As we become more advanced in astronomy, continuously searching and finding lots of potentially habitable extrasolar planets that could harbor alien life, it seems that it’s not a matter of if but when we will find extraterrestrial organisms. However, the real tough problem here is: How we could determine if the alien life has really been found? “The question is not so much ‘when will we find extraterrestrial life?’ But ‘when will we know we have found extraterrestrial life?'” Terence Kee, the President of the Astrobiology Society of Britain told Phys.org. “My feeling is that we may indeed find signs of life in a few decades, but whether we will be unambiguously able to identify it as ‘extraterrestrial life’ – as opposed to terrestrial contamination or abiotic far-from-equilibrium processes – in such a short time-frame, I’m not so sure.”
Kee noted that we are able in any realistic sense to detect only life forms that have a terrestrial-based biochemistry, so we would probably bet on bodies that have liquid water and some form of geological free energy source. He puts his hopes on space probes looking at out-of-equilibrium gas distributions in exo-planetary atmospheres. However, any potential findings revealed by these probes would be only an indication, without the capability to definitively determine the existence of alien lifeforms.
We could also turn to meteorites in the ongoing search for E.T. . . .