A role for acoustics in space exploration?

Over the last 10 years the field of 'acoustical oceanography' has blossomed, whereby we obtain extraordinary amounts of information about the ocean by examining the propagation of sound within it. A sound pulse, traveling at 1.5 km per second,  can be used to monitor ocean temperature, plankton, undersea 'weather systems', the nature of the seabed and its contents, the million-tonne sediment loads carried down estuaries, and the billions of tonnes per year of atmospheric gas which dissolves into the oceans and exsolves out of it, and many more environmental parameters. Acoustics offers techniques which are far cheaper and closer to 'real-time' than sending out ships which trawl instrument packages for months through the oceans. 

Many of these techniques involve the experimenter sending a pulse through the water, and seeing how it reflects, attenuates, etc. However the generation of such pulses takes energy, and whilst this is often not a problem on Earth, low-energy systems are particularly valuable in space exploration. The most energy efficient form of Acoustical Oceanography, and the most rugged, comes from passive acoustics, where instead of sending out a pulse of sound, the experimenter simply listens to the sounds in the environment. A further advantage for space exploration of such acoustic information is the ease and efficiency with which it could be coded and transmitted back to Earth: note by how much wireless transmission pre-dated televisions, and how voices on mobile phones pre-date picture technology - or note the difference in downloading time of music from the internet as opposed to video. Space exploration has placed a higher premium on images that on sound, but the above advantages are considerable.

But even given these advantages, and the fact that probe lifetimes might be extended by using passive acoustics in place of some other sensors, is the acoustic information valuable? In some circumstances, the answer would be no. But for a probe landing on another world, especially one like Titan with a thick atmosphere and possibly seas, acoustic information may not only be cheap to power and cheap to transmit back to Earth, but it may provide new and exciting information. Look around your room. The images you see tell you a great deal about it. But they don't tell you what is happening behind you, or on the other side of the wall, or in the street beyond your line of vision. Now close your eyes and ask yourself what is happening in those places. Even if you find, as I do now, that no-one is speaking in the room next to you, that is new information! If they are speaking, you know even can tell their mood, and what they are thinking about. How many times have you diagnosed trouble in a car or washing machine from its sound? Given how much we have learned about interpreting our environment using the sounds within it, particularly in the oceans, perhaps the role of acoustics in space exploration should be re-evaluated. For an overview of out space acoustics works, click here. This project discusses how Titan might sound. Follow the links to hear the estimated sound of a 'waterfall' on Titan, of a splashdown on Titan, and to find out how it was done.

 This page was last updated by TG Leighton, 6 August 2004