|The Moon Europa as seen by the Galileo probe, via NASA.|
Despite most sources giving credit to Galileo for its discovery, Europa and the other three Galilean Moons were also likely discovered at the same time by Simon Marius. Originally Galileo named the moons the Medician Stars, partly out of his initial uncertainty of their nature and as a way of faltering his future patrons. Marius, however, named the moons according to the suggestion of fellow astronomer Johannes Kepler, invoking the names of the mistresses of Zeus (who was later renamed Jupiter according to Roman mythology), a tradition that has been used in the naming of all of Jupiter's moons since.
Europa was named after a Cretan moon goddess who was absorbed into Greek mythology as a Phoenician Princess who was abducted and raped by Zeus as he took the form as Bull. Sought out by Zeus for her beauty, the Jovian moon of Europa follows in the steps of its namesake.
The first human probe to observe Europa was Pioneer 10 in 1973 and was followed the next year by Pioneer 11. The first images of this sixth moon of Jupiter were grainy and lacked any distinguishing detail. It wasn't until 1979 when the first Voyager probe passed by that images detailed enough to discern surface features were available. It was with these first images that scientific curiosity and debate surrounding Europa bloomed.
While studying images obtained from both Voyager 1 and 2, certain anomalous features were noticed. The most striking were striations that seemed to cover the moon. Named Lineae, these features reached widths of 20 kms (12 mi) across and hundreds to thousands of kilometers in length.
|Europa with its prominent Lineae, via NASA.|
These and other unexpected features seen by future missions such as the the Galileo mission to the Jovian system and the New Horizon probe as it passed by Europa on its way to visit Pluto suggested that the source of the strange features was ice, water ice. But these surface structures suggests something more then just a cold frozen moon. The renewing of the surface and the formation of the long Lineae lent credence to the hypothesis that there was liquid water hidden beneath the icy surface. Not just a little water, but a vast, possibly global ocean.
But with an average surface temperature of 110 K (−160 °C; −260 °F) at the equator, how could there be a subsurface ocean of liquid water? The answer seems to come from the same process that causes the tides here on Earth. As Europa and the other Jovian moons orbit Jupiter, they are pulled on gravitationally at different rates at different times. Similar to the processes that cause the nigh constant volcanism on the innermost of the Galilean Moons of Io, Jupiter's gravity causes tidal forces that heat up the plant. This could, potentially, cause volcanism akin to the deep ocean hydrothermal vents on Earth.
|The 'Ice Rafts' of the Conamara Chaos, via Wikipedia Commons.|
The amount of water that can be found on Europa is staggering. If one takes the average depth of 100 km, there is a volume of 3 × 1018 miles cubed of liquid water. This is over two times the amount of water that can be found here on Earth.
|Europa next to Earth, along with the comparable spheres of water contained by each, via NASA.|
JUICE is the somewhat tortured acronym for the planned European Space Agency (ESA) probe known as the JUpiter ICy moon Explorer. Planned for a 2022 launch, JUICE would reach the Jovian system in 2030 where it will serve out at least a three year mission to visit Europa and two other of the Galilean moons, Callisto and Ganymede. Like Europa, Callisto and Ganymede also appear to have liquid water as well as the observed water ice. While all have the potential for harboring conditions that could be conducive to life, Europa is seen as the most likely to contain such an environment due to its larger amounts of water, hotter internal environments and a far more dynamic surface.
|Artist rendition of the JUICE probe, via ESA.|
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