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Sounds of Titan


The Huygens probe transmitted sound to Earth from farther away in the solar system than any spacecraft ever had before. Below, explore a collection of intriguing noises from the Cassini-Huygens mission, and hear explanations of each sound from research scientist and Planetary Society education director Bruce Betts.


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Sound in Space

Sound in Space
What is sound and how does space affect it?

Huygens' Descent

Huygens' Descent
Ride along on the outside of Huygens as it parachutes through Titan's atmosphere at nearly 200 miles per hour.

Carrier Signal

Carrier Signal
Hear Huygens' "voice," the tone it emitted so Cassini and engineers on Earth could locate the probe.

Listen Listen Listen


Radar Altimeter

Radar Altimeter
Experts converted radar echoes that Huygens received during its descent into these audible sounds.

Radio Ear

Radio Ear
Huygens talked to Cassini using this alien-sounding signal.

Titanized Sound

"Titanized" Sound
Bruce Betts's voice would sound dramatically different if he were standing on Titan.

Listen Listen Listen


Transcript of Bruce Betts's Audio Explanations

Sound in Space
Sound is basically pressure waves that are moving through some medium. So the sound that we usually hear is going through the air. And it's transmitted as what are called "longitudinal waves." So they push back and forth kind of like a slinky if you push it back and forth. And what that does is in our ears it vibrates the eardrum. So you get no sound if you're in the vacuum of space, but you get sound if you're either in air or in a solid or liquid. How loud something is at a given distance, or what frequencies of the sound—whether high frequencies or low frequencies—get damped out or go away faster will depend on the medium you're in.


Huygens' Descent
So basically what you are hearing is the sound of wind noise transitioning to a lack of wind noise. The Huygens probe had an acoustic sensor, basically a microphone, to try to detect thunder if you actually had lightning. The acoustic sensor would sample two-second intervals in certain frequencies and create this kind of average sound that changed as you descended through the atmosphere. And so this is a transition where you hear something real in this data, despite the fact that it's sounding like Crrrrrrrrrrrrr. It actually goes from that to something very silent, which does represent when the lander landed a billion miles away, by far the farthest we've ever transmitted something resembling sound in our solar system.


Carrier Signal
When you're sending data from a spacecraft you will have a so-called carrier signal. It's basically broadcasting a tone—if you think of it in audio terms— broadcasting as strong as it can get signal at one particular frequency. And that they were able to pick up from Earth, it turns out. And then Cassini used it to lock onto Huygens.

You can do one critical piece of science with the carrier signal alone and that is measure the Doppler shift of that signal—the old oncoming train concept, where you hear Eeeeeeeeeeoooooooow. So the frequencies change if something's going away from you or coming towards you, and it depends on velocity. So they were able—even from Earth—this just amazed me, using large antennas on Earth, to analyze the carrier signal and how the frequency shifted, and from that get an idea of the velocity of the Huygens probe as it went through the Titan atmosphere and how it changed with altitude, for example, and with shifting winds. It's just amazing at those distances.


Radar Altimeter
What you're hearing is the Huygens' radar altimeter data that has been converted to sound. Basically, as the spacecraft came down, they bounced radar off the surface to figure out how far down it was before they were going to touch down. And so what you're hearing is, they've coded this as related to altitude, and you're hearing it as it approaches the surface.


Radio Ear
Huygens did not have the capability to transmit data back to Earth. And it relied on the Cassini spacecraft flying overhead. Instead of having to carry something big enough to transmit the billion miles, it sent things to Cassini to send things back the billion miles. So this is some very creative interpretation of how strong the signal was coming from the Huygens lander to the Cassini spacecraft.

And so it's combining the different factors of signal strength and frequency into sound to give some idea of the probe going through the atmosphere. But it's something really, really unrelated to sound in its initial physics.


"Titanized" Sound
Titan is the only moon in the solar system that has a big, thick atmosphere. And it actually has a pressure on the surface that's comparable to Earth. It's about one and a half times the surface pressure on Earth. But it is also mostly nitrogen, just like the Earth's atmosphere is mostly nitrogen. But it is down at temperatures that are something like 100 Kelvin, so, like -300°F—so extremely cold. Having that cold temperature actually ends up leaving you with sound traveling sounding very similar to what the surface of Mars sounds like.



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