The false alarms picked up by the Australian Long Baseline Array probably came form Earth orbiting satellites, say the team.
Of course, this doesn't exclude the possibility of intelligent life in the Giese 581 system or even exclude the possibility that these ETs might use radio signals to communicate.
Instead, it places limits on the strength of these signals and not particularly onerous ones at that. Rampadarath and pals say their instrument would have picked up a broadcast with a power output of at least 7 megaWatts per hertz.
To put that in context, on the slim chance that Gliese inhabitants had been broadcasting directly to Earth using an Arecibo-style dish, Rampadarath and co would have easily picked up the signal. (Arecibo is a 300 metre radio telescope in Puerto Rico).
On the other hand, the ordinary radio transmissions like those we continually broadcast into space, would have been far too weak to be picked up by the Australian team.
That's not to say that this kind of observation won't be possible in future. The Australian array is by no means the biggest of most sensitive instrument available today.
What's more, astronomers are planning a new VLBI telescope called the Square Kilometre Array which will have the sensitivity to pick up broadcasts of a few kiloWatts per Hertz from 20 light years away.
There are no shortage of targets. At the last count, astronomers had found around exoplanets that sit in their habitable zones (meaning they're warm enough for liquid water). These places are of intense interest.
Time on VLBI telescopes is precious and difficult to come by. But the prize here is of almost incalculable value--the discovery of intelligent life beyond the Solar System.
So it wouldn't be a complete surprise if radio astronomers found ways to hunt more often for radio broadcasts from new and exciting exoplanets.
Ref: arxiv.org/abs/1205.6466 :The First Very Long Baseline Interferometric SETI Experiment
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