Most of us have looked up at the sky in the middle of night.
Most of us have looked up at the sky in the middle of night. We’ve looked at the seemingly endless blanket of stars above our heads and asked ourselves perhaps the most important question that our species has yet to find an answer for. Are we alone out there?
There is so much that we can see in the sky at night, and yet it is barely a fraction of what exists beyond the reach of our naked eye or even our most powerful ground based telescopes. Even the telescopes we have in orbit around our planet, and the more sophisticated ones that we intend to launch within the decade, will not be able to observe in detail a millionth of what lies beyond our atmosphere.
Our planet is one of eight in our system. Our system orbits one star – the Sun. The number of exoplanets, planets outside our system that is, is confirmed to be at least 1796, with new ones being discovered all the time.
Estimates suggest that there are around one hundred billion stars in our galaxy, the Milky Way. However it is estimated that there are around one hundred billion planets in the galaxy, roughly one per star.
Of course not every star has planets, and some stars will have multiple planets. We know of at least 461 stars with more than one planet orbiting them. Currently we know of two stars with seven planets orbiting them – and one of those, named HD10180, is believed to have two more unconfirmed planets in its orbit.
Despite its immeasurable size, it would take one hundred thousand light years for light to cross it, the Milky Way is but one of an estimated one hundred billion galaxies in our observable universe.
Those are numbers that no human can ever hope to even come close to understanding.
Of course not every planet is inhabitable by life as we know it. Due to our current technology and methods for detecting exoplanets most of those that we find are gas giants – similar to Jupiter or Saturn – and obviously completely hostile to life such as our own.
We also find rocky planets like our own. But again they are not necessarily welcoming to life. We on Earth are lucky as our planet orbits in what is known as the goldilocks zone. We are just far away enough from our star to have liquid water on our surface, unlike Venus which lost its oceans aeons ago, but close enough for it not to freeze as is the case with the ice caps on Mars.
There are other factors that we believe were critical to the creation of life on Earth aside from liquid water on the surface. Things such as an atmosphere, oxygen, plate tectonics and a myriad of other factors that came together to allow life to flourish on Earth.
An intelligent civilisation
As for what we could consider intelligent life then again we got lucky. Life existed on Earth for billions of years before we showed up. It took a chance meteor impact to wipe out the dinosaurs and allow us mammals to come to rule the Earth.
Even now, of all the millions of species that still exist on Earth today, there is only one that can read what I have written here. Us, and even then only a percentage of “us” can.
The Drake equation, proposed in the 1960’s suggested that we took the number of stars in our galaxy, rounded them down to a tiny percentage to those that may have planets, then did the same for the amount of those planets that could support life, the same for those that could support intelligent life, the amount of those that could release signs of their existence into space and the length of time those species could do so.
The result is still tens of thousands of intelligent civilisations across the Universe, regardless of how small you make the numbers.
It is a question to which the answer can never be “no.” We will never have the capacity to scan for life every star, planet, asteroid, comet and meteor in our own galaxy, let alone the countless billions that lie beyond. Either we find life elsewhere or we never know. The answer is never “no, we know there is no one else”
Myself, I’m an optimist. There are thousands of reasons we’ve not heard or detected them. For all we know the planets two star systems over could be teaming with life – but nothing intelligent enough to signal or send messages we could detect.
The star system beyond that could have been ruled by a space-faring race that ruled their system for ten million years. They could have died out due to a myriad of reasons. For all we know their last transmission passed by our planet ten seconds before we started searching for alien radio signals – and we’ll never know they were there.
There are countless reasons we’ve not found them, and that is something I intend to go into in the future. But there is just one more thing to say.
Everything I’ve said so far has been based on life as we know it. For all we know the Universe is full of life as we don’t know it.
What do you think? Have your say in the comments section below.
Image: ESO / Wikimedia Commons