Stephanie G. Mathis The planets orbit their star parents while being separated by vast distances. In our solar system, the planets are similar to grains spread over a region as large as a football pitch. The time it takes planets to orbit their suns has no relationship with each other.
Harmony of the spheres
Pythagoras, a Greek mathematician, discovered musical harmony by analysing the sounds of blacksmiths’ hammers and strings plucked 2,500 years before.
He thought mathematics was the foundation of nature and suggested that the Sun and Moon emit unique hums depending on their orbital properties. He believed that this “music of spheres” was imperceptible by the human ear.
This idea was first conceived by Johannes Kepler 400 years ago. He suggested that musical intervals, harmonies, and movements of the six planets known at the time could be described by the music.
Kepler believed that the solar system consisted of four voices: two basses (Jupiter and Saturn), a tenor (Mars), two altos (Venus and Earth), and one soprano Mercury. The roles were based on the speed at which each planet orbited the Sun. For the outer planets, the speeds are slower and for the inner ones higher.
Although these ideas are similar to the concept of orbital resonation, planets do not actually make sound, because sound cannot travel through the vacuum of outer space.
Orbital Resonance
Resonance occurs when planets and moons have orbital period ratios that are whole numbers. The orbital period is how long it takes for a planet or moon to complete a full circuit around a star. Two planets orbiting the same star, for instance, would be in 2:1 resonance if one planet took twice as long to orbit the star as the other. Only 5% of planetary systems show resonance.
Orbital resonance occurs when the orbits of planetary bodies line up. For example, Io orbits Jupiter 4 times faster than it takes Europa and Ganymede each to orbit Jupiter twice. WolfmanSF/Wikimedia Commons
Neptune is in a 3 to 2 resonance with Pluto. A triple resonant is also present between Jupiter’s three satellites, Ganymede and Europa. Io and Europa orbit Jupiter four times in the time that it takes Ganymede. When planets have orbital periods, which are ratios of whole numbers, resonances can occur.
Musical intervals are the relationships between two notes. The fourth, 4 to 3, the fifth, 3:1, and the octave are important intervals that can be derived from ratios of frequency. These intervals will be familiar to anyone who has played the piano or guitar.
Scales and harmony can be created using musical intervals.
Orbital resonances change the way gravity affects two objects, causing their orbits to accelerate, slow down or stabilize.
Imagine pushing a kid on a swing. Both a planet and a child’s swing have a similar natural frequency. You can give the child a boost by pushing them in the same motion as the swing. You can also give them a boost by pushing them every second time or even every third time. Push them randomly, sometimes in the direction of the swing and sometimes against it, and you won’t get a boost.
Planets and asteroids can be accelerated or wobbled by orbital resonance.
The boost to planets can help them maintain their orbital path, but is more likely than not to cause their orbits.
Exoplanet resonance
Exoplanets or planets that are outside of the solar system show a striking example of resonance. Not only between two objects, but also in “chains” consisting of three or more objects.
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The star Gliese 876 has three planets with orbit period ratios of 4:2:1, just like Jupiter’s three moons. Kepler 223 has four planets with ratios of 8:6:4:3.
The red dwarf Kepler80 has 5 planets in ratios 9:6;4:3:2, while TOI178 contains 6 planets. Five of them are in a resonant sequence with ratios 18:9;6:4.
TRAPPIST-1 holds the record. It has seven Earthlike planets. Two of them could be habitable. The orbit ratios are 24:15:9;6:4:3;2.
The HD 1110067 is the newest example. The system is about 100 light-years away, and it has six subNeptune exoplanets. This discovery is significant because most resonance chains disappear with time.
Only 1% of planetary systems show resonant chain. Astronomers believe that planets are formed in resonance. However, small gravitational nudges by passing stars or wandering planets can erase this resonance over time. HD 110067 is a rare example of a resonant system that has survived billions of years. It offers pristine views of the system at its formation.
Orbit sonification
Astronomers translate complex visual data using a technique known as sonification. This technique allows people to enjoy the stunning images of the Hubble Space Telescope in a new way. It has also been used to translate gravitational wave data.
Sonification is a way to convey mathematical relationships between exoplanets and their orbits. The European Southern Observatory has created “Music of the Spheres” for the TOI 178 System by assigning a sound to each planet on a pentatonic system.
The European Southern Observatory has created music based on the orbits of planets.
The TRAPPIST-1 system has a similar musical translation, but the orbital frequency scaled up to a factor of 212,000,000.
