This artist's impression shows Jupiter and its moon Europa using actual Jupiter and Europa images in visible light. The Hubble ultraviolet images showing the faint emission from the water vapor plumes have been superimposed, respecting the size but not the brightness of the plumes. Astronomers using Hubble have detected signs of water vapor being vented off this moon, creating variable plumes near its south pole: the first observational evidence of water vapor being ejected off the moon's surface.