Re: Could Europa's ice ever have been a liquid?

It's not only a plausible theory, there's also
evidence to support it.  Europa's ice crust contains very
long fissures which extend over a good deal of the moon's
surface and superficially resemble the plate divisions of
Earth's continents and ocean bottoms.  This indicates that
Europa's interior was once liquid, or at the very least, slushy!

While the coalescing outer planets and moons were hotter
in the distant past, they were not hot enough to give off
appreciable amounts of ultraviolet radiation, ignoring the
effects of their planetary magnetic fields (which still exist
today).  A body gives off significant ultraviolet radiation
only once its temperature exceeds several thousand degrees.