In the silent expanse of space, where the vacuum reigns supreme, the notion of sound is both fascinating and elusive. Astronauts, while conducting operations, communicate with mission control through a cacophony of sounds: their breathing, the hum of their spacesuits, and the rhythmic pumping of oxygen. Yet, should they remove their helmets, all would fall silent, as sound cannot traverse the void of space.
Astrophysicist Neil DeGrasse Tyson, speaking on the podcast StarTalk, noted that in such silence, astronauts might hear the internal symphony of their own bodies, like the steady beat of their hearts.
“The sound of silence is the sound of things that were always making noise that you never noticed before,”
he explained, highlighting the unique nature of sound perception in space.
The Science of Sound in Space
Sound waves are essentially vibrations that travel through a medium such as air, water, or even the human body. These vibrations are detected by our ears and interpreted by the brain as sound. However, in the vastness of space, which is predominantly a vacuum, there are virtually no particles to carry these vibrations. Interplanetary space is sparse, with only a few dozen particles per cubic centimeter, compared to the tens of quintillions of molecules per cubic centimeter in Earth’s atmosphere.
Chris Impey, an astronomer at the University of Arizona, explains that while an absolute vacuum is rare in the universe, most of it consists of low-density, high-temperature plasma.
“In principle, sound could travel through that, but it would have very different properties to what we are used to,”
he said.
Sound Waves in the Cosmic Symphony
Despite the challenges, sound can still manifest in space under certain conditions. Gas clouds, dust clouds, and solar winds can carry sound waves, albeit in forms undetectable by the human ear. Phil Plait, an astronomer known for The Bad Astronomy blog, notes that the structures of many gas clouds are shaped by sound waves or shock waves when material moves faster than sound.
“We see the effects of sound in these objects all the time,”
Plait remarked.
In 2003, NASA detected pressure waves emanating from a black hole in the Perseus galaxy cluster, 250 million light-years away. These were not traditional sound recordings but pressure waves converted into sound, corresponding to a B-flat note, 57 octaves below middle C on a piano. In 2022, NASA’s Chandra X-ray Observatory further sonified this data into audible frequencies, demonstrating the potential for sound to reveal cosmic phenomena.
Sound Beyond Earth: Mars, Venus, and Titan
Sound detection is not limited to distant galaxies. Within our solar system, NASA’s Perseverance rover on Mars captured sounds of Martian winds and the whir of its helicopter in 2021. Similarly, the Soviet Venera 13 mission in 1981 reported sounds on Venus, akin to waves hissing on a beach.
Tim Leighton, an acoustics professor at the University of Southampton, has modeled how sound behaves on other planets. On Mars, the atmosphere is only 2% as dense as Earth’s, dominated by carbon dioxide, leading to quieter and muffled sounds. Interestingly, a church organ’s flue pipes would pitch up, while reed pipes would pitch down.
Saturn’s moon Titan offers an acoustic environment closest to Earth, though with higher pressure and density, affecting sound pitch. On Venus, the dense atmosphere results in a unique auditory experience where solid object vibrations pitch down, while air-propagated sounds pitch higher due to the planet’s extreme heat.
Exploring Planetary Acoustics
Recording sound on other planets can provide insights into their atmospheres and geological processes. For instance, analyzing wind sounds on Mars could reveal how its surface evolves. Leighton emphasizes the potential of microphones in planetary exploration, stating,
“It can tell us a lot about the atmosphere and how it changes as the sun goes up and down, and how that, in turn, generates winds to shape the surface of Mars.”
Sound could also aid in exploring planets like Jupiter and Saturn, where thick clouds obscure visual observation. Impey suggests that sound might offer a more efficient way to sense planetary conditions than cameras, which struggle in such environments.
The Cosmic Echoes of the Early Universe
Astronomers have even ventured to capture the sounds of the early universe. The universe’s first million years were a dense plasma soup, carrying acoustic oscillations. Astronomer Mark Whittle compressed this cosmic history into a 10-second audio clip, shifting it up by 50 octaves to make it audible. He described it as
“a descending scream, a deep roar and a final growing hiss.”
These early sound waves, known as Baryon acoustic oscillations, influenced the distribution of galaxies and, by extension, the formation of life on Earth. As Whittle eloquently put it,
“Within that sea of brilliance, the seeds for all that we now know were already present, latent, waiting to unfold.”
In the grand scheme of the cosmos, sound plays a subtle yet profound role, offering a unique lens through which we can explore and understand the universe. As we continue to push the boundaries of exploration, the silent symphony of space may yet reveal more of its secrets.
