Until last fall Amber Young was a NASA astrobiologist seeking signs of life on the more than 6,000 planets discovered beyond our solar system. She is fascinated by exoplanetary atmospheres and the signatures in them that offer clues that organisms might exist somewhere on those worlds. “Life changes the atmosphere,” she says. Now in her new role as a NASA project scientist, she calls shifts in atmospheric composition “the loudest way” life makes its presence known. Even though she’s not...