Imagine you’re a Trogdorian, living on the planet Trogdor seventy-five light years from Earth. It is ninety million years ago, and your planet has just developed the technology to survey nearby worlds for signs of life.

You train your ultra-sensitive space telescope on a pretty solar system with a yellow star and eight smaller worlds stretched out like gemstones on a necklace. One of these worlds, third from its star, lies at a distance where liquid water might exist on its surface. Intrigued, you set your spectroscope to examine the atmosphere (if any) of this orbiting rock.