This illustration shows how oxygen is generated at Europa as a result of interaction between the Jovian moon's icy surface and Jupiter's plasma environment.

A segment of Europa is cut away in the graphic to show its three layers – the icy shell, the ocean thought to be beneath the shell, and the moon's rocky mantle. Vertical "plasma flow streamlines" depict the flow of these charged particles in the vicinity of the moon. Some of the streamlines are oriented in such a way that their charged particles impact the moon's surface and split frozen water molecules present there into individual oxygen and hydrogen molecules.

The newly created hydrogen molecules rise and form Europa's tenuous atmosphere. Because the newly created oxygen molecules are heavier than hydrogen, they remain closer to the surface. Scientists believe these "bound" oxygen gases could migrate inward toward the moon's subsurface ocean, as depicted in the inset image in the upper right of the illustration.

The white specks surrounding Europa represent "pickup ions" – ionized particles that have been shed from Europa's atmosphere. When molecules in the atmosphere become charged, they are "picked up," or swept, into the stream of charged material flowing around Europa.

Measurements of the composition and quantity of these pickup ions by NASA's Juno mission provided the data necessary to determine the oxygen and hydrogen generation processes at the surface of Europa.