Jupiter’s moon Europa has long been regarded as one of the most likely places in the solar system where some form of life could exist outside of Earth. Evidence from visiting spacecraft has shown that it almost certainly has a liquid water ocean beneath its icy surface. That water is also thought to be similar to that in Earth’s salty oceans and rich in oxygen.
Obtaining any answers to the life question however will require further missions to be sent there, and that is the tricky part. The costs involved have pushed back such missions; the current mission proposal, the Europa Jupiter System Mission, would launch sometime within this decade. Europe would then follow with its own mission to Ganymede, another Jupiter moon thought to have a subsurface ocean.
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