Last week, stories about an exoplanet with an intriguing atmosphere dominated my news feed. A team of scientists had found a signal attributed to a gas that on Earth comes from marine organisms. While the signal is compelling – University of Arizona astronomer Daniel Apai described it as “exciting” in the story he wrote for us – it’s not very strong. Without more data, it’s certainly not a smoking gun indicating alien life.

The more I read about what those scientists found, the more I couldn’t help but wonder what would qualify as bulletproof evidence for extraterrestrial life. Unless an alien spaceship touches down, confirming life on another planet probably won’t be a straightforward process. Luckily, Chris Impey, an astronomer at the University of Arizona, was happy to describe the steps that scientists take to make sure what they’re finding is actually a real discovery.

K2-18b doesn’t represent the first time researchers have found something that perhaps could indicate the presence of life on another planet. But in most cases, making too strong a claim about extraterrestrial life too early has gotten scientists burned when the evidence hasn’t backed them up. In his article, Impey describes three key criteria for major discoveries, with examples of scientific achievements that do and don’t stack up. A claim about alien life will have to meet these criteria before most scientists are ready to believe it, because as the adage goes, “extraordinary claims require extraordinary evidence.”

This week we also liked articles about whether leaders from one major political party or the other are better at reducing crime rates, the erosion of “boundaries between public governance and corporate surveillance,” and why dying people can defy the odds by staying alive for an experience they care deeply about.

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