A planetary scientist, Johnson is passionate about searching for life in unlikely places—whether that means an isolated Australian lake “stippled with halite, a…table salt,” above the cloud line on a Hawaiian volcano—or on Mars. Hopes for life on the red planet have always been high, with early observers mistaking Martian dust for vegetation and even elaborate civic projects. Yet as more sophisticated explorations have exposed these as fictions, actual pictures of that red dust have produced evidence that the conditions to support life really did exist there once. As she traces the challenges, findings, and failures of a string of Surveyors, Rovers, and Explorers, Johnson’s meticulous and lyrical descriptions (the sky on Mars, for instance, isn’t black or blue but butterscotch) convey not only the science but the human quest for meaning that’s driven the work—despite the fact that “half the missions to Mars have failed”; Johnson’s own engagement in this endeavor has been so deep that her first child was due on the same day the Curiosity was scheduled to land on Mars, giving added oomph to her conviction that these missions represent “an almost existential endeavor…to learn what life really is.”