These six planets have been orbiting their sun rhythmically for a billion years

With a little imagination you could call it ‘cosmic music’: six planets orbit their sun in a very precise rhythm. Every time the first planet makes three rounds, the second planet makes two. If he has made three rounds, the third has made two rounds. The planets have been circling the sun in the same rhythm for at least a billion years, almost as if they were dancing a waltz. The fixed proportion in their movement has remained the same all this time.

This was discovered with the help of the European Space Agency’s Cheops mission. The planets are located in the constellation Coma Berenices, also known as Head Hair, about a hundred light-years away from Earth. The results of the study are published in the scientific journal Nature.

This animation explains the analogy with a musical rhythm:

The planets were discovered because the luminosity of their sun, the star HD110067, occasionally decreased slightly. That is an indication that a planet is moving past this sun at that moment and is blocking the light. Further study initially showed that there were two planets, and a third planet was soon discovered.

Once the position of the first three planets was known, the researchers could predict where the remaining planets would be located simply by using the three-to-two ratio. Observations made it clear that the other three planets were indeed in the calculated location.

Scientists call this rhythmic circling of the planets ‘resonance’, a term that also occurs in music: their movement is similar to how the strings of an instrument can resonate with each other. Strings or parts thereof that are not struck resonate in their fundamental tone or one of their overtones with struck strings with the same fundamental tone or overtones.

If you were to sound the strings of a piano in the same proportion as found for these planets, you would hear a fifth: the first and fifth notes of a scale.

When solar systems are formed, planets revolve rhythmically around the sun much more often. But major events, such as impacting space rocks or planets changing position, sooner or later put an end to that regularity in 99% of all solar systems. This has also happened in our own solar system.

“That probably has to do with the formation and movement of Jupiter and Saturn,” explains lead researcher Rafael Luque. “Many scientists today assume that these two planets swapped places at some point. This likely caused a domino effect that caused the planets to lose their resonance.”

This does not mean that resonance no longer occurs in our solar system. Three of Jupiter’s four largest moons orbit the planet in a steady rhythm. If the first moon makes one circle, the next makes two, and a third makes double that: four. In musician’s terms, this resonance is not one of a fifth, but of an octave, with the frequency of the second tone being exactly double (or exactly half) that of the first.

Don’t expect life on the newly discovered planets. Even on the coolest of the six it is about 170 degrees, that’s how close they are to their sun. They can best be compared to the planet Neptune in our own solar system: a rocky core surrounded by a thick atmosphere, probably containing helium and hydrogen.