Thread by @astrotweeps

And now, thread 2/2: How the TRAPPIST-1 planets make music to save themselves from destruction!

Remember how TRAPPIST-1 shares much in common with Jupiter? There's more. Moons Io, Europa, Ganymede are locked in a 'resonant chain'.

For every orbit of Ganymede, Europa does 2 and Io does 4, so they keep ticking out a regular, repeating pattern.

Here's the most remarkable thing about TRAPPIST-1 (that didn't get much attention!): TRAPPIST-1 is a 7 planet resonant chain. Unprecedented.

Before becoming an astrophysicist, I did a degree in Jazz guitar, and this pattern of low integer ratios (3:2, 4:3..) looked familiar.

Not only is this pattern rhythmic, low integer ratios are the secret behind musical harmony. See bit.ly/2xPkQHk by @alexanderchen

So TRAPPIST-1 could be converted into rhythms and notes, and unlike every other system, it would sound musical, possibly even human.

So I scaled their orbital frequencies into the human hearing range (setting TRAPPIST-1h to a 'C') and it produced a lovely Cmaj9-type chord.

Then we used @hannorein's beautiful REBOUND code, with @astrodantamayo's own sophisticated numerical sims to play a note once per orbit.

And the result is 'TRAPPIST Sounds'

I typically get 1/2 reactions to this, the first (overused but still gold):

and the second (notice my fresh thumbs down):

And I did tell @nytimes in the most sophisticated way possible: “You can tell something is a bit twisted, the notes are a little wonky.”

Here's what's going on: TRAPPIST-1 was literally tuned into this stable resonant chain while the planets migrated through their birth disk..

...it's since had about 7 billion yrs to be slowly detuned by tidal forces. So the period ratios aren't *exactly* low integer ratios anymore

What's up with the drums? We played a drum for each 'conjunction', when the planets really communicate with each other gravitationally.

And the crackle at the end? I sped up a loop of the star's light curve (using same time scalings as for the planets), a direct sonification.

But I'm saving the best for last. There was a puzzle. When astronomers first tried to simulate the system, something like this happened:

As I started looking into the music of TRAPPIST-1, @astrodantamayo was finishing a paper that solves this mystery (in the office next door!)

He showed that if you simulate their formation into resonance while in their birth disk, the other orbital parameters are tuned too...

...and it's this fine tuning (of periods, eccentricities, inclinations, orientations) that lets the system stay stable for long time scales.