Astronomers hunting for alien life are sifting through the stars of our Galaxy like a chef sorting tomatoes for sauce. They reject based on simple signs: massive ones burn out too fast, young ones don't give life time to evolve, and without building blocks (heavy elements) you can't mold an Earth-like planet. Flares, especially from red dwarfs, and tight binaries create a killer climate. Chemistry is read from spectral lines, and stellar wobbles caught via photometry.

The trickiest filter is age. Instead of a precise number (which is almost impossible to know), they use an upper limit: if a star could be old enough, it stays. This saved 355,000 stars — more than any other criterion except the top two. After the sift, from 1.7 million contenders, 778,000 remained, mostly twins of our Sun. So many that any telescope, like James Webb, always has a suitable target to hunt for planet atmospheres through transit observations.