Changes

By far the most salient problem that Europa poses for uniformitarians is its apparent "geologic youth." How such "young" bodies as Europa and its inner neighbor [[Io]] came to participate in a three-part orbital resonance with a so-much-"older" body ([[Ganymede]]) begs explanation. Those wishing to assert that Io and Europa did indeed form much more recently than did Ganymede (and [[Callisto]], the fourth member of the family of Galilean moons) must be prepared to state where those two bodies came from, if they did not form at the same time as the rest of the [[solar system]].

By far the most salient problem that Europa poses for uniformitarians is its apparent "geologic youth." How such "young" bodies as Europa and its inner neighbor [[Io]] came to participate in a three-part orbital resonance with a so-much-"older" body ([[Ganymede]]) begs explanation. Those wishing to assert that Io and Europa did indeed form much more recently than did Ganymede (and [[Callisto]], the fourth member of the family of Galilean moons) must be prepared to state where those two bodies came from, if they did not form at the same time as the rest of the [[solar system]].

At least some authorities assert that Io, for example, only ''looks'' "young" because its volcanoes are constantly filling in any impact craters that are forming. Others assert that Europa looks "young" because its subterranean liquid ocean, if it has one, is resilient and thus able to absorb most meteor impacts without forming craters.<ref name=whyfiles>"[http://whyfiles.org/060moons/europa.html Europa--orbiting incubator]?" ''The Why Files''. Accessed March 1, 2008.</ref> Yet the persistence of the three large impact craters known to exist on Europa contradicts this explanation. So does the decision of the Galileo mission planners to crash-dive the Galileo craft onto Jupiter to prevent a crustal rupture. If the crust were that delicate, then any one of the three objects that formed those craters ought to have ruptured the crust.

At least some authorities assert that Io, for example, only ''looks'' "young" because its volcanoes are constantly filling in any impact craters that are forming. Others assert that Europa looks "young" because its subterranean liquid ocean, if it has one, is resilient and thus able to absorb most meteor impacts without forming craters.<ref name=whyfiles>"[http://whyfiles.org/060moons/europa.html Europa--orbiting incubator]?" ''The Why Files''. Accessed March 1, 2008.</ref> Yet the persistence of the three large impact craters known to exist on Europa contradicts this explanation.

== Exploration ==

== Exploration ==