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Adenine, cytosine, guanine, thymine and uracil. Those are the five ‘primary nucleobases’, the ‘letters’ (A, C, G, T, and U) whose multiple combinations make up life’s instruction book. The first four molecules ‘write’ our DNA, while the last (uracil) is only present in RNA, where it substitutes for thymine.
For decades, astronomers have toyed with the idea of panspermia, the theory that life, or at least its essential elements, did not originate on Earth but came to our planet aboard meteorites. And although scientists have already found numerous organic compounds and molecules in these space rocks, so far they had only managed to identify three of the five primary nucleobases, namely adenine, guanine and uracil.