The team found that at its fastest, sound can travel at 36 km (22.4 mi) per second. That's more than 100 times faster than its average speed through air, which is 343 m (1,125 ft) per second, and three times faster than its previously-measured top speed of 12 km (7.5 mi) per second, through diamond.
So what medium lets sound travel at such a high speed? According to the new study, it's solid atomic hydrogen. This form of the element only occurs under immense pressure, such as that found at the core of gas giant planets like Jupiter. Under those conditions, hydrogen is compressed into a metallic solid that can easily conduct electricity – and, it turns out, sound.
The researchers came to this conclusion by studying two fundamental constants – the fine structure constant and the proton-to-electron mass ratio. These numbers play huge roles in a variety of scientific fields, including in this case, material properties.