A nearby exoplanet orbiting within the habitable zone of a star just 4.2 light-years from Earth may be home to a vast ocean, boosting its chances of supporting life. Since its discovery, questions about the conditions at the surface of Proxima b have been swirling; the planet’s mass is just about 1.3 times that of Earth’s, and the red dwarf star it circles is similar in age to our sun. Studies over the last few years, however, have both bolstered hopes of its habitability and shot them down. Now, a new study has once again raised the possibility that Proxima...