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Richard Webb
Tribune News Service
1 Martian canals
The idea of channels extending die-straight over the surface of Mars is the granddaddy of alien conspiracy theories. The idea that vast ditches, first described by Italian astronomer Giovanni Schiaparelli in 1877, irrigated a Martian civilisation was championed by the US entrepreneur and astronomer Percival Lowell, and persisted for decades.
Modern-day high-resolution imaging reveals any canals to be, at best, transient phenomena perhaps streaks of dust caught in the lee of mountain ranges and craters in Mars's relatively feeble winds.
2 Flickering stars
One sure-fire way to attract the attention of the outside world is to flick the lights on and off. That's what happened when an otherwise unremarkable star, hitherto known as KIC 8462852, was seen to dim repeatedly and irregularly over several days in 2015.
The star was quickly redubbed Tabby's star, after the lead author on the paper detailing the finding, Tabetha Boyajian of Yale University. Since then, the Kepler telescope has shown that the star's brightness, besides the dips, also declined over a period of years, first slowly, then more quickly an inexplicable pattern that fuelled speculation it could be hosting a vast alien construction project.
Or not. Detailed readings published last month indicate that the star's light isn't dimming equally at all wavelengths, ruling out light being blocked by an orbiting alien megastructure. It seems more likely that vast swirling clouds of dust, probably produced by passing comets and asteroids, obscure the view and account for this odd stellar behaviour.
3 Gamma-ray bursts
The US Department of Defense's Vela satellites were designed to pick up signs of illicit nuclear weapons tests in the 1960s. But starting in 1967, they picked up powerful blasts of gamma-ray radiation coming from outer space.
The findings were only declassified in 1973, exciting speculation of conflict in galaxies far, far away. But as we've observed more gamma-ray bursts, and more closely, over the past decades, we've come to realise they are probably not one phenomenon. They are several, entirely natural ones originating when massive stars collapse during a supernova to form a neutron star or black hole, or when two neutron stars collide.
4 Pulsars
1967 was a good year for would-be alien hunters. That's when Jocelyn Bell Burnell and her collaborators picked up a metronomically repeating signal in their radio antenna. It certainly came from nowhere on Earth, and the astronomers jokingly dubbed the signal"Little Green Men 1". Predictably, when they inserted a line about briefly considering an alien origin into the paper describing their finding, it unleashed a media storm. It was in fact a pulsar, a rapidly rotating, incredibly dense neutron star. Thousands have since been discovered, their regular pulses making them among the most precise clocks in the universe.
5 The Wow! signal
The Big Ear programme at Ohio State University, which ran from 1973 to 1995, used a radio telescope the size of three American football fields to listen for signs of ET phoning other people's homes. On 15 August 1977, it picked up a powerful burst of radio waves, lasting 72 seconds, from the constellation Sagittarius. It was at very close to 1420 megahertz, a frequency naturally emitted by hydrogen in space, which is therefore considered a likely conduit for alien messages.
When astronomer Jerry Ehman saw the signal recorded on a computer printout, he circled it in red pen and scrawled"Wow!". But despite extensive searches of the patch of sky the signal came from, it has never been seen since. In recent years, scientists have speculated that freak interference from two passing comets could have caused it.
6 Fast radio bursts
If the Wow! signal was wow, the first fast radio burst was even wow-er. Seen in 2007 by astronomers at West Virginia University, it lasted for just 5 milliseconds, but released more energy than the sun emits in a month.
Dozens more of these signals, apparently originating outside our galaxy, have since been detected. In 2017, astronomers Manasvi Lingam and Avi Loeb at Harvard University speculated they could be radio beams used by alien civilisations as beacons or to power spacecraft.
Such ideas are nourished by the oddest fast radio burst of all. First spotted in 2012, it has been found to repeat 15 times in just one survey done in 2017 by the Breakthrough Listen project, which looks for signs of alien intelligence. The latest measurements, however, suggest it is the product of a neutron star rotating in the magnetic field of a huge black hole.
7 Our genomes
In the absence of a smoking gun from the sky, committed alien hunters often look for signs closer to home. For some it is crop circles, but around a decade ago a slightly more serious idea began to circulate: that alien messages might be encoded in our DNA. As Paul Davies, author of The Eerie Silence: Renewing our search for alien intelligence, asked in New Scientist in 2004:"Might ET have inserted a message into the genomes of terrestrial organisms, perhaps by delivering carefully crafted viruses in tiny space probes to infect host cells with message-laden DNA?"
In 2013, the idea was revived in a slightly different form. A pair of Kazakh researchers claimed to have found"the Wow! signal of the genetic code" in the form of a series of patterns that all seem to revolve around the number 37. The idea was"not, in and of itself, absurd", as one expert contacted by New Scientist at the time summed up. But then again, if you want to see aliens, you will see them anywhere.
