Echo of life: Europa is Jupiter's third largest moon - and we may be able to listen for life below the surface.

Credit: NASA

Related articles

• Time ripe to search for life on Europa
• Coming soon: cloaked submarines
• Titan harbours hidden ocean
• Auroras brighten Ganymede's poles
• Enceladus has potential for life

NEW YORK: Beneath the icy crust of Jupiter's moon Europa could lie a vast ocean harboring alien life. Now experts suggest sending a giant stethoscope to listen out for it.

NASA is currently testing a submersible robot that could swim through Europa's waters, but Tim Leighton, an acoustic scientist at the University of Southampton in England, thinks there is an easier way.

Rather than drilling or melting through tens of kilometers of ice, a probe on Europa's surface could function like a sonogram – medical ultrasound – and use reflected sound waves to paint an acoustic picture of the moon's insides.

Let the sound do the work

"Why not let the sounds from the ocean travel to a probe sitting on the surface, letting the sound do the work for you?" Leighton said.

The idea was originally hatched by scientists from NASA, Stanford, MIT and the University of Colorado several years ago, but their acoustic models for Europa produced large errors when estimating the path soundwaves take through the interior of the moon. The errors arose because the earlier models were based on Earth's Arctic Ocean, where the ice crust is only about 3 km thick and the water is only about 1 km deep, Leighton said.

In contrast, recent studies suggest Europa has a diameter only a quarter that of Earth, an ice crust that is more than 20 km thick, and an ocean that is probably 100 times deeper than the Arctic Ocean.

In a new study, detailed in the Februrary issue of the journal Icarus, Leighton and his team corrected for these errors and found that the idea of using a a surface probe to explore Europa's interior using sound is indeed feasible.

Unravelling the signals

The probe could send and receive sound waves or listen for acoustic signals generated by seismic events or meteor showers. As the sound waves travel through Europa's oceans and ice layer, they would change in a way that reflected moon's interior environments.

Michael Buckingham, an oceanographer at the Scripps Institution of Oceanography in San Diego, U.S., thinks Leighton's new model more accurately reflects the current knowledge about Europa.

"By unravelling the received [sound] signals, it may be possible to extract the information they carry about the inner structure of Europa," Buckingham said.