The Sound of Music and Voices in Space Part 1: Theory

Abstract

While probes to other planets have carried an impressive array of sensors for imaging and chemical analysis, no probe has ever listened to the soundscape of an alien world. With a small number of exceptions, planetary science missions have been deaf. The most successful acoustic measurements were made by the European Space Agency's 2005 Huygens probe to Titan, but although this probe was spectacularly successful in measuring the atmospheric sound speed and estimating the range to the ground using an acoustic signal that the probe itself emitted, we still have no measurements of sounds generated by alien worlds. Although microphones have been built for Mars, the Mars Polar Lander was lost during descent on 3 December 1999, and the Phoenix probe microphone was not activated (because the Mars Descent Imager system to which it belonged was deactivated for fear of tripping a critical landing system). Instead of measuring acoustic signals that had propagated to the microphone from a distance, aerodynamic pressure fluctuations on the microphone (caused by wind on the surface of Venus in the case of the 1982 Russian Venera 13 and 14 probes, and turbulence during the parachute descent in the case of Huygens) masked the soundscape on these Venus and Titan missions. Given the lack of such data from these earlier missions, some early enthusiasts for acoustics in the space community are now skeptical as to whether it will ever have a useful role. However basing such an assessment on past performance presupposes that the sensor systems have been optimized for the environment in question.