In the coming decades, our ability to find and catalogue exoplanets within our own galaxy will improve exponentially and although direct observation may well be impossible, we will be able to measure the exact composition of a distant planet’s atmosphere by analysing the light that has reached us. From this, several things follow.
The composition of an atmosphere should tell us if it can sustain life – certainly the kind of life that we are used to: carbon based life that requires liquid water. Also, the composition of the atmosphere will contain tell tale chemical signals of life within the biosphere and at what stage that life is at. Very detailed analyses have been made of the Earth’s atmosphere through out different historical epochs and these can be compared to exoplanet data. If the life forms within the biosphere of an exoplanet have reached a civilised state, then any artificially created elements or exotic molecules will also be detectable. The statistical analysis of this data should prove beyond a shadow of a doubt if life exists elsewhere in the universe, and there will be shouting in the streets of planet Earth.
There is a downside. It is probable that any exoplanet with the correct fingerprint for life, will be so far away that all life on the planet may be extinct. Exoplanets that show life in it’s early stages may give enough data for us to make a tantalizing guess at what level that life has reached by the time it’s light has reached us. However we will never know for sure if it evolved into intelligent species.
We will only ever be able to witness the ghosts of life.
– Your Joyful Benefactor