for each trip Ganymede makes around Jupiter, Europa makes two trips and Io makes four. Pluto and Neptune have a 2:3 resonant ratio—Pluto orbits the sun twice in the same time it takes Neptune to make three revolutions.


Orbital resonance of Jupiter and moons. Credit: WolfmanSF

This interplanetary harmony not only keeps planets, moons, and entire systems stable but accounts for their survival. Because the orbits of these bodies intersect, these objects would crash into each other eventually if their patterns were arbitrary or not in sync. Researchers have never seen this concept on the scale demonstrated by TRAPPIST-1, where the orbits of all seven planets are locked in resonance.

Researchers depict the relationship between the TRAPPIST planets in animation and sound. The underlying mathematics of the system lend itself to music, as seen in the below video in which a piano note plays every time a planet traverses its sun and a drum beat sounds when a planet passes another planet. The resulting pattern makes a song.

Canadian Institute for Theoretical Astrophysics post-doc Matt Russo explains the comparison: “Most planetary systems are like bands of amateur musicians playing their parts at different speeds. TRAPPIST-1 is different; it’s a super-group with all seven members synchronizing their parts in nearly perfect time.”

The researchers believe the planets naturally assembled into this configuration soon after they were formed. “This means that early on, each planet’s orbit was tuned to make it harmonious with its neighbors, in the same way that instruments are tuned by a band before it begins to play,” says Russo.