"In space, no one can hear you scream," reads the tagline for the original Alien movie. And that's true: for the most part, interplanetary space is just a big bag of nothing. But that doesn't mean it's completely silent.
Human ears are specially designed to translate changing pressures traveling through a medium (i.e. sound waves). These sound waves are rendered mute once the medium they are traveling through comes to an end (say, when the atmosphere on Earth gives way to the emptiness of space). However, there are plenty of waves that can move through a vacuum. We can then translate these vacuum-friendly waves into sounds that humans can hear (that's how things like radio transmissions work).
Over the past few decades, we've sent a number of satellites to the far reaches of the solar system (and beyond, as you'll see below). For research and communication reasons, these vessels left with sensors designed to "hear" things like radio and plasma waves that flow freely through interplanetary space. Using a technological intermediary, humans are able to "hear" these space waves as audible sounds.
Turning space waves into sounds has a scientific advantage—evolution has cultivated the human brain to be really good at discerning tiny sonic nuances. This ability helped our ancestors know a growling predator was in the area and was instrumental in developing the complexities of speech. In the days before beefy analytical software, listening to audio interpretations of space waves was one of the best ways to learn what was going on.
However, on a more visceral level, these literally alien noises have a definite effect on the human brain—they're super spooky! These audio files are just about the only ways we can appreciate what it's like to actually be in outer space. Here are eight creepy sonic experiences captured by NASA over the past few decades.
What Jupiter Sounds Like
During its historic 20-year mission to Saturn, NASA's Cassini spacecraft stopped by Jupiter to receive a gravitational boost en route to its final destination). During its fly-by in January 2001, it captured these spooky and quite alien radio signals.
What Europa Sounds Like
As the Galileo spacecraft passed by the Jovian moon Europa, it read these plasma fluctuations resulting from the interaction of Europa and Jupiter's magnetospheres.
What Ganymede Sounds Like
As Galileo passed by Jupiter's moon Ganymede, it discovered some strange plasma wave observations that confirmed Ganymede has its own magnetosphere. Translating the moon's interactions with Jupiter's more massive magnetosphere resulted in these spooky sounds.
Jupiter's 'Bow Shock'
The sun emits a steady stream of charged "solar wind," which can be repelled by a strong magnetic force—say from the magnetic field of a large planet. When the solar wind meets this strong magnetic force surrounding a planet, it is deflected and all its energy of motion is converted to thermal energy. This energized region is known as a "bow shock" (which borrows its name from a similar phenomenon in aerodynamics). The "sound" of passing through this region was recorded by the Voyager spacecraft.
What Callisto Sounds Like
The moon Callisto appears to have the weakest interaction with Jupiter's magnetosphere of any of the four largest moons.
The Sounds of a Thunderstorm on Saturn
Researchers have noted evidence of lightning deep within Saturn ever since Voyager flew by. These static-y crackles in radio waves were captured by Cassini in 2006 and show the chaotic environment simmering deep below Saturn's cloud top.
What Crossing Saturn's Ring Sounds Like
This static was recorded by Cassini's Radio and Plasma Wave Science instrument as it crossed the plane of Saturn's rings in December 2016.
Voyager Crossing Into Interstellar Space
This sound isn't a real-time recording, but rather an audio version of a graph of the Voyager's Plasma Wave Science observations of several months spanning 2012-13. These readings mark the period at which scientists believe Voyager exited our solar system's heliopause—the area in which the pressures from outside our solar system force what's left of the sun's solar wind to turn back. In effect, this is the point at which Voyager left the solar system—the first human-made object to do so.