A team of astronomers is proposing a new way to hunt for intelligent life that sounds rather obvious when you think about it: We need to be the aliens. Or at least, we need to put ourselves in their shoes and think about where in the sky they can see us. Finding other beings like ourselves would change the world, but it ain't going to be easy. The Search for Extraterrestrial Intelligence (SETI) has been hunting since the 1960s, and it's only managed to scan a small drop of the sky for radio signals. Astrobiologists have proposed many ways that we could narrow the search, from focusing on star-rich globular clusters to directing our instruments toward the Galactic centre, where higher rates of star formation imply more possibilities of finding habitable worlds -- or perhaps more importantly, where a really clever intelligent species might plant a beacon.
Another way to think about the problem is to ask where in the cosmos alien life can see us. If there are people out there searching for habitable worlds in the same way we are, where would they have to be to spy a world that's 70 per cent ocean-covered, with a nitrogen-rich atmosphere, orbiting 149.6 million kilometres from a G-type star, about halfway between the galactic centre and the Milky Way's rim?
If our cosmic neighbours can see Earth as it transits the Sun, then, René Heller and Ralph Pudritz argue in the journal Astrobiology, it's possible they have already found us. And if that's the case, they might be sending out a signal. That's why Heller and Pudritz argue we should turn our ears to Earth's "transit zone", a thin slice of space containing approximately 100,000 potential stars.
100,000 still sounds like a lot of targets, but it's way less daunting when you consider the 100 billion stars in the Milky Way galaxy -- and it happens to be about the volume of space we can see with today's radio telescopes. Last year, Russian billionaire Yuri Milner kicked off Breakthrough Listen, a $US100 million effort to discover alien intelligence. That means that SETI now has both a solid funding source and a potential roadmap.
As with any "we should be looking here for aliens!" argument, there are a thousand caveats and unknowns. We don't know that aliens are out there at all. If intelligent beings do exist, there's no reason to think they're using telescopes and radio waves to study the stars. In fact, many philosophers and SETI researchers will argue that any alien civilisations we can detect are likely to be very old -- and thus, they might vastly exceed our technological capacity in every conceivable way. Perhaps, then, it really isn't so wise to be looking for them. Perhaps they don't want to be seen. And so forth.
But it's in our nature to explore and to ask these questions. And if scouring Earth's transit zone slightly increases the odds of us ending our cosmic loneliness -- and even better, finding intelligent life that's roughly comparable to us in technology -- I say it's a project well worth our effort.
Top image: Abel 1689 Galaxy Cluster, via Wikimedia