The Hunt for Life on a Moon of Jupiter Begins - Nearly half a billion miles from Earth, a world may be stirring.

Europa has fascinated astronomers and exobiologists at least since 1979, when the Voyager 1 and 2 spacecraft reconnoitered the moon and photographed an icy white surface shot through with cracks and fractures, suggesting a churning ocean disrupting the frozen crust. The later Galileo mission, which orbited Jupiter from 1995 to 2003, discovered that Jupiter's magnetic field is disrupted in the vicinity of Europa in a way consistent with a deep, electrically conductive liquid beneath the surface of the moon. The Juno mission, which has been orbiting Jupiter since 2016, has been studying Europa more closely still, documenting ice walls, scarps, and ridges, all pointing to a surface in constant motion. Astronomers now believe that Europa has an ice shell up to 15 miles thick, covering a global ocean up to 100 miles deep.

- By Jeffrey Kluger

Our planet is the only one on which we know life exists. But if the basic sciences of chemistry, energy, and biology apply, Jupiter's moon Europa may be alive as well. NASA aims to start finding out, with the October launch of the $5 billion Europa Clipper spacecraft on a 5-year journey to the Jovian system for the most detailed exploration ever of the mysterious icy moon.