What are the chances of life existing in other solar systems?
The probability of life depends, primarily, on your point of view of what constitutes ‘life’. If we consider life as carbon-based, like life on planet Earth (a good assumption as, while other forms of life may exist, they are likely to be highly different from us and so communtication with them may be impossible – indeed we may not even recognise them as life forms. This is why you may hear many people talking on the subject referring to life ‘like us’.) the main arguments rest on the local environment of the planet, and the likelyhood of primordial life on a suitable planet forming. For a planet to have a good chance of beaing able to support life, it must be located at quite a precise distance from it’s local star. Earth is located within this ‘temperate zone’ in our solar system, and Mars is just at the edge of it. Aside from that it’s orbit must be stable (no long winters or baking summers). Water must be able to exist on the planet in a liquid state (this is why there is some spec
http://www.columbia.edu/cu/augustine/arch/frear/rutler97.htm Shows the equation for the chances of life on other planets as N = R Fp Ne Fl Fi Fc L The problem is that it relies on our interpretation of what constitutes life, and depending on our answer shows that it’s either almost impossible or almost certain that life exists out there somewhere. I plump for the idea that there IS life somewhere, but perhaps not how we would like to think of life, simply because there are around 7 sextillion stars in the universe, and if we are even a one in a billion chance of life then that makes 70 thousand billion instances of life around.
