Studying the ice sounds would allow researchers to see if there was a connection between the moon's orbital period and the ice fractures, which occur on Europa once every 30 seconds. Meteors impact Europa about once a month and these also could be used as sound sources. By inserting vibration-sensitive hydrophones in the water, researchers used ambient sound to listen for changes in noise levels. They found that noise levels increased when winds and currents put stresses on the ice. The ice is very sensitive and conducive to sound.
Sound waves made by large fractures go through the ice and penetrate into the ocean.
These low-frequency sound waves, akin to those created by whales, get trapped and can propagate hundreds of kilometers through the water. Even if they can't be heard, instruments can pick up their vibrations from a distance. In addition to Makris, the research team includes ocean engineering postdoctorate associates Aaron M. Thode and Michele Zanolin and graduate students Sunwoong Lee, Purnima Ratilal and Joshua Wilson. This work is funded by the Office of Naval Research.