The blue water of Buzzards Bay glittered as boats bobbed on the gently undulating surface and gulls swooped among their sails. The seaside air at the Woods Hole Oceanographic Institution was thick with the sweet smell of grass and the tang of saltwater. This was late summer on Cape Cod - our ocean world at its most inviting.

But inside a bay-view conference center, 80 scientists were conjuring up very different ocean worlds: The ice-covered moon Europa, whose watery interior is kept liquid by the gravitational pull of Jupiter. Enceladus, whose south pole emits geyser-like sprays of water vapor, gas and ice; as it orbits Saturn, the tiny moon leaves a glowing trail of particles in its wake.

And then there were the dark, seething systems at the bottoms of our own seas, where the Earth's crust cracks open, spewing rock, gas and heat - a world as alien to humans as any in outer space.

These ocean worlds are forbidding, hostile, sunless and remote - but many scientists believe they also hold the key to life. Some 4 billion years ago, one hypothesis goes, the chaotic chemistry at the ocean floor provided the fuel for Earth's first organisms. If life arose elsewhere in our solar system, it probably started under similar circumstances. The only way to know for sure is to go look for it.

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