With a slew of new missions poised to return data from alien worlds, the pace of these potential discoveries is likely to accelerate. So, what questions should we ask ourselves when apparent evidence of alien life inevitably arrives? In this guide, we’ll walk through the most plausible ways it might first show up, from faint chemical signatures to fossilised microbes. Think of it as a scientific gut-check – a sliding scale of how close different scenarios come to proving alien life exists next time headlines proclaim we’re not alone.