Scientific American Meet the Unsung Heroes behind Humanity’s Improbable Journey to an Alien Ocean The author of a new book reveals the hidden human history of NASA’s in-development Europa Clipper mission Print Artist’s concept of NASA’s Europa Clipper mission at Jupiter’s moon. Credit: NASA and JPL-Caltech Advertisement Recent headlines aside, NASA’s most exciting interplanetary mission for the early 21st century is arguably not a robot named Perseverance presently roving around Mars gathering samples for a future return to Earth. Instead it is a spacecraft, just now on the verge of being built, that could launch later this decade to Europa, an enigmatic moon of Jupiter that boasts an enormous ocean—bigger than all of Earth’s oceans combined—beneath an icy crust. Called Europa Clipper, the mission could lift off as soon as 2024 to study the moon’s subsurface abyss with the goal of gauging its potential habitability and the distinct possibility of discovering a “second genesis” there. Many astrobiologists consider Mars to be a prime target for seeking out signs of ancient, now extinct extraterrestrial life because of its relatively Earth-like conditions billions of years ago. Europa, by contrast, has never really been like Earth at all, but it still may offer the solar system’s best prospects for harboring alien organisms that are alive