At long last, NASA's Europa Clipper mission is on its way. It launched on October 14 and is now en route to its target: Jupiter's ice-covered moon Europa, whose frozen shell almost certainly conceals a warm saltwater ocean. When the spacecraft gets there, it will conduct dozens of close flybys in order to determine what that ocean is like and, crucially, where it might be hospitable to life. Europa Clipper is still years away from its destination--it is not slated to reach the Jupiter system until 2030. But that hasn't stopped engineers and scientists from working on what would come next if the results are promising: a mission capable of finding evidence of life itself. Living as long as a thousand years, the American chestnut tree once dominated parts of the Eastern forest canopy, with many Native American nations relying on them for food.

This would likely have three parts: a lander, an autonomous ice-thawing robot, and some sort of self-navigating submersible. Indeed, several groups from multiple countries already have working prototypes of ice-diving robots and smart submersibles that they are set to test in Earth's own frigid landscapes, from Alaska to Antarctica, in the next few years But Earth's oceans are pale simulacra of Europa's extreme environment. To plumb the ocean of this Jovian moon, engineers must work out a way to get missions to survive a never-ending rain of radiation that fries electronic circuits. They must also plow through an ice shell that's at least twice as thick as Mount Everest is tall. "There are a lot of hard problems that push up right against the limits of what's possible," says Richard Camilli, an expert on autonomous robotic systems at the Woods Hole Oceanographic Institution's Deep Submergence Laboratory.