For more than 50 years, astronomers have pointed radio receivers to the sky and listened for signs of intelligent life — mostly, around stars like our own. Since that doesn't seem to be working out so well, a team of SETI researchers is now proposing something radically different: scanning the oldest and dimmest stars in the galaxy. Red dwarfs comprise roughly three quarters of all stars in the Milky Way. But despite their abundance, they have been given short shrift by researchers hunting for signs of extraterrestrial intelligence. Not any more. Over the next two years, the SETI Institute's Allen Telescope Array will scrutinise the vicinities of some 20,000 red dwarf stars, in one of the largest alien manhunts to date.
For decades, astronomers assumed that red dwarf stars — at best, only 10 per cent as luminous as the Sun — simply cannot harbour life as we know it. A planet would have to be closer than Mercury is to the Sun to potentially support liquid water. And in such a tight orbit, that planet would be tidally locked: one side constantly lit and roasting, the other frozen in eternal darkness.
But in the past few years, new exoplanet studies have suggested that the prospect of finding a habitable world around a red dwarf star may not be as bleak as we thought.
"Based on the Kepler data, researchers have extrapolated that between one in six and one in two red dwarf stars might have a planet in the habitable zone," Seth Shostack, a senior astronomer at the SETI Institute, told Gizmodo. What's more, new theoretical work indicates that even if such a planet was too hot on its day side and too cold on its night side, a twilight band in between could be downright balmy.
And from a SETI perspective, if life is able to gain a foothold on planets orbiting red dwarf stars, it could mean red dwarf systems are the best places to search for advanced life forms. That's because these stars are both extremely abundant (more chances for life to evolve), and on average, very old (more time for intelligence to emerge).
From a list of 70,000 candidate stars, astronomers will be scanning 20,000 over several of the so-called "magic frequencies". These are spots on the radio dial that are related to basic mathematical constants, which an intelligent civilisation might use to send out a deliberate signal.
A pessimist could argue that this survey, like the many before it, is extremely unlikely to turn up anything more than the background chatter of the cosmos itself. We have no way of knowing if intelligent life is out there, to say nothing of its interest in communicating with a bunch of barely space-capable mammals who seem to be teetering on the verge of a planetary apocalypse of their own making.
But we've only searched a tiny sliver of our cosmic backyard. "When you look at what's been done, the total number of stars that have been examined carefully is a few thousand," said Shostak. "This is a lot more."
And what if we hit the lottery and discover a much older, wiser civilisation that actually wants to chat? Maybe we can glean some knowledge about how to survive the next century. One can dream.
Artist's concept of two red dwarf stars in a binary pair. Image: NASA/Goddard