The passage informs us that water is ....... .

Ever since 1979, when pictures sent back from the
two "Voyager" probes revealed that one of Jupiter's
moons, Europa, was wrapped in cracked ice,
scientists have suspected the existence of an ocean
of water beneath its surface. This has excited those
interested in searching for extra-terrestrial life.
Water is widely regarded as necessary, if not
sufficient alone, to sustain living things. Further flybys
of Europa by "Galileo", a spacecraft that has
been in orbit around Jupiter since 1995, have
provided additional evidence through more detailed
pictures.