At http://phys.org/print362821573.html … Europa is a moon of Jupiter and the link provides some historical information on the discovery, by telescope (the kind you hold in your hand), of the object some few hundred years ago.
Lots of speculation amongst the information. Lots of good thinking too. Plus news of an upcoming NASA mission to Europa. It has water, and oxygen, and appears to be one of the most favourable planets or moons worth paying a drop in visit by humans.