Locked in a Dance

NASA's Kepler mission has revealed that many planets in our universe could be candidates for harboring life. We have seen planets that inhabit the habitable zones of their star systems, and examples of planets that mimic many of Earth's qualities. But while its main mission is to find alien worlds that could possibly support life, it has also revealed systems with strange and quirky properties.

Speaking of strange, a team of astronomers have recently found a star system where four gas giants have been locked in a resonance for more than 6 billion years. It means that for that whole period of time, their orbital periods have been related to each other in small-integer ratios.

In layman's terms, resonance means that in a hypothetical system, when one planet orbits the star once, the other has gone around twice.

For the system Kepler-223, four planets, Kepler-223 b, c, d, and e, have been locked in this resonance. Kepler-223 b and c – the system’s two innermost planets – are in a 4:3 resonance. Kepler-223 c and d are in a 3:2 resonance. And Kepler-223 d and e are in a 4:3 resonance.


Astronomers have found systems with two or three planets in resonance, but four planets is a first.

To find the system, the astronomers first determined the precise size of the star. Then they used brightness data from the Kepler telescope to analyze how the four planets block the starlight and change each other’s orbits, thus inferring the planets’ sizes and masses.

All of this was for the precise goal of finding out exactly how and where planets form. It is hypothesized that most solar systems start out with planets with resonances, but asteroids and small planets knock them out of resonance as time passes by.

It is theorized that this happened to Jupiter, Saturn, Uranus, and Neptune—being knocked out of resonances that mirror that of Kepler-223.


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