Last year, the Perseverance rover of NASA (the National Aeronautics and Space Administration of the US) recorded the first audio from Mars, giving us a glimpse for the first time of how the Red Planet actually sounds.

The soft winds, blowing at 5mph, seem like a soothing lullaby, coming from a barren planet that's inspired our imagination for millennia.

And while the James Webb Space Telescope unveils new regions of the observable universe thanks to the highest-resolution images we’ve ever seen, scientists also focus their attention on the sonic properties of space.

And never mind that sound waves can’t travel through space, as humans today can recreate the sound of objects millions of light years away.

Human interest in sounds from the universe dates back to the early years of space travel.

Think of the Venera 14, the Russian probe that recorded sounds from Venus in 1982 before being crushed by the incredible air pressure and heat of our neighbour’s surface.

Or the sounds made by the plasma waves around Earth, recorded in incredible detail by the Van Allen Probes.

The sound of planets and space objects can tell us a lot about their properties but also ignite the imagination of the Earthlings fascinated by space.

And while our rovers and probes carry acoustic microphones to capture the sounds of planets, scientists use the latest technologies to explore the soundscapes of places we’ve never been before.

HOW SPACE SOUNDS ARE COLLECTED

OSIRIS image of Mars taken during voyage of ESA Rosetta spacecraft, Credit ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA / Wikimedia Commons

Essentially, there are two ways for humans to listen to sounds from space.

The first and most straightforward one is by capturing audio on other planets using the built-in microphones on the space rovers roaming the surface.

The Perseverance rover was able to capture the sounds of Martian gusts of wind thanks to two microphones: one is part of the SuperCam instrument and, among other tasks, listens to the sounds of lasers hitting distant rocks to help determine their hardness and mass.

The other microphone’s mission was to record audio from the rover’s entry, descent, and landing on Mars.

While it failed to record the turbulent winds from the rover's touchdown, it’s been capturing other sounds from the Red Planet for the last year and a half.

While Mars, like Earth, has an atmosphere that allows sounds to travel freely on its surface, the atmosphere’s composition is so different from the one on our planet that it has a significant impact on how sound works there.

The difference in the atmosphere’s temperature, chemical composition, and density make Mars the perfect scientific playground to explore how sound might travel on other planets.

This then leads to an important question. How do we know what distant planets, stars and other space objects sound like?

Sound waves require a medium to travel from their source to our ears, like air or water. The vastness of space is almost empty, which means that even if we had space probes travelling through the cosmos, they wouldn’t be able to capture audible frequencies with standard microphones.

THE DATA SONIFICATION OF SPACE SOUNDS

This is when data sonification comes into play. But before we delve into this fantastic technology, let me explain what sound is.

Sound waves are called as such because they're a vibration that transfers energy through a medium, like air.

So the sound you hear is the result of the particles of the medium being affected by the vibration from the source. Eventually, particles lose energy, and the sound dies out.

If there’s no medium, we can’t hear any sounds.

However, the vibration of the source is still there, and so are many other waves that can travel in space without a medium and tell us a lot about how an otherworldly object might sound.

Space is full of plasma waves, radio waves, magnetic waves, gravitational waves and shock waves, which can be recorded by instruments that can sense them, and the data transferred to Earth, where the waves are sound-coded.

For instance, electromagnetic waves and sound waves pulsate at the same wavelength, meaning we can use them to turn non-acoustic data into audible sounds by converting the electromagnetic wave into a sound wave and bringing it up to the range of human hearing.

These sounds are the oscillating electric and magnetic fields detected and played back as audio, and similar results can be obtained electronically with all the data we receive from space in the form of wavelength, often resulting in eerie sounds that make you wonder why we should venture out in space, after all.

However, data sonification can also be used to combine beautiful, cinematic sound effects with images from space telescopes.

This combination of science and creativity often brings to life immersive works of art, with soundscapes that aim to represent space pictures using synth effects, strings, or simply piano.

To get an idea of how this process works, check out the “System Sounds” project by M Russo and A Santaguida.

OTHER OTHERWORDLY SPACE SOUNDS

NASA Solar and Heliospheric Observatory (SOHO) spacecraft, Credit: Cgruda/Wikimedia Commons

In 2018, the ESA (European Space Agency) published the sound of the Sun, or rather, the perpetual movement of the sun’s atmosphere transformed into audible frequencies.

To achieve this remarkable result, the Solar and Heliospheric Observatory (SOHO) recorded the sun’s movements for forty days, and the data was then processed and sonified by Alexander Kosovichev, the director of the Big Bear Solar Observatory.

Now, what about the sound of a comet?

For years, scientists have been using the Rosetta Plasma Consortium (RPC) magnetometer to measure sound wave vibrations in the comets’ magnetic field. Through data sonification, they’ve been able to translate magnetic-field data into sounds and share cosmic audio with the rest of the world.

The most famous and fascinating example of a comet’s sound is undoubtedly the case of comet 67P/C-G.

First heard in 2014, 67P/C-G “sings” in a unique way and left scientists puzzled for years as to why the magnetic-field sound waves of this apparently ordinary comet were so different from all the other comets.

It turned out that this unique sound is caused by a stream of plasma articles that leave the comet’s surface and interact with its magnetic field.

A few days ago, Nasa released sounds coming out of a black hole in the Perseus galaxy cluster.

The cluster is immersed in hot gas, which can act as a medium for the black hole’s sound: these acoustic waves can then be translated into audible frequencies.

Scientists were also able to identify the note the back hole is “playing” on: it’s B-flat, 57 octaves below middle C.

So you might want to tune down your guitar before you start jamming with a black hole!

This is the lowest note ever recorded in human history: with a pitch whose frequency is ten million years, NASA had to transpose it 57 octaves up in order for us to hear it.

As NASA stated when they first released the sound of a black hole, the idea that there’s no sound in space is a misconception.

We’re at the beginning of our sonic exploration of space, but the discoveries so far lead us to believe that in space, there's much more than the human ear can hear.

Cover Credit: Ardea-Studio/Shutterstock, Dotted Yeti/Shutterstock, Cottonbro/Shutterstock, Luz Calor Som/Pexels

Writer | Marco Sebastiano Alessi

Marco is an Italian music producer, composer and writer. He’s the founder of Naviar Records, a music community and record label exploring the connection between experimental electronic music and traditional Japanese poetry.

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