Astronomers have finally confirmed how the TRAPPIST-1 system manages to survive. Its seven Earth-sized planets orbit the star in a perfectly synchronized fashion.

In scientific terms, the planets are in orbital resonance. Their periods around TRAPPIST-1 are in proportions that guarantee their gravitational pulls don't send any of the planets into stars or fling them out. This orbital resonance has been suspected since the discovery of the planets months ago, but only now have astronomers gathered enough information on the seventh planet, TRAPPIST-1h, to confirm it. The results are published in Nature Astronomy.

"It really pleased me that TRAPPIST-1h was exactly where our team predicted it to be. It had me worried for a while that we were seeing what we wanted to see – after all, things are almost never exactly what you expect them to be in this field," lead author Rodrigo Luger, a doctoral student at UW, said in a statement. "Nature usually surprises us at every turn, but, in this case, theory and observation matched perfectly."

The team's theoretical work focused on data from the first six planets. By using their precise distance, orbital periods, and velocities, they were able to constrain what TRAPPIST-1h could be doing. They found that planet h had only six possible orbital periods allowed if the star system was indeed in orbital resonance. The data showed them the correct one.

Once knowing that this relationship between the planets exists, it becomes crucial to understand how it came to be. Astronomers believe that the orbital resonance happened as the planets moved towards the star when the system was still very young.

“All of this indicates that these orbital relationships were forged early in the life of the TRAPPIST-1 system, during the planet formation process," Luger said.

"The resonant structure is no coincidence and points to an interesting dynamical history in which the planets likely migrated inward in lock-step, added Luger. "This makes the system a great laboratory for planet formation and migration theories."

The discovery was possible thanks to a large collaboration of scientists from around the world. The researchers used social media to discuss the data in real time, as soon as the K2 mission released it.

"Pulling results out of data is always stimulating, but it was a rare treat to watch scientists across the world collaborate and share their progress in near-real time on social media as they analyzed the data and identified the transits of TRAPPIST-1h," added Jessie Dotson, project scientist for the K2 mission at NASA's Ames Research Center.

TRAPPIST-1 is located less than 40 light-years away and three of its planets are in the habitable zone. The system is a prime candidate for life beyond the Solar System.