What does space sound like?

A team at the University of Iowa are listening to the sounds of space - Izzie Clarke had an ear out...

Bill - Well, I think it sounds like a soundtrack from a Star Trek movie.

Izzie - That’s Bill Kurth. He’s a research scientist at the University of Iowa and an investigator on Cassini, Jeno and Voyager leaving the solar system…

Bill - What we’re actually listening to are radio emissions from lightning strokes after they’ve propagated into the surrounding environment around Earth, which we call it’s magnetosphere.

Izzie - A magnetosphere surrounds a planet that has a magnetic field, and within lies a cloud of charged particles. These sci-fi-esque signals, called whistlers, were detected by the Van Allen probe which - surprise, surprise - got it’s name from within a region of the Earth’s magnetosphere known as the Van allen radiation belt.

As the lightning from Earth discharges, protons and electrons smack into this radiation belt and move back and forth as they escape into space along the Earth’s magnetic fieldlines...

Bill - We’re detecting electromagnetic waves. These are like radio waves that propagate in the magnetosphere so when there are disturbances in this medium they create electromagnetic waves.

Izzie - These signals aren’t picked up as sound waves, but are electromagnetic waves given off from charged particles colliding. These can be processed at the same frequency and then converted into sound. But whilst it’s cool that we can hear particles escaping our atmosphere - we can go further…

Bill - The Voyager 1 recording of Jupiter’s bow shock is my favourite of all the recordings we’ve made in the last 40 years. It’s just exquisite.

Izzie - This bow shock all starts with solarwinds. A stream of charged particles known as a plasma from the Sun’s atmosphere soaring through space at 1 million miles per hour…

Bill - The first sounds that you hear are some fairly high squeaks and whistles. These are occurring in the solar wind which is approaching Jupiter’s magnetosphere - Jupiter’s magnetic bubble.

Izzie - Jupiter’s magnetosphere is the largest structure in our solar system. So what happens when plasma travelling at such high speed collides with this enormous astronomical obstacle?

Bill - Just like an aircraft travelling supersonically in our atmosphere, there has to be a sonic boom and, in this case, we call it a bow shock… This is where the solar wind is heated, deflected, and slowed down so that it can get round the boundary.

Izzie - So how can we hear these sonic booms in space?

Bill - Well, the Voyager instruments from the University of Iowa have a very simple antennae system. They have one electric dipole antennae; this is an antennae that has two long rods, each of the rods is 10 metres long, and we basically use them like you would use rabbit ears on a television, back when people did that sort of thing. Those antennas detect the electric fields of the waves in the plasma. The signals from the antennae are recorded in digital form on the spacecraft and then they’re played back tot the deep space network and, eventually, to our computers. We can basically take that wave form and turn it into an mp3 file and play it through an iPod or just an amplifier and a speaker. That’s how we hear these sounds.

Izzie - Now remember those whistlers given off by lightning from our own blue planet. Well…

Bill - The Voyagers also detected whistlers, and Juno is currently in its orbit detecting whistlers at Jupiter. The Voyager detections were part of a two-pronged assault back in 1979 on the question of whether there’s lightning on any other planet…

Another instrument on Voyager, the camera took pictures of the nightside of Jupiter and saw clouds that were lit from below by lightning flashes. So these two measurements, the whistlers and the images, prove beyond a shadow of a doubt that there’s lightning in the atmosphere at Jupiter. Back in 1979, this was the first planet other than Earth for which we knew lightning existed.

Izzie - This was a huge discovery, and across 40 years the team at the University of Iowa have provided radio and plasma wave receivers for more than 20 space missions. And whilst in space no-one can hear you scream, it appears there are signals which are shouting out.