Saturn, Making Noise and Pleasing Researchers

The Cassini probe returns a wealth of sound from Saturn. Astrophysicist Donald Gurnett tells Christopher Joyce that it's especially helpful to hear Saturn, because the gas giant's cloudy atmosphere shields its surface from telescopes.

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SCOTT SIMON, host:

Turns out that outer space is not a quiet place, even when astronauts aren't out there clanking around. In fact, there's quite a racket going on, but you have to know where to go and how to listen. NPR's Christopher Joyce talked to an astrophysicist who has recorded sounds from a distant planet.

CHRISTOPHER JOYCE reporting:

Donald Gurnett would like to dispel an popular notion. Space is not exactly empty. The University of Iowa professor says that there's ionized gas out there; the technical term is a plasma. Waves travel through it and sometimes that creates radio signals, and for 44 years Gurnett has been listening. In 1997, he built an instrument to fly aboard the Cassini space probe, a joint European and US project to explore the ringed planet Saturn. Cassini got to Saturn last year, and Gurnett's instrument captured the audio moment.

(Soundbite of space sounds)

Professor DONALD GURNETT (University of Iowa): That was a recording made when we went across what's called the bow shock at Saturn.

JOYCE: Saturn's bow shock is a point in space where the solar wind, electrons and protons from the sun that wash through deep space, meets Saturn's magnetic field.

Prof. GURNETT: It creates a shock wave, kind of a bullet-shaped shock wave around the planet very similar to the shock wave that's formed around an airplane that's moving at a supersonic speed.

JOYCE: Now that Cassini is orbiting the planet, it's recording more sounds, some worthy of the best space opera.

(Soundbite of space sounds)

Prof. GURNETT: Now those are radio emissions produced by Saturn by the electrons that cause the aurora at Saturn just like you were on Earth. And these electrons come down a magnetic field at Saturn and they produce these really weird radio emissions.

(Soundbite of space sounds)

JOYCE: Even though Saturn is a giant ball of gas and the Earth's a pip-squeak speck of rock and water, their auroras work pretty much the same way. We call ours the Northern Lights. One of the mysteries of Saturn is how often it rotates. Because it's covered in gas and clouds, no one can see what's underneath or how fast it's spinning. But radio emissions give a clue.

(Soundbite of space sounds)

Prof. GURNETT: The radio emission from Saturn is controlled by its rotation. And so every time the planet rotates once, you get a burst of radio emission.

JOYCE: For the record, Gurnett points out that those sounds represent five days' worth of rotation. The frequency of all these sounds, in fact, has been adjusted so our ears can hear them.

Cassini's ride around Saturn has had its hazards. For example, there are those rings to deal with. Gurnett's instrument recorded the spacecraft crossing through part of those rings.

(Soundbite of space sounds)

Prof. GURNETT: The spacecraft's moving at very high velocity and when it runs into a dust particle, the dust particle just explodes. And we were detecting as many as a thousand impacts per second and that, you know, it sounds like hail hitting a roof.

(Soundbite of dust particles exploding)

JOYCE: Gurnett says the sounds from the radio part of the electromagnetic spectrum vary a lot depending on where you are in space. Most of the action is near planets with magnetic fields. When Gurnett's not flying World War II airplanes on Earth, he tries to imagine himself on the way to one of those planets.

Prof. GURNETT: Yeah, I really think of these spacecraft like I'm really there. I mean, you know, we can send commands to our instrument and change things and you listen to it, and it's like you're there.

JOYCE: Radio takes you there. Now there's an idea to end on. Christopher Joyce, NPR News.

(Soundbite of space sounds)

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