When NASA announced its discovery of the TRAPPIST-1 system back in February 2017 it caused quite a stir, and with good reason. Three of its seven Earth-sized planets lay in the star’s habitable zone, meaning they may harbour suitable conditions for life.

But one of the major puzzles from the original research describing the system was that it seemed to be unstable. “If you simulate the system, the planets start crashing into one another in less than a million years”, says Dan Tamayo, a postdoc at U of T Scarborough’s Centre for Planetary Science.

Tamayo and his colleagues seem to have found a reason why. In research published in the journal Astrophysical Journal Letters, they describe the planets in the TRAPPIST-1 system as being in something called a “resonant chain” that can strongly stabilize the system. In resonant configurations, planets’ orbital periods form ratios of whole numbers. It’s a very technical principle, but a good example is how Neptune orbits the Sun three times in the amount of time it takes Pluto to orbit twice. Since the two planets’ orbits intersect, if things were random they would collide, but because of resonance, the locations of the planets relative to one another keeps repeating.

“There’s a rhythmic repeating pattern that ensures the system remains stable over a long period of time,” says Matt Russo, a post-doc at the Canadian Institute for Theoretical Astrophysics (CITA) who has been working on creative ways to visualize the system. TRAPPIST-1 takes this principle to a whole other level with all seven planets being in a chain of resonances. To illustrate this remarkable configuration, Tamayo, Russo and colleague Andrew Santaguida created an animation in which the planets play a piano note every time they pass in front of their host star, and a drum beat every time a planet overtakes its nearest neighbour. Because the planets’ periods are simple ratios of each other, their motion creates a steady repeating pattern that is similar to how we play music. (1)

Huge planets orbiting one another.

Matter in harmony inside a vast cold space.

And in this vastness, life.

Born from the silence, noise.

The forest is not empty any more.

The forest is full of music.

Heard by beings who are meant to do more than hearing.

Pythagoras was right.

There is music in the world.

But music not made of notes.

It is music made of silence.