The Harmony That Keeps Trappist-1’s 7 Earth-size Worlds From Colliding

May 11, 2017

By Kenneth Chang

In February, astronomers announced the discovery of a nearby star with seven Earth-size planets, and at least some of the planets seemed to be in a zone that could provide cozy conditions for life.

The finding of these planets circling the star Trappist-1 40 light-years away came with a bit of mystery. The orbits of the planets are packed tightly, and computer calculations by the discoverers suggested that the gravitational jostling would send the planets colliding with each other or flying apart, some to deep space, others spiraling into the star and destruction.

Now new research provides an explanation for the dynamics of how this planetary system could have formed and remained in stable harmony over billions of years.

“It’s actually a very special system,” said Daniel Tamayo, a postdoctoral researcher at the University of Toronto Scarborough and the lead author of a paper appearing in The Astrophysical Journal Letters.

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One comment on “The Harmony That Keeps Trappist-1’s 7 Earth-size Worlds From Colliding”

  • @OP – link – The original discoverers noted that those orbits were almost exactly in what scientists call “resonance.”
    That is, the second planet completes five orbits in almost exactly the time the first planet makes eight.
    The third planet completes three orbits for every five orbits of the second planet, and the fourth planet makes two orbits for every three orbits of the third.
    The other planets are also in resonance. (In our solar system, Pluto is in resonance with Neptune, with Pluto making two orbits for every three of Neptune.)

    Orbital “resonance” from gravitational interactions is what stabilises orbits, spacing out planets or moons, by synchronising their orbital periods. If small forces tend to move them to different orbits, their passing orbiting neighbour’s gravity, pulls them back.

    Instead of just looking at the orbits of the planets today,
    they looked at possible ways that the planets got to where they are now.
    The planets formed out of a disk of gas and dust.
    After that formation, the remaining disk would have nudged the planets inward,
    and those nudges tend to push the planets toward the stable resonances.

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