Last fall, astrobiologist Kevin Hand and I were aboard the Norwegian icebreaker Kronprins Haakon for a month, crashing through the frozen ocean off the northeast coast of Greenland. Around us, Earth looked alien—a world where the normally shifting seas were a solid mass of glowing ice.

The otherworldly environment was fitting for the expedition, which had been dispatched to this frigid place to hunt for signs of life in the deep that might resemble organisms on other worlds, including the icy moons of the outer solar system. Some of these moons—particularly Europa, Titan, and Enceladus—are considered the best places to look for life beyond Earth.

In the mid-2020s, NASA plans to launch a spacecraft to Europa, one of Jupiter’s