The idea that there might be other beings in the sky has been with us for centuries. Earthlings have always gazed at the heavens and wondered about the presumed builders and occupiers of the vaulted heavens: the gods, spirits, angels, and demons who were, so to say, the first extra-terrestrials.

The notion found its first roots in Greece. As early as the fifth century, the Thracian philosopher Leucippus and his pupil Metrodorus of Chios wrote that: “It seems absurd, that in a large field only one stalk should grow, and that in an infinite space only one world exists.”

Sceptics existed too. Both Plato and Aristotle lambasted Democritus’s idea of a plurality of worlds on theological grounds. Plato, a monotheist, argued that there is only one creator and that therefore there can be only one world. So did Aristotle who, though he was a pagan, posited a picture of the universe that was a gift to early Christian theologians.

The Book of Genesis excluded other worlds or other sentient beings, asserting that God purposefully created the heavens and the earth. The New Testament then expanded the idea by positing that God was incarnated as Christ to rescue the faithful from sin and damnation. As the scientist and Christian apologist William Whewell would later put it, the Incarnation made Earth into “the Stage of the Great Drama of God’s Mercy and Man’s Salvation”, a flattering story implying that humans are uniquely worthy of Christ’s sacrifice.

Nicolaus Copernicus is central to the story of extra-terrestrials, not because the Polish mathematician and astronomer believed in them, but because he was the first person to propose, based on observation and calculation, that Earth was not the centre of the visible universe.

His follower Giordano Bruno, a Dominican friar who became a religious vagabond, read Lucretius and Copernicus, took their ideas deeply to heart, and made some startling leaps of his own. In three sets of dialogues published between 1584 and 1591, Bruno argued that at least some of the stars are suns with their own planets and that some of these planets must have their own residents.

The idea that there might be other beings in the sky has been with us for centuries.

Bruno’s audacious views conflicted with long-standing doctrines of the Catholic Church. He was arrested in Venice in 1592 on charges of blasphemy and heresy. His trial in Rome lasted seven years, culminating in his being hanged naked upside down and burned at the stake.

In 1609, Johannes Kepler, the German mathematician and astronomer, published Astronomia Nova (“New Astronomy”), which extended Copernicanism in crucial ways. Soon after, Kepler sent Galileo a letter that included speculation about extra-terrestrials. Any planet important enough to have moons, Kepler presumed, must also have people.

Not surprisingly, it took a Frenchman named Bernard le Bovier de Fontenelle to exploit the subject’s humorous possibilities. His 1686 book Entretiens sur la pluralité des mondes(“Conversations on the Plurality of Worlds”) was an early example of science popularisation.

Fontenelle used fanciful proto-science-fiction notions about the cultures of the other planets. The people of Venus, Fontenelle mused, are “sunburnt, full of verve, always amorous, loving verses, loving music, inventing celebrations, dances, and tournaments every day”, probably the forebears of today’s Italians. The inhabitants of Saturn, by contrast, are “quite phlegmatic. … These are people who don’t know what it is to laugh, who always take a day to answer the slightest question asked them”, surely the ancestors of today’s Germans. 

And then, what about the people of Mercury?  Fontenelle speculates that they are “so full of fire, they are absolutely mad and have no memory at all …  they make no reflections, and what they do is by sudden starts, and perfect hap-hazard: in short they exist in a Bedlam of the universe”. No doubt, they must be the forerunners of today’s Maltese.

1897. G. Wells took Percival Lowell’s concept of an ancient, advanced race of Mars dwellers and added a layer of malice in The War of the Worlds, which was published in serial form in 1897. Orson Welles adapted H. G. Wells’s story as a live radio drama broadcast on Halloween Eve in 1938. Its simulated news format scared quite a few listeners into believing invaders from Mars had really arrived. Today we know that Mars is cold and dry and that if there is life, it is probably microbes buried below the surface.

In the 1940s and 50s reports of “flying saucers” became an American cultural phenomenon. Sightings of strange objects in the sky were transformed by Hollywood into films about potential threats. Even today, millions of people wonder where the extra-terrestrials on UFOs are coming from, or whether they are watching us.

After all, astronomers have drawn up lists of nearby star systems where any inquisitive inhabitants on orbiting planets would be well placed to spot life on Earth. The scientists have identified 1,715 star systems in our cosmic neighbourhood where aliens could have watched Earth “transit” across the face of the sun over the past 5000 years.

The researchers estimate that 29 potentially habitable planets are well positioned to witness an Earth transit and eavesdrop on human radio and television transmissions. One star 11 light years away, known as Ross 128, a red dwarf in the Virgo constellation, has a planet nearly twice the size of Earth.  

Another star called Trappist-1 is also close enough, at 45 light years, to eavesdrop on human broadcasts. The star hosts at least seven planets, four of them in the temperate, habitable zone, but they will not be in position to witness an Earth transit for another 1,642 years, scientists write in Nature.

In the Asteroid Belt between Mars and Jupiter, scientists have noted there appears to be a missing planet. The asteroid belt could have been formed by an exploding planet. Could we be descendants of an alien race who escaped just before the explosion?  

Environmentalist and ecologist turned author Dr. Ellis Silver believes this is the case. In his book, Humans are not from Earth: A Scientific Evaluation of the Evidence, Dr. Silver presents 17 reasons why humans are not suited for living on this planet. He believes these reasons indicate we originated from another planet.

For example, he states that humans do not do well with large doses of sunlight, which we receive every day. He also remarks about the large number of people in the world who have chronic back aches, which he attributes to evidence that we originated from a planet with lower gravity. According to him, we are better programmed to exist with a 25-hour day instead of a 24-hour one.

Silver suggests we may be the descendants of aliens from Alpha Centauri. If aliens were to visit us again, who could protect us? The Men in Black? I doubt that a veteran lawyer (Tommy Lee Jones) and a fish-out-of-water recruit (Will Smith) would be up to the task.