Over one hundred years ago British composer Gustav Holst debuted an orchestral masterpiece in which the planets were each represented by a piece of classical music. Since its introduction in 1918 Holst’s The Planets has acted as a romantic soundtrack to our solar system. 

We now know the universe is a lot quieter than Holst imagined. But the planets do each sing a unique song.

Sci-Fi soundtrack: The first piece in Holst’s The Planets, Mars, Bringer of War, inspired musical scores in science fiction movies such as Star Wars!

Here on Earth, we are used to our days and nights being filled with sounds of all kinds.

Sound waves travel from one point to another through molecules bumping into other molecules. Once they reach an ear, they bounce against the eardrum causing a vibration that passes through the tiny bones in the ear and make small hairs within vibrate. Those hairs convert the vibrations into electrical signals that travel through nerves to the brain where they are translated into qualities of sound: loudness, pitch and timbre.

A sound will travel outward from its source like the ripples that spread out across a pond when a stone is dropped into it. Like those ripples, sound diminishes the farther away it gets from its origin.

On Earth, molecules are plentiful and help deliver sound to our ears. In space, however, there are very few molecules to help carry sound and the molecules that are there are too far apart to bump into one another. 

So, while there are vibrations in space, there are no molecules to carry them to an ear that might interpret them. If you were to call to a person standing next to you the sound would not travel away from your mouth. They could see you calling to them but not hear what you were saying.

How do we hear a planet?

Each planet emits radiation of some sort but the signals from these charged particles are not carried on sound waves. Using satellites and telescopes, scientists are able to measure and collect information about these emissions which is then sent back to Earth.  That data is then fed into a computer and translated into sound waves which when played back allow you to ‘hear’ the planet.

Spooky sounds: In the 1990s NASA captured and processed emissions from the planets in a collection of spooky space sounds.

Dig that groovy data: The music we listen to over computers and phones is simply data that has been sent and reassembled into sound waves for us to enjoy.

The sounds produced in this way may not be what the planet actually sounds like, but they are an interpretation of them. By turning the data from each planet into something we can hear we can enjoy the universe with more than our eyes.

Martian melody: When Perseverance landed on Mars earlier this year it was able to record the sound of the wind blowing across the surface of the planet.

Article originally published in Brainspace Magazine Winter 2021/2022