Aliens could be talking to us right now. This scientist is listening.

Sofia Sheikh is a PhD candidate in Astronomy and Astrobiology at Pennsylvania State University. This is her story from the field as told to Charlie Wood.

The search for extraterrestrial intelligence has progressed rapidly in the past few decades. Back in the 1960s, researchers would literally tune the radio dial, hoping to hear artificial patterns in the static that would prove we’re not alone. But they could only listen to one slice of the spectrum at a time. Now, thanks to massive radio telescopes, astronomers can pick up wide swaths of it at once. Breakthrough Listen, a global research group I am part of, is investigating more than a million stars for single-tone signals akin to our AM/FM stations.

In 2017, I led a study of 20 intriguing stars—ones from which Earth’s transit in front of our sun is visible. If a civilization in this zone can see us, perhaps they’re reaching out. It took almost five months for every star to rotate into view and another two years to sort through the hundreds of gigabytes of radio crackling we gathered.

During my analysis, one tone seemed powerful and clear, as you would expect an artificial transmission to be. But when I looked more closely, I noticed that the signal’s frequency barely shifted. This implies its source is stationary relative to the telescope rather than zooming around as a planet, moon, or spacecraft would. My money’s on something like a cell tower. That’s 20 stars down, millions to go.

This story appears in the Fall 2020, Mysteries issue of Popular Science.