In Brief
Researchers have developed a model to understand how TRAPPIST-1's seven planets manage to avoid colliding with one another. They learned that the system follows a chain of resonances at a scale never before seen in a planetary system.

Orbital Progression

February’s discovery of the seven Earth-like planets orbiting a dwarf star known as TRAPPIST-1 generated a great deal of excitement as the system seemed like a potential host for extraterrestrial life. However, further research revealed that the TRAPPIST planets seemed to be following an orbital path for destruction.

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“[I]n the original paper [when] they tried to simulate the system, planets would start colliding after a short time (astronomically speaking, about a million years),” astrophysicist Dan Tamayo told Futurism via email. However, he and colleagues from the University of Toronto Scarborough may have found a way to explain how the TRAPPIST planets survive.

In a paper published in the Astrophysical Journal Letters, the researchers explain that the mechanism that would lead to the TRAPPIST planets colliding with one another is the same one that keeps them stable — their orbit. “[I]n TRAPPIST-1, for every 2 orbits of the outermost planet, the next one in does 3 orbits, the next one 4…, 6, 9, 15, and 24,” Tamayo explained. “This is called a chain of resonances, and this is the longest one that has ever been discovered in a planetary system.”

Harmonies in Space

One can liken the chain of resonances in the TRAPPIST system to how an orchestra works. The instruments create harmonious music by keeping time with one another and making sure each one is tuned to the rest.

“Most planetary systems are like bands of amateur musicians playing their parts at different speeds,” said Matt Russo, from the Canadian Institute for Theoretical Astrophysics (CITA), who took the lead in developing an animation to demonstrate this phenomenon. “TRAPPIST-1 is different; it’s a super-group with all seven members synchronizing their parts in nearly perfect time.” He added, “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.”

Using computer simulations, the researchers modeled how the TRAPPIST system was formed and how the harmonies were finely tuned to create this unprecedented stable chain of resonances.

Certainly, this research has larger implications in our search for systems that could potentially host extraterrestrial life. While these resonances are rare in systems with massive stars like the Sun, they could be a common occurrence around smaller stars like TRAPPIST-1. “It may be that the formation conditions around low mass stars are gentler and better able to form harmonious, long lived planetary systems,” said Tamayo.

“This has implications for the prevalence of planets in the universe, since there are many small stars for every big one,” he concluded. “The exciting part is that this will be tested by upcoming missions like the Transiting Exoplanet Survey Satellite (TESS) launching next year.”