Europa's frozen, fissured surface, seen here in a colorized mosaic image from the Galileo spacecraft, hides a liquid ocean that may hold all the ingredients needed for life.
Three key ingredients are needed for life as we know it: essential elements like carbon, nitrogen, and sulfur; an energy source, and liquid water.
Europa's surface captures sulfur flung into space from its volcanic sister moon Io. Sulfur can be converted into a source of chemical energy for life.
Jupiter and moons not to scale
Charged particles in Jupiter's magnetic field bombard Europa's surface, converting Io's sulfur and other elements into energy-rich compounds.
Europa is constantly flexed by the tidal push and pull of Jupiter and several of its other moons, generating heat that keeps the water under the ice liquid.
Beneath Europa's ocean lies a seafloor and mantle of rock. In direct contact with the ocean, the rocky seafloor could provide the nutrients needed for life.
Though Europa is only the size of our own moon, it holds more water than all of Earth's oceans.
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. Plumes and deep fissures may provide other routes into the liquid world beneath.
JOHN TOMANIO, MATTHEW TWOMBLEY, XAQUÍN G.V., VITOMIR ZARKOVIC, NGM STAFF. DEVELOPMENT: SWORDSWEEPER INDUSTRIES. EUROPA OPENING IMAGE: GALILEO PROJECT/NASA/JPL; REPROCESSED BY TED STRYK; EUROPA WEDGE ANIMATION AND SURFACE ART BY DANA BERRY. SOURCE: KEVIN HAND, JPL/CALTECH