It is a fascinating question for mankind and no better summed-up than by Arthur C Clarke when he said: “Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.”
Currently there is no evidence for life beyond the earth. This does not stop us speculating and indeed spending billions of dollars searching.
Conditions for Life
Assuming we can rule out “It’s life Jim, but not as we know it” – then there are some basic requirements for life to develop on another planet. I am not a biologist so I hope you will forgive me if I do not define ‘life’ – particularly as what constitutes life is debated in the scientific community.
The four key ingredients to enable life are: water – within the temperature range so that it is not permanently frozen or vaporised. The second is the chemical element used in the building blocks of all types of life and that is carbon. The third is energy gradient, and this may come from chemical reactions or a star or from seismic activity within a planet’s core. The fourth is some form of nutrients to maintain the life.
You may also argue there is another key factor and that is time. To put this in perspective, primitive life emerged within a few hundred million years of earth’s formation. It developed once the bombardment ceased and oceans formed. Had the conditions changed during that early period, then life may never have flourished.
The earth is around 4.5 billion years old. To go from single cell life to homo sapiens took some time as homo sapiens has only been around for the past few hundred thousand years.
Where could we find life?
The Solar System?
It has always been speculated that Mars has harboured simple life. Many robotic missions have been sent to our neighbouring planet to sniff, photograph and dig our way around. There is evidence that water flowed on Mars, plus carbon-based molecules have been detected. The planet is pretty inhospitable but not so extreme that in its history it could not have enabled simple life to develop. I think one day we will find evidence for simple life having existed on Mars. (Although Bowie said – It’s a God-awful small affair).
Most of the planets in our solar system have moons; some have as many as 80! There is strong evidence that some of the larger moons, such as Saturn’s Titan and Enceladus have sub surface oceans. Maybe these could support life? It will take many decades before we are able to land and dig a few kilometres below the surface. In the meantime we continue to send missions to planets, moons and comets within our solar system looking for evidence for the right conditions for life to have formed.
In deep space?
We live on a planet orbiting an average star within what is called a galaxy – a swirling mass of stars and dust. In our galaxy there are hundreds of billions of stars: some smaller, some larger, some hotter, some cooler, than our Sun. We now know that within the universe there are tens of billions of galaxies, each galaxy with their own hundreds of billions of stars. So there are billions of trillions of stars in the universe.
Then a mere 25 years ago we made a remarkable discovery. We detected a planet orbiting another star: called an exo-planet. Since then we have discovered many thousands of exo-planets orbiting stars in our galaxy. So other stars have ‘Solar Systems,’ like our sun, with numbers of planets in orbit.
It is now postulated that most stars have these planetary systems. So if there are billions of trillions of stars and most have numbers of planets and many of those planets have moons, then you may argue there has got to be life out there!
Well, maybe. A large proportion can be ruled out due to extreme temperature or radiation. Or maybe the star they orbit has a short life-span so life on the planets never gets established or is destroyed.
In 2021 NASA will launch the long overdue James Webb Space Telescope. This will search for more exo planets, particularly those whose orbit around their host star ensures they are not too hot and not too cold – this is known as the ‘Goldilocks zone’. Of course the Earth is in a Goldilocks zone!
This space telescope will also detect the constituent chemicals of exo planet atmospheres. So we will be able to see if carbon-based elements exist and crucially, if there is water in the atmosphere.
Imagine too if we detected a gas within an exo planet atmosphere: one that cannot be formed by nature alone– such as the fluro-carbons that exist with our own planet’s atmosphere – man made. That would be a tell-tale sign that a sophisticated life form existed on that planet – at some time. How exciting that would be!
In addition to the space telescopes, we also have the SETI project (Search for Extra Terrestrial Intelligence). This scans the heavens for unusual signals – ones that do not occur naturally our have a specific pattern that could only be created by a life form. Nothing yet!
With all these planets and with all this searching why haven’t we found anything yet? The universe has been around 14 billion years: ample time for unimaginably advanced life forms to populate all corners of the universe, surely? Think for a moment – Mankind has only been around a few hundred thousand years – yet we have already sent spacecraft beyond our Solar System. Surely within a few hundred thousand years we will have sent humans to other stars and planets in deep space? What about in a few million years’ time -would we not be spread across the universe?
If this is a reasonable assumption, then why have we not seen evidence for advanced life – life that have been around for millions or billions of years and can populate far afield from their home?
I do not have the answer. But maybe, as life becomes highly advanced, it ultimately destroys itself with its technology. Not a nice thought. Or perhaps it morphs into a highly technologically advanced virtual world and never has the need to leave the home planet? Or maybe the answer is- there is no technology that enables long distance travel? We also make the assumption that other life forms have the in-built desire to investigate- to seek new things. Humans have always been pioneering – whether it was roaming to a new continent or setting sail across an ocean without knowing what they would fine.
So what about the question : ‘do you think there is alien life out there?’
I believe that within my lifetime we will detect ‘simple’ life somewhere else. That will be so incredibly exciting. I think we will find evidence for ‘simple’ life forms within our Solar System. This may not indicate that there is life further afield- outside of our Solar System – as it could have been seeded from the same source as that on Earth.
As for more sophisticated life, it is always going to be less likely as it is such a vast leap from simple life to multi-cellular life and then to Homo Sapiens. Many things can fail along the way.
On balance, I believe advanced life has existed in the history of the universe and may well exist now. But, and it is a big ‘but’ – in the relative vast time-span of the universe – maybe advanced life is relatively transient – so it never discovers another advanced life form – it destroys itself before it has the time or technology to find friends. That may be a good thing for us, who knows?