Twin spacecraft have captured the clearest sounds yet from Earth’s radiation belts — and they mimic the chirping of birds.

NASA’s Van Allen Probes have been exploring the hostile radiation belts surrounding Earth for just three months. But already, they’ve collected detailed measurements of high-energy particles and radio waves.

Scientists say these waves can provide an energy boost to radiation belt particles, somewhat like ocean waves can propel a surfer on Earth. What’s more, these so-called chorus waves operate in the same frequency as human hearing so they can be heard.

A University of Iowa physicist played a recording of these high-pitched radio waves at a conference Tuesday in San Francisco. Craig Kletzing says it sounds like the chirping of “alien birds” and crickets.