Europa is an icy moon that orbits Jupiter and it is the sixth largest moon in the solar system. As bodies in the solar system go, it has always been on the B-celebrity list taking its place on the billing behind the planets and other major moons. All that changed in 1995 when the Galilean probe visited the Jovian neighbourhood. Photographs taken by the probe revealed some unusual features in the ice. Giant cracks criss-cross the Europan surface. These fissures seem to indicate the presence of vast oceans beneath the moon's surface. If this is the case then Europa becomes one of the most likely places to find extra terrestrial life. The National Research Council in America has advised NASA that Europa should be given priority equal to Mars in planning for future exploration. Its fair to say that Europa is now on the A-celebrity list. Eat your hearts out Ganymede and Callisto.
It is somewhat surprising to find liquid oceans so far away from the heat of the sun and hidden below thick layers of ice, but similar things happen on earth. Lake Vostok is found under hundreds of metres of ice in antarctica. Intense pressure from the overlying ice combined with geothermal heat from below keeps the water liquid. The geothermal heat inside Europa comes from tidal pumping. As well as Jupiter's massive gravitational pull other sizable moons all have a tug at Europa when they pass and this tidal pressure causes the heart of the planet to heat up. It would not be surprising to find thermal vents at the bottom of the Europan oceans spewing heat and mineral rich materials into the water. A great place for life to take a grip.
In 2008 NASA is planning to send a spacecraft out to orbit Europa looking for potential landing sites where the ice is at its thinnest. This will lay the groundwork for future probes to land and maybe send hydrobots burrowing down to explore the oceans of Europa.