A city-sized impact crater has been found on the frozen surface of Jupiter's moon Europa. Detected by the Galileo spacecraft, the impact zone may shed new light on the enigmatic icy surface of this strange ice-crusted satellite. The scar from the past impact, made by a comet or small asteroid, is revealed in false-colour images. The brightest parts of the image are regions with a high proportion of relatively pure water-ice. Blue indicates non-ice materials are also present.
Astronomers are unsure about the composition of the darker materials.
They may consist of minerals formed by evaporation of salty brines, or they may be rich in sulphuric acid. The ring seen around the impact crater is the ejecta, consisting of icy subsurface material blasted out of the crater by the impact. The darker area in the centre may be debris from the impacting body. Life question Europa is a focus of attention for astronomers because an ocean of liquid water may exist beneath the icy crust, possibly providing an environment suitable for life. The Galileo spacecraft has made many close passes of the moon, and in the future a new spacecraft mission, the Europa Orbiter, will make a more detailed study of this fascinating world.