A Star With Six Planets That Orbit Perfectly in Sync

Astronomers have discovered six planets orbiting a bright star in perfect resonance. The star system, 100 light-years from Earth, was described on Wednesday in a paper published in the journal Nature. From a report: The discovery of the system could give astronomers a unique opportunity to trace the evolution of these worlds to when they first formed, and potentially offer insights into how our solar system got to be the way it is today. "It's like looking at a fossil," said Rafael Luque, an astronomer at the University of Chicago who led the study. "The orbits of the planets today are the same as they were a billion years ago." Researchers think that when planets first form, their orbits around a star are in sync. That is, the time it takes for one planet to waltz around its host star might be the same amount of time it takes for a second planet to circle exactly twice, or exactly three times. Systems that line up like this are known as orbital resonances. But, despite the theory, finding resonances in the Milky Way is rare. Only 1 percent of planetary systems still preserve this symmetry. Most of the time, planetary orbits get knocked out of sync by an event that upsets the gravitational balance of the system. That could be a close encounter with another star, the formation of a massive planet like Jupiter, or a giant impact from space on one planet that causes a ripple effect in other orbits. When this happens, Dr. Luque said, planetary orbits become too chaotic to mathematically describe, and knowledge of their evolution is indecipherable. Astronomers are lucky to find even one pair of exoplanets in resonance. But in the newly discovered star system, there are a whopping five pairs, because all six planets have orbits that are in sync with one another. Dr. Luque described it as "the 1 percent of the 1 percent."

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