What does a waterfall sound like in space?

The answer to this fascinating question may be found on Titan, Saturn's largest moon.  University of Southampton scientist Professor Tim Leighton has speculated how the sound of splashing liquid in deep space might differ to that heard on Earth - and it's possible that his theory could be proved later this year by NASA's Cassini mission to Saturn.  In the meantime, he has recreated the sound he believes it makes and put it on the Internet.

On Thursday 1 July 2004, NASA's Cassini space craft will go into orbit around Saturn where it will study the planet, its moons and rings for four years.  However, in Professor Leighton's view, possibly the most interesting aspect of the Cassini mission, is the European Space Agency's probe Huygens, which will study Titan.  After a seven-year journey strapped to the side of Cassini, the probe will separate from it on Christmas Day 2004 and coast for 20 days before parachuting through the thick atmosphere to become the first man-made object to land on the moon of another planet on 14 January 2005.

Titan's thick smog has prevented earlier spacecraft photographing its surface, but there are suggestions that the moon may be home to seas and streams made, not of water, but of liquid ethane.  The main focus of Huygens' mission is sampling the smog-laden atmosphere, but three minutes of battery time will be used for investigations immediately after landing.  Although the probe's microphone is on board primarily to monitor atmospheric buffering, Professor Leighton of the University's Institute for Sound and Vibration Research, has suggested that, were the microphone to detect a splash-down as opposed to a crunch on landing, the question of what a splash in space might sound like would be answered.

Professor Leighton, who has speculated for several years on sounds in space, explains: 'I began asking whether the noise of splashes which is so familiar to us on Earth would be recognisable in a sea of liquid ethane at a temperature of 180 degrees below zero.  NASA's specially-commissioned painting of a waterfall - actually a methane fall - on Titan inspired me to attempt to predict how it would sound.  I set up the equations and measured the sound of a small waterfall in nearby Romsey.  My colleague Dr Paul White then processed the signal to obtain what we believe would be the sound of a methane fall on Titan.

'Given that the last decade has seen an explosion in the amount we can learn about the oceans simply by listening to them, from storms to seabed properties to coastal erosion, acoustics represent a potentially exciting and comparatively low-cost method of space exploration.'

Professor Leighton outlines his ideas for the role of acoustics in space exploration in an article entitled 'The Sound of Titan' to be published in the July/August edition of Acoustics Bulletin.  The sound of the methane fall as calculated by Professor Leighton and Dr Paul White can be heard at www.isvr.soton.ac.uk/fdag/uaua.htm