Astronomers searching for signs of extraterrestrial intelligence may have been missing alien signals in part of the radio spectrum that has not recently been explored.

Most radio SETI (Search for Extraterrestrial Intelligence) surveys have focused on frequencies between 1.42 and 1.66 GHz. This range is known as the “water hole” because it lies between the natural radio frequencies emitted by hydrogen and hydroxyl, two molecules whose combination forms water.

Scientists have long thought that this relatively quiet part of the radio spectrum would be a logical place to communicate, as a technologically advanced civilization might recognize the significance of hydrogen and hydroxyl and be likely to transmit and listen there.