This is Part Four of a six-part series telling the story of humankind's efforts to understand the origins of life and the potential for life on other worlds by studying organisms that survive deep below Earth's oceans around hydrothermal vents.
When the Voyager and Galileo spacecraft visited Jupiter's moons Io and Europa, scientists were faced with the exciting possibility that these strange worlds might host exotic forms of life. Scientists observed that Europa was rich with water in its icy outer layer. If there was tidal heating on Europa, could it be enough to melt the bottom of the moon's ice crust, perhaps enough to sustain a liquid water ocean?
Europa does experience strong tidal forces. The moon orbits close to Jupiter, and the giant planet's gravity stretches the 2,000-mile wide Europa by more than 100 feet. This makes the moon's orbit ever-so-slightly non-circular, giving the orbit a tiny eccentricity, but one with enormous implications. Huge tidal forces are the crucial factors that suggest Europa's ocean is able to remain in its liquid water phase instead of freezing completely into the layer of ice above it. According to planetary scientists, everything interesting about Europa follows from this subtle eccentricity.
If a liquid ocean exists on Europa, could the seafloor be similar to our own oceans here on Earth? In the absence of sunlight, could hydrothermal vents provide the necessary energy to support ecosystems on the icy moon?
Last Updated: 26 February 2013