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[[Image:Europa true color.jpg|150px|left]]: ''Main article: [[Europa]]''

[[Image:Europa true color.jpg|150px|left]]: ''Main article: [[Europa]]''

'''Europa''', the second innermost, is also the smallest of the Galileans. It has very few craters, and thus by [[uniformitarianism|uniformitarian]] criteria it is considered "young." The thick ice sheet that overlays it has fueled speculation, in the scientific community and in [[science fiction]], that it harbors life. The [[Galileo project|Galileo]] spacecraft discovered evidence that Europa has a sub-crust saltwater ocean under a very thin rock-and-ice layer--and in order to prevent the spacecraft from crashing into Europa, rupturing the crust, and contaminating Europa's oceans with earthly [[microbe]]s, Galileo's mission controllers steered Galileo into a crash dive into Jupiter in September of 2003.<ref name=rense/><ref name=Macey/>

'''Europa''', the second innermost, is also the smallest of the Galileans. It has very few craters, and thus by [[uniformitarianism|uniformitarian]] criteria it is considered "young." The brittle ice sheet that overlays it has fueled speculation as to whether a much thicker ice sheet, or a liquid-water ocean, lies deep to it. This in turn has fueled speculation, both in the scientific community and in [[science fiction]], as to whether Europa harbors life.

 

The [[Galileo project|Galileo]] spacecraft developed evidence in favor of the proposition that Europa has a sub-crust saltwater ocean under a very thin rock-and-ice layer. In order to prevent the spacecraft from crashing into Europa, rupturing the crust, and contaminating Europa's oceans with earthly [[microbe]]s, Galileo's mission controllers steered Galileo into a crash dive into Jupiter in September of 2003.<ref name=rense/><ref name=Macey/> However, the exploration of Europa with a submersible probe, to be delivered by an ice-penetrating missile, is under active consideration.

== Ganymede ==

== Ganymede ==