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.