Have we discovered alien intelligence? It’s the kind of story to make you giddy – like a kid who hears Santa Claus scrabbling on the roof.
Two stories have recently toed the line between science and science fiction – but should we take them seriously?
Here’s what you need to know.
Have we detected an alien radio signal from a star 94 light-years away?
Almost certainly not.
In May 2015 astronomers detected a strong, high-frequency radio signal from HD 164595 (a sun-like star in the constellation Hercules, about 94 light years away), according to a presentation by the Italian astronomer Claudio Maccone due to be given at the International Astronomical Meeting in Mexico next month.
At first glance, the signal seems just what the Search for Extra-Terrestrial Intelligence (SETI) Institute has been searching for.
But alas, the signal is almost certainly not of alien origin.
The signal has not been detected since. And when SETI pointed the Allen Telescope Array at the star over the weekend, it detected nothing.
Second, the signal is almost unbelievably strong. To reach us at this strength, an alien civilisation would have had to blast it directly at us with a power of 50 trillion watts (equivalent to humanity’s entire energy usage at any moment).
Meanwhile, if it was a general broadcast in all directions, it would need about 100 million times more energy than even that. That sort of wanton energy use seems unlikely, even for an advanced civilisation.
So what was it?
Perhaps a mundane signal was magnified to huge proportions by gravity, just like a magnifying glass can focus sunlight to melt tar. Or perhaps the signal arose with something manmade, picked up mistakenly by the Russian detector. Until the signal reappears, we may never know (and until it reappears, it’s probably not worth worrying about).
Have we discovered an alien megastructure?
Probably not.
In October last year, astronomers at Yale University led by Tabetha Boyajian described a star so weird they began to call it the “most mysterious star in the galaxy.”
The star KIC 8462852 (also known as Tabby’s star, or the WTF star) is a bigger and hotter version of our sun, though at 1,480 light-years away is too dim to see with the naked eye.
KIC 8462852 was one of 150,000 stars monitored by the Kepler space telescope between 2009 and 2013. Kepler is a planet-hunting telescope designed to look for periodic dips in brightness as a planet passes in front of its host star, blocking some of its light.
In 2011 and again in 2013, KIC 8462852 dimmed by as much as 20%, suggesting something huge might be in passing across the star. (Even a planet as large as Jupiter would only block about 1% of the light.)
Whatever was blocking the light was huge – possibly half the width of the star itself.
But more evidence from Kepler suggests the shadows are cast by many irregularly shaped objects passing across the face of the star, rather than one large one.
Natural explanations
Boyajian’s team and other astronomers have proposed many different possible explanations for this behaviour.
They’ve concluded, for example, that KIC 8462852 is not the kind of star that naturally varies in brightness.
Another explanation might be that the star has a very busy solar system, with dust, disks or protoplanets ganging around. But such solar systems typically envelop very young stars. KIC 8462852 has the appearance of a mature star and is not in a star-forming region.
The most favoured natural explanation, as proposed by Boyajian and developed by others, is probably that the dimmings are caused by a family of comets passing in front of the star. This family would have originated as a single comet, which was ripped apart after a close encounter with a large planet, or the star itself.
Unnatural speculation
But another explanation, which has still not been ruled out, is that the star is enveloped by an alien construction project of extraordinary proportions.
The idea was proposed by Jason Wright, an astronomer at Pennsylvania State University. “Aliens should always be the very last hypothesis you consider,” he told The Atlantic, “but this looked like something you would expect an alien civilisation to build.”
The structure we’re talking about here would be something like a Dyson sphere – built from millions of solar panels in orbit around a star and making use of almost all of a star’s energy output.
The idea was first described in the 1930s sci-fi epic Star Maker, and popularised in 1960 when the English-born American physicist Freeman Dyson explored the idea in more detail.
A study led by Wright concluded that the KIC 8462852 signal has “all of the hallmarks” of a Dyson sphere.
Attributing the signal to a giant alien construction project is certainly tempting. After all, with astronomers estimating there are about 40 billion potentially habitable planets in our galaxy, it’s something of a mystery why decades of SETI searches have so far proved fruitless.
But on the other hand, the data doesn’t fit the Dyson sphere idea too well either.
The problem boils down to thermodynamics. Inevitably, some of the energy harnessed by a Dyson sphere would be emitted as waste heat.
In Dyson’s original 1960 paper, he suggested looking for sources of this waste heat as part of a search for extraterrestrial intelligence.
But Tabby’s star doesn’t seem to emit this radiation. And SETI scientists searching for radio signals from the star have also come up with nothing.
From the “canals” on Mars in the late 19th to the periodic LGM-1 (“Little Green Men”) signal of the 1960s, astronomers have often attributed mysterious phenomena to intelligent beings. Yet these explanations have been replaced by something altogether more mundane.
The supposed canals turned out to be optical illusions, while the LGM signal is now recognised as a pulsar (a kind of star that rapidly spins emitted light like a lighthouse).
Perhaps these explanations come about from our tendency to credit structure to a creator. Perhaps they come from wishful thinking – after all, who hasn’t stared at the stars and wondered?
Or perhaps they simply come from a failure of our imagination. As Boyajian says: “One thing for sure is that nature has a much better imagination than we do.”
