On 29 April 2019, the Parkes “Maurriyang” Radio Telescope in Australia picked up an unusual signal while searching for signs of intelligent life elsewhere in the universe. The telescope was observing Proxima Centauri, the nearest star to the sun and host to a number of exoplanets that are potentially habitable.
The search was part of a project called Breakthrough Listen, which is hunting for technosignatures from other civilizations. These searches gather vast amounts of data. So the first task is to filter the interesting signals from the background.
In theory, a technosignature must have two important properties. The first is that it must be confined to a narrowband of frequencies with high information content, just like radio broadcasts on Earth. No known natural process can produce signals like this.
The second is that the frequency of the signal must drift in a way that is consistent with the motion of an exoplanet relative to the Earth. The drift is the result of the relative accelerations which causes a slight Doppler shift.
So Sofia Sheikh at the University of California, Berkeley and colleagues created a filter that automatically separates signals with these properties from all the others the telescope picks up. They found over 4 million of them.
