When, in the mid-16th century, Nicolaus Copernicus corrected more than a millennium of geocentric folly by reestablishing that the Sun, not the Earth, was the centre of our solar system, the Polish astronomer illustrated a cosmological notion that now bears his name.
The Copernican principle generally dictates that we are not special. It is humbling, but true: the history of our galaxy, of our planet, of our species and so on – these are more likely ordinary than exceptional.
The discovery of seven Earth-like planets in a solar system not so far away should therefore come as no great shock. Yet the find, published in the scientific journal Nature this week, is captivating because of its promise. As Amaury H.M.J. Triaud, a member of the international research team that discovered the planets, said, “I think that we have made a crucial step toward finding if there is life out there.”
The Copernican principle is often invoked by the growing group of serious scientists who believe that Earth is probably not the only planet able to sustain life and that we are not alone. After all, it is thought there are more planets in the universe than grains of sand on Earth. “To declare that Earth must be the only planet in the cosmos with life would be inexcusably egocentric of us,” the physicist Neil deGrasse Tyson wrote in 2003.
Still, of the nearly 3,500 so-called exoplanets astronomers have so far found beyond our solar system, very few have the characteristics necessary to host life. That’s why the discovery of the planetary system known as Trappist-1 has caused such a stir. At least three of its planets lie in the so-called Goldilocks zone, where surface temperatures are neither too hot nor too cold, ranging from 0 to 100 degrees Celsius, and the conditions are just right for watery oceans.
Life would also be rather scenic, a cinematographer’s dream. So dim is the star at the centre of the system that the planets are believed to be bathed in a constant twilight. So crowded are the planets around their star that if you stood on the surface of one, the others would loom in its sky larger than the moon does in ours.
That we can assert with confidence so much about a septet of planets 235 trillion miles away is a profound testament to human ingenuity and the otherworldly power of science. It will take much more of the same to answer the fundamental question raised anew by their discovery: are we alone in the universe?
Scientists will now use telescopes to search for gases such as oxygen, ozone and methane that would indicate the presence of life in Trappist-1, a project that will likely take around five years. If no signs are found, the question will be why planets so much like ours did not yield life as Earth did. If, on the other hand, such gases are found, the next question will be much more interesting: what might our intergalactic neighbours be like?
It is essentially human to wonder about our place in the universe and whether we are alone. But as the Copernican principle and the newly discovered planetary system remind us, what is essential to us may not be unique to us. Are we alone? Perhaps not even in our greater celestial neighbourhood. Who knows, perhaps not even in wondering.
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