The idea that Earth is unique in the universe by harbouring life is perhaps the ultimate question. And the search for alien life is now shifting from the realm of science-fiction to serious scientific discussion. This is because a recent succession of remarkable discoveries has made put the idea of alien life existing into the mainstream.
Dr Cathal O’Connell, of the University of Melbourne, believes “discovery of alien life now seems inevitable and possibly imminent.”
He said: “While life is a special kind of complex chemistry, the elements involved are nothing special: carbon, hydrogen, oxygen and so on are among the most abundant elements in the universe.
“Complex organic chemistry is surprisingly common. Amino acids, just like those that make up every protein in our bodies, have been found in the tails of comets.
“There are other organic compounds in Martian soil and 6,500 light years away a giant cloud of space alcohol floats among the stars.”
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The first planet beyond the solar system was discovered in 1995 and astronomers have since then catalogued thousands more.
Astronomers have consequently calculated there could be as many as 40 billion Earth-sized exoplanets in so-called “goldilocks zones”, where temperatures are mild enough to be potentially habitable.
For example, there is even a Earth-like world orbiting our nearest neighbouring star, Proxima Centauri.
At just four light years away, this planet is potentially close enough for mankind to reach using next-generation technology.
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Dr O’Connell said: “It seems inevitable other life is out there, especially considering that life appeared on Earth so soon after the planet was formed.
“Our planet was inhabited as soon as it was habitable – and the definition of ‘habitable’ has proven to be a rather flexible concept too.
“Life survives in all manner of environments that seem hellish to us.
“Tantalisingly, some of these conditions seem to be duplicated elsewhere in the Solar System.”
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Is there life elsewhere in our solar system?
Mars was once a warm and wet planet and potentially a fertile ground for life before the Earth.
And Dr O’Connell believes Mars still retains liquid water underground.
Methane, the gas associated with life on Earth, has been detected in the Martian atmosphere, with levels rising and falling with the seasons.
Dr O’Connell said: “Martian bugs might turn up as soon as 2021 when the ExoMars rover Rosalind Franklin will hunt for them with a two-metre drill.”
Besides Earth and Mars, at least two other places in our Solar System might be inhabited.
Jupiter’s moon Europa and Saturn’s moon Enceladus are both frozen ice worlds, but the gravity of their colossal planets is enough to churn up their insides, melting water to create vast subglacial seas.
In 2017, specialists in sea ice from the University of Tasmania concluded that some Antarctic microbes could feasibly survive on these worlds.
Both Europa and Enceladus have undersea hydrothermal vents, just like those on Earth where life may have originated.