ET search finds nothing

The hunt for alien microwaves finds only silence.

As far as signs of intelligent life go, it’s as quiet as the grave from here to 50 parsecs – 1.55 million billion km – in every direction.

That’s the preliminary finding from the first year of the Breakthrough Listen Initiative (BLI), the program on a 10year mission to seek out signals from extraterrestrials.

The BLI project ultimately aims to monitor microwaves emitted near one million stars; the first-year results cover data on just 692, collected by the Green Bank Telescope (GBT) in West Virginia. So they are hardly conclusive. Neither, however, are they encouraging.

With significant private support including $US100 million from Russian oligarch Yuri Milner and his wife, BLI has paid to use two large radio telescopes – the GBT and the Parkes Radio Telescope in Australia – and the Automated Planet Finder optical telescope at Lick Observatory in California, to cover vastly more of the sky than previous searches for extraterrestrial intelligence.

Researchers led by astronomer Emilio Enriquez from the University of California, Berkeley – the home of the Breakthrough Listen Science program – analysed data from the GBT looking specifically for transmissions within the ‘microwave window’ – frequencies between 1 and 10 gigahertz (GHZ).

It is a search strategy suggested in 1959 by astronomers Philip Morrison and Guiseppe Cocconi. They recognised the microwave window as a goldilocks zone for interstellar transmissions: lower frequencies would experience interference when passing through galaxies emitting low-frequency radio waves; higher frequencies would tend to get absorbed by Earth-like planetary atmospheres.

Signals from space within the microwave window are thus automatically of interest to ET hunters – even more so if they display significant variation, an indication of possibly encoded data.

The search has focused on the lower end of the microwave window, looking for signals between 1.1 and 1.9 GHZ. The rest of the range will be covered over the next few years.

Early results had been promising, with 11 signals deemed interesting enough for further analysis; but all of them turned out to have originated on Earth. In effect, the telescopes were picking up our own background babble.

In their paper, published on the preprint server arxiv hosted by Cornell University Library, the researchers report that “none of the observed systems host high-duty-cycle radio transmitters emitting between 1.1 to 1.9 GHZ”.

But a modicum of hope is left. There is still a chance of transmitters within 50 parsecs of Earth – though the estimated probability is less than 0.1%.