First discovered in 2015 by the Kepler Space Telescope, K2-18b quickly drew attention. It is roughly 2.6 times Earth’s diameter, making it unlike anything in our solar system—a so-called “hycean” world. Imagine a planet with a deep, global ocean beneath a huge, puffy atmosphere dominated by hydrogen and helium. It’s not unlike Lewis’ fictional world Perelandra: vast, watery, mysterious.…
