NASA scientists say images taken by the Hubble Space Telescope in 2014 suggest there may be water vapor plumes erupting off the surface of Jupiter's moon Europa. WSJ's Monika Auger reports.

Europa, one of Jupiter’s intriguing moons, is hiding an ocean beneath its icy shell — an ocean that might harbor alien life.

Only some 60 million years old, Europa's brittle surface appears to be in constant flux. Energy-rich compounds there could reach the ocean as pieces of the crust slide under each other.