Enigmatic Face of an Ice Moon: Europa

Europa: Ice Moon of Jupiter

Jupiter and the Galilean Satellites

Top to bottom: Io, Europa, Ganymede, Callisto
Credit: NASA/JPL/DLR (Public Domain)

Discovery of Europa and the Galilean Moons

Europa, an ice moon of the giant planet Jupiter, looms large in the Solar System. Only five other moons in our Solar System outsize Europa; three of them join her in orbit around Jupiter. Italian astronomer Galileo Galilei first witnessed Europa over 400 hundred years ago on January 8, 1610. Unleashing one of the great controversies of the period, Galileo famously discovered a Jovian system of orbiting moons, including Europa. Coincidentally, this occurred within a very short time of Europa's discovery by another famous astronomer, Simon Marius. Subsequently, each astronomer held firm in a debate over who first cast their sight upon the moon. Ultimately, Galileo first published his discovery. Galileo named these moons "Cosimo's stars", as an homage to Cosimo II de' Medici, Grand Duke of Tuscany.

Marius was a German astronomer with highly respected skills of astronomical observation. He we went on to describe the orbits of these moons with more precision that Galileo. Marius discussed his discovery of the Jupiter moons with another famous astronomer of the time, Johannes Kepler. They decided to name these four moons after mythological lovers of Zeus (the Greek equivalent of Jupiter). The world astronomy community accepted these names, despite protests from Galileo and the names have held ever since. In order from smallest to largest, the Galilean satellites are: Europa, Io, Callisto, and Ganymede.

Europa, still an enigma.
Pioneer 10 in 1973
Credit: NASA (Public Domain), via Wikimedia Commons

Detailed Views of Europa Emerge

The familiar variegated geography of our Earth's one moon presents broad open flat-lands, along with harsh ridges, steep valleys, and dramatic craters. We know intimate details of these features thanks to intrepid missions of the Apollo era: from the placid station at the Sea of Tranquility, to the debris laden field of Fra Mauro, and the tumultuous complex features of Hadley–Apennine. Europa, meanwhile, reveals a visage smoother than any other solid object in the Solar System. Centuries of Earthbound telescopic observation had not prepared astronomers for the striking image of Europa. Modern space probe flybys revealed a smooth faced, ice-encrusted moon.

Europa: Galileo spacecraft 1996
Credit: NASA/JPL/DLR (Public Domain), via Wikimedia Commons

The Pioneer 10 spacecraft, launched in 1972, started things off. Pioneer 10 offered up a tantalizing image of Europa, sorely lacking in detail. Astronomers glimpsed a highly reflective surface, with an albedo similar to that of ocean ice. Europa, in fact, shines among the brightest of moons in our Solar System. (The brightest moon, Enceladus, the ice moon of Saturn, reflects nearly one hundred percent of incident sunlight.) 

Pioneer 10 produced a treasure trove of information about Jupiter and its satellites.  However, Europa was not the primary target. Most of what we now know about Europa derives from the accomplishments of an expedition launched in 1989, the Gallileo mission.  Meanwhile, the Hubble Space Telescope detected stunning evidence of water vapor plumes. We have seen other hints of a complex, teeming subsurface world of Europa. More than some far fetched fantasy, there is a reasonable suspicion that Europa might harbor simpler forms of extraterrestrial life. Future missions to Europa are in the works, including the Europa Clipper. This mission, set to launch around 2022, will include multiple flybys, and even more exciting, a landing craft.

Ice Moon Station will publish more on Europa, Pioneer 10, the Gallileo mission, and upcoming missions in future posts.  Subscribe by Email, or follow us on Facebook and  Twitter for updates.