space
Could the strange noises picked up by a U.S. graduate student’s balloon experiment really have come from outer space? Creative Commons

Crop circles and UFO sightings weren’t getting their message across, so aliens have apparently started dropping breadcrumbs beyond Earth. A recent NASA experiment involving a balloon and infrasound microphones picked up some mysterious noises from the edge of space. Scientists have their theories about what the recordings could be, but at this point, the true origin of the sound remains a mystery, according to Live Science.

The research, the first of its kind in 50 years, involved sending a helium balloon to 22 miles above Earth’s surface, or about three times higher than the altitude planes fly at. Attached to the balloon were infrasound microphones, recording devices that can pick up sound at frequencies below 20 hertz per second – the lowest threshold of the human hearing range.

It was the highest point from which an infrasound recording had ever been taken. The experiment, conducted in August 2014, was designed by University of North Carolina at Chapel Hill graduate student Daniel Bowman as part of NASA’s High Altitude Student Platform project, which was launched in 2006. “I was surprised by the sheer complexity of the signal,” Bowman told Live Science. "It sounds kind of like 'The X-Files.’" The balloon floated over New Mexico and Arizona for 450 miles, according to scientists.

While the origin of the bizarre space noises hasn’t yet been determined, scientists say the explanation might disappoint alien enthusiasts. The sounds could have come from something as non-extraterrestrial as crashing ocean waves, the vibration of the balloon’s cable, or air turbulence. The environment is full of infrasound from both natural and manmade sources. Most of them don’t travel from a galaxy far, far away.

This isn’t the first NASA-funded balloon experiment to take flight in recent years. In March, World View, a private space exploration company based in Arizona that wants to one day send tourists in to the near-space frontier, released a 331,000-cubic-foot helium balloon into the sky carrying two student experiments – one to monitor cosmic rays, and the other to measure the distribution of gases in Earth’s atmosphere.

Listen to the alien sounds here: