The moons of Jupiter known today as Callisto, Europa, Ganymede and Io were discovered by Galileo Galilei on January 8, 1610. In his honour they are referred to as the Galilean Moons.
In the history of Astronomy, Galileo’s discovery is important because it supported Copernican theory which held that at the centre of the Solar System was the Sun, not the Earth (as was believed in Galileo's day), and that all of the planets revolved around it.
The current names of the Galilean Moons were suggested by German astronomer Simon Marius (1573-1624), but not formally adopted until the 19th Century.
In Greek mythology, Europa was a Phoenician princess who was seduced and abducted to the island of Crete by Zeus in the form of a beautiful white bull. Their children included King Minos of Crete, keeper of the Minotaur.
Europa is the sixth largest moon in the Solar System. Like our Moon, it is tidally locked with its primary and always presents the same face to Jupiter.
Europa - Image credit: NASA
Astronomers believe Europa has a metal core, surrounded by a rocky mantel, covered by a saltwater ocean, under a layer of ice some 62 miles deep. Jupiter’s gravitational pull on Europa causes tidal forces which generate sufficient heat to produce the moon’s sub-surface ocean, and tectonic forces which crack its icy crust. Liquid material rising through cracks in the moon’s crust has discoloured the ice.
Since it has a sub-surface ocean, astrobiologists consider Europa to be one of the places in the Solar System where life could perhaps exist.
Diameter: 3,122 km, or 1,900 miles
Age: estimated to be 4.5 billion years old
Distance from the Sun: approx. 780 million km, or 485 million miles
Distance from Jupiter: 670,900 km or 414,000 miles)
Orbital period: 3.5 days
Rotational period: 3.5 days
Temperature: never above -160°C (-260°F) at equator; never above -220°C (-370°F) in polar regions
Albedo (light reflectivity): 0.64 – one of the brightest moons in the Solar System, due to its ice-covered surface
Atmosphere: Europa has a tenuous oxygen atmosphere