Image of Keck Observatory
I've been thinking about sentient life in the Universe (as you do) and realised that, while I had all the facts in my brain,I had never really put them together in any meaningful way before.
Our planet sits in her orbit at a perfect distance from her sun, which is a perfect example of a star configured to give rise to - well - us.
I nearly said 'intelligent life' there for a minute.
There is a finite number of such stars in our galaxy and we are unaware for the most part whether they have attendant planets or not. But I don't see why they shouldn't have, so let's go with that assumption for the moment.
OK then- star in the Main Sequence of the Hertzsprung-Russel diagram, not too hot nor too cold (one of the G-sequences), not too young (life took about 4.5 billion years to arise here) , a T-type planet orbiting in the right zone not to fry or freeze life, having sufficient mass to retain an atmosphere (Mars and the moon are a tad too small).
It's not beyond the bounds of possibility that several planets with these precise specs exist, somewhere.
But consider- 65 million years ago, a bloody great comet sweeps in from the outer reaches of the solar system and boom all higher life forms are extinguished. Which at that time were the dinosaurs.
The chances are good that the Earth would be hit by such a massive comet or asteroid every few hundred thousand years if not for the presence of two large gaseous planets- Jupiter and Saturn.
That's right. The Emperor and the Grandfather are directly responsible for allowing our kind of life to arise upon the Earth. Thank you, Your Majesty. Thanks, Gramps.
But now take that thought and add this fact to it: large gaseous planets of the J-type are incredibly difficult to form from the disk of a growing star. Much more tricky than the little T-types,such as Mercury, Venus, Mars and Us.
So - are we a very uncommon phenomenon, rather than the norm?
Are there in fact no wiser races inhabiting the galaxy or even the universe?
Are we perhaps all alone?
I admit to finding this thought more than a little terrifying.
It's one thing to wonder how we'd shape up in some Galactic Council among more advanced races and another altogether to contemplate the possibility that there's no one out there at all.
Just us, alone in this huge universe.
What a responsibility.