Well, it sure is quiet around here. Our astronomical neighbourhood is very much a sleepy suburb on the outskirts of the stellar conurbation that is the Milky Way galaxy, our quiet corner of the cosmos is mostly inhabited by middle-aged stars like our Sun and their teenage planetary families. Few stars are born out here in galactic suburbia, and a few are close to death.
So far, Earth is the only planet we are aware of that harbours life of any kind. That does not necessarily mean that life does not exist on other planets, only that we have yet to discover conclusive proof of its existence. What does this apparent isolation tell us about the Earth? Is it possible to infer that our planet’s orbital, geophysical or astronomical environment is in some way unique or especially conducive to the synthesis of precursor proteins essential for life?
Upon considering these questions, a fundamental limitation presents itself. At present our catalogue of known extra-solar planets is populated by an ever-growing 562 members in 471 star systems. Due to limitations in contemporary astronomical technology and survey capabilities, none of these planets appear to be suitable proxies for Earth; most being too large or too far from their parent star. Smaller, Earth-sized planets are difficult to detect using the indirect methods currently employed by astronomers carrying out exoplanet surveys but improving observational technology may resolve these issues in the near-future.
However, this means that at present we have a sample size for life-harbouring planets of n=1, and as any statistician will tell you this is a very unrepresentative sample indeed. Therefore, it is difficult to infer any meaningful conclusion regarding the likely distribution of life in the Universe based on just this one planet. However, our insatiable curiosity tends to require us to make this assumption and this unfortunate circumstance gives rise to the many guises of the anthropic principal. The universe is as it is because we observe it to be so; if conditions in our solar system had been slightly different we may never have evolved the intelligence required to develop sentience and ask questions pertaining to our existence in time and space in the first place. All of our conclusions as to the nature of the universe have to be compatible with the life currently known to exist within it. As products of our astronomical environment, our existence remains permanently and irreconcilably incorporated into the logical framework of our understanding.
To most people, the fact that we have no discovered life on other planets is not surprising. Philosophy and religion have constructed elaborate logical mechanisms to explain our apparent isolation and confirm our fundamental, almost universal centrality and importance as an intelligent species. However, given the fact that there are possibly 1024 stars in the observable universe, it is certainly a statistical possibility that another Earth-like planet exists somewhere out there and that intelligent life may be flourishing elsewhere in the vastness of the cosmos. At least there is no reason, be it physical or chemical, it shouldn’t be possible.
Again, however, our sampling bias presents us with another problem; our entire understanding of life is formulated by studying that which exists on the Earth. The molecular backbone of terrestrial biochemistry is based on carbon and the effectiveness of liquid water as a solvent, and we therefore assume, not unreasonably given the ubiquity of water and carbon compounds in space, that is will be the likely form that extraterrestrial life will take. It is hypothetically possible however, that other forms of biochemistry may exist to exploit different planetary environments, using different solvents and electron donors, or operating on a spatial or temporal scale that would be difficult to reconcile with our understanding of life.
However, it is also equally possible that we are in fact the only intelligent life ever to have emerged in the temporal and/or spatial dimension that we inhabit; the evolution of our superlative intellect may only possible under very limited, serendipitous and fortunate circumstances, the kind of which has never arisen on any other planet in the past. The evolution of simple life may be a relatively easy step; intelligence however may be another matter. We may therefore be sole custodians of the meaning of life, even if we haven’t uncovered it yet. In this case we have an enormous responsibility to protect and preserve our planet for future generations who may be better equipped technologically to answer these fundamental questions regarding our existence and uncover the deep-seated meaning embedded in our seemingly chaotic existence.