The Sounds of Titan

In 2005, the European Space Agency's Huygens probe descended to the surface of Saturn's moon Titan. Microphones aboard Huygens recorded the sounds of descent and landing.

The Planetary Society supported University of California Berkeley scientist Greg Delory—who also worked with us on the Mars microphone project—to help ESA quickly process the audio data after Hugyens’ landing so members of the public could hear what it would sound like to plunge through Titan’s haze.

The landing (ver. 3)
.mp3 format (82k)

This version of the landing sound attempts to correct for the fact that the "bump" of Huygens' landing actually occurred over a much shorter time period than the HASI acoustic sensor was able to detect. In the previous version (see below), the landing occurs as a slow fade of sound. Delory assumes that the landing occurs over a much shorter time, instructing his software to sense a very sudden drop-off in amplitude and plot it as a stepwise (rather than smooth) transition in the output sound. In addition, he amplified the highest frequency (highest pitch) component of the sound right at the landing to bring out more detail from the landing sound.
HASI-PWA Team (instrument and data) / The Planetary Society (processing)

The landing (ver. 2)
.mp3 format (728k)
This sound sample overlaps the landing, at which point all becomes much more quiet. The landing occurs as a slow fade of sound rather than a sharp "thud" because of the 2-second, or lower, resolution of the sound data, and because Delory's sound processing algorithm is designed to smooth amplitude jumps in the acoustic sensor data.
HASI-PWA Team (instrument and data) / The Planetary Society (processing)

The entire 2.5 hour descent in 10 seconds (ver. 2)
.mp3 format (69k)
This is the entire set of data compressed into 10 seconds of listening time. There is a marked change near the end of the clip, representing sound recorded after the landing.
HASI-PWA Team (instrument and data) / The Planetary Society (processing)

Early in the descent (ver. 2)
.mp3 format (378k)
Data from early in the descent through the Titan atmosphere, played back at the actual rate at which the data were recorded. Some event during the descent causes an amplitude (loudness) increase in the recorded sound.
HASI-PWA Team (instrument and data) / The Planetary Society (processing)

After landing (ver. 2)
.mp3 format (253k)
These data were taken after landing on Titan; its amplitude (loudness) is much lower than the "descent" clip.
HASI-PWA Team (instrument and data) / The Planetary Society (processing)

The following sound files were produced by Peter Falkner and Roland Trautner, members of the HASI team.

During the descent
.wav format (356k)
"Lots of acoustic noise" is present in this data, according to Peter Falkner.
Credit: HASI-PWA Team

After the impact
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This one comes from after impact, when the sound was damped by Huygens sitting on the surface; all the sound we can hear is likely internal to the microphone, according to Peter Falkner, a member of the HASI-PWA team.
Credit: HASI-PWA Team

Sounds from Huygens' Radar Altimeter

Huygens approaches the surface
.mp3 format (996k)
This is a reconstruction of a signal generated by the Huygens radar altimeter. While descending toward Titan, the frequency of the instrument's "blanking signal" was varied until the radar achieved "lock," which means that the radar signal returned from the surface was detected and exceeded a pre-defined signal-to-noise level. At the beginning of the descent the radar was not locked, then it went through some intermediate short spurious locks (the 'Techno' sound), until the probe was close enough to the surface (between 35 and 40 km) to receive a constant strong return signal.

Once the radar locked, the radar altimeter's blanking signal frequency was indirectly proportional to the altitude, meaning that high altitude corresponds to low frequency (low pitch), and an approach towards the surface corresponds to rising audible frequency (high pitch). Throughout the rest of the Huygens descent the radar stayed locked, returning accurate altitude data and beautiful spectra of the return signal, which contain information on Titan's surface topography.

In order to reflect the properties of the surface sensed by the radar, the reconstructed blanking signal is modulated by the strength of the reflected signal, which means that loud sound corresponds to high surface reflectivity, while low loudness corresponds to high absorption. Roland Trautner, a member of the HASI team, says "I reconstructed the signal from PWA altitude and spectral data in order to allow everyone to get a feeling for the radar signals in an intuitive way."

Sounds Manufactured from Radio Signals Between Huygens, Cassini, and Earth

Cassini's Radio Ear on Huygens
.mp3 format (956 k)

The 1-minute-long file covers 4 hours of Huygens' lifetime, from the moment the parachute opened to a little over an hour after the unexpectedly soft landing. The frequency (pitch) of the sound file is related to the strength of the signal as detected by Cassini -- when the sound is low-pitched in the first part of the file, Cassini detected a strong signal from Huygens, and when the sound is high-pitched at the end, the signal seemed relatively weak. The marked change in the pitch at about 43 seconds into the sound file represents the moment that Huygens landed, after which it was no longer moving (although Cassini was). On top of the general decrease in signal strength over the course of the descent, there is a fast, repeating "chirping" sound, which is irregular at first, then gets more regular and slower over the course of the descent, and finally disappears after the landing. These shorter-period variations in the strength of Huygens' signal to Cassini result from Huygens' spinning and swaying under the parachute. The spin rate was fastest at the beginning of the descent (up to around 12 revolutions per minute), and slowest near the end (perhaps around 1 revolution per minute); of course the probe was no longer spinning at all after it landed. Also, Huygens swayed more at the beginning of the descent, which was unexpectedly bumpy. The spinning and swaying changed the orientation of Huygens' antenna with respect to Cassini, which in turn affected the strength of the signal that Cassini detected. The sounds were produced by Ralph Lorenz, a planetary scientist at the University of Arizona, from data formatted by Miguel Perez of the European Space Technology Centre (ESTEC).

Huygens' Carrier Signal at Green Bank
.wav format (411 k)

Little information was published with this sound, which was posted on the website of the Joint Institute for Very Long Baseline Interferometry in Europe (JIVE), except that it represents "Huygens as detected by the Green Bank Telescope during the descent."