For the first time, scientists have recorded the eerie hum, which has baffled them for decades, in the ocean. The mysterious sound is inaudible to human ears but has been known for nearly half a century.
The planet is constantly expanding and contracting and that creates a steady sound, which is not audible to humans.
Scientists have been trying to record this mysterious low-frequency sound since 1959, but it was only in 1998, that a team of researchers found the sound was real. The mystery of the sound remained the same. However, scientists now believe that they would be able to solve the mystery with the latest recording.
Earlier, researchers believed that the interactions between the atmosphere and solid Earth caused the sound. "Later, different generation mechanisms proposed what they have in common is that the hum is generated by ocean infragravity waves," the study, published in the journal Geophysical Research Letters in November, read.
Geophysicists used ocean-bottom seismometers in the Indian Ocean to measure hum. The frequency of the hum is small and the sound of the ocean made it hard to hear the sound. Thus the team used "sophisticated mathematical technique" to remove the electronic glitches, ocean infragravity waves and seafloor currents.
"A low noise level is needed to observe the small signal amplitude of the hum," the researchers wrote in the study. "At the ocean bottom, the noise level at long periods is generally much higher than at land stations."
The team gathered the data from 57 seismometer stations placed in the Indian Ocean between 2012 and 2013. Researchers believe that the recording of the hum could be used to study the Earth's deep interior, which is widely unexplored.
"Station coverage in the oceans is much sparser than on land, leaving great parts of the Earth uncovered," the paper reads.
