Until then I’d thought I was born a generation too soon to explore other worlds.  But that week, getting hold of a face mask and snorkel and swimming out into multihued gardens of living rock, fan and branching corals, shoaling fish, sea turtles and a small hammerhead shark cruising past me with predatory grace, I realized there was a whole other alien world right off the seawall. Today we send probes to Mars, Pluto and Jupiter’s moon Europa and what’s the first thing we look for as a sign of life? Water. Yet we’re living on a blue water planet that’s little explored yet highly vulnerable to our human behaviors.