Where are the aliens hiding? Maybe talking to each other on the wrong frequency, one we have not yet looked at. Imagine if the solution to the Fermi Paradox, the famous quip about not being able to find these beings, came down to a simple change in where we're looking. New research investigates.

Most of the Search for Extraterrestrial Intelligence (SETI) in radio waves specifically focuses on the frequencies between 1.42 and 1.66 GHz, with plenty of reasons why. To begin with, this range is among the parts where the Earth’s atmosphere is transparent to radio waves, so we can use observatories on the ground.

The two frequencies also sit between two famous lines: on one hand is the emission from hydrogen (the notorious 21-centimeter line), and on the other is the hydroxyl molecule, or more simply, OH. Combined together, hydrogen and hydroxyl make water.

Both hydrogen and hydroxyl are common and bright in the universe, but the frequencies in between are wonderfully quiet. The water connection has led researchers to call this the "water hole." If you were trying to send signals across the stars, picking a frequency between these two would be a smart choice.

Lots of signals we use on Earth, from TV to radar, can fall into this particular water hole. Earth could already be discoverable by nearby star systems due to telephone communication signals and even airport radars.

It's just really about understanding whether we're alone or not; that's the biggest question. I hope not!

Still, there is no reason why aliens might not be communicating or accidentally emitting signals in other wavelengths.

For this reason, Louisa Mason, a PhD researcher at the University of Manchester, used archival data from the Atacama Large Millimeter/submillimeter Array (ALMA) to expand this search.

“In SETI, the first best guess was looking at a specific wavelength about 1.4 to 1.6 gigahertz, partly because the galaxy goes quiet,” Mason told IFLScience.

“So, we thought that maybe if intelligent life wanted to send a signal, they've got a better chance of getting over the noise from the galaxy, from the universe.”

The logic of that choice is undeniably solid. It’s a great range of frequencies, and any species that is water-based would be familiar with that signature. There’s one snag though… which is the usual snag.

Continue reading: iflscience.com/first-seti-surv…