Planetary Harmony Keeps The Trappist-1 System Intact

Artist impression shows the seven planets orbiting TRAPPIST-1. NASA-JPL/Caltech

The seven-planet system known as Trappist-1 is a marvel of the universe. Seven Earth-size planets orbit a red dwarf just 40 light-years away. And astronomers have now confirmed how the system remains so stable.

In a paper published in the Astrophysical Journal Letter, Canadian researchers have created a detailed simulation for how the system came to be and how it survived. The planets form a “resonant chain”, which means their orbital periods are integer multiples of each other, which strongly stabilizes a system. When the planets formed they moved inward, closer towards the star, and acquired this precise configuration.

“There’s a rhythmic repeating pattern that ensures the system remains stable over a long period of time,” said co-author Matt Russo, from the Canadian Institute for Theoretical Astrophysics (CITA), in a statement.

Astronomers have suspected a resonant chain was the likely explanation but the data could not absolutely confirm this. However, the researchers put together a simulation and the resonant chain was the only scenario where the system was stable for longer than 1 million years.

“This may seem like a long time but it’s really just an astronomical blink of an eye," said lead author Dan Tamayo, at the University of Toronto Scarborough. "It would be very lucky for us to discover TRAPPIST-1 right before it fell apart, so there must be a reason why it remains stable.”

But the researchers did more than just a simulation. They also worked out a very nice way to express this resonant chain. They turned the repeating pattern into music, that you can check out in the video below. A piano note is played for every full orbit and a drum beat is played every time a planet passes its neighbors.

"Most planetary systems are like bands of amateur musicians playing their parts at different speeds,” explained Russo. “TRAPPIST-1 is different; it’s a super-group with all seven members synchronizing their parts in nearly perfect time."

There is definitely more to learn about this system. The simulation requires that the orbital alignments, just like the orbital periods, to be very precise. Otherwise, Trappist-1 would have lost its planets a long time ago.

“It's not that the system is doomed, it’s that stable configurations are very exact,” Russo said. “We can't measure all the orbital parameters well enough at the moment, so the simulated systems kept resulting in collisions because the setups weren’t precise.”

By having a simulation that looked at how the planets formed, the researchers were able to form stable scenarios. Trappist-1 has three of its seven planets firmly in the habitable zone and they are intriguing targets for life beyond the Solar System.


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