Acoustic Instruments in Planetary Exploration:
The Past, Present, and Future

Martin C. Towner - martintowner@googlemail.com
CEPSAR, The Open University
Milton Keynes, UK

Popular version of paper 3aPAb1
Presented Wednesday morning, June 6, 2007
153rd ASA Meeting, Salt Lake City, UT

Only a few planetary missions to date have deployed acoustic instruments, and most of them have been used to study the environment, such as listening for thunder. No acoustic instrument has been used to investigate physical properties in detail. The Mars Microphone was slated to make extensive recordings on the planet surface, but it was deployed on the Mars Polar Lander, which sadly, lost radio contact with Earth before it reached the surface. The three successful missions are Venus landers from the Soviet Union in 1981, Venera 13 and 14, and the recent Huygens probe to Saturn’s moon Titan. Venera 13 and 14 recorded the sounds on the surface of Venus, hearing the noise of the on-board instruments and the whistle of the Venusian wind. Huygens listened for thunder during its two-and-a-half hour descent through Titan’s atmosphere, used an acoustic altimeter to detect the approaching ground and measured the speed of sound in the gas during descent. The environments of Venus and Titan are very different from that of the Earth in both temperature and pressure, and specialized instruments were designed in both cases. The following talks in this session will describe some of these results in more detail, in particular the acoustic results from the recent Huygens mission.

Acoustic sensors to date have tended to be a minor part of a probe’s payload, but small and simple sensors can still make a valuable scientific contribution. They also have a strong potential for public engagement, by helping to “bring to life” the environment on other planets, as was the intent of the Mars Microphone project, also described in a separate talk at this meeting (Delory, 3aPAb2). However, the prospects are good for acoustic instruments to play a more direct role in future scientific exploration, moving from just passively recording the environment to being sensing tools in their own right. This arises for proposed future missions focusing on Mars, Venus and Titan, which tend to have atmospheres significant enough for studying their acoustical effects. These missions will benefit from more capable spacecraft flight and mobility, which require more remote sensing than would be needed on a stationary lander. More long-term plans for the exploration of possible under-ice oceans on places like Jupiter’s moon, Europa, will require advanced acoustic instrumentation to navigate and sense local conditions in the search for possible life.