Europa, Jupiter's ice-cloaked ocean moon, contains far less oxygen than previously thought, making it a poor candidate for sustaining alien life. This number is far lower than previous computer model predictions, which estimated the surface produced 2,205 pounds (1,000 kg) of oxygen per second. But scientists remain optimistic that Jupiter's fourth largest moon, which is perhaps best known for having an underground ocean, could still harbor life in the form of microbes.