Discovery: Jan 7, 1610 by Galileo Galilei Diameter (km): 3,138 Mass (kg): 4.8e22 kg Mass (Earth = 1) 0.0083021 Surface Gravity (Earth = 1): 0.135 Mean Distance from Jupiter (km): 670,900 Mean Distance From Jupiter (Rj): 9.5 Mean Distance from Sun (AU): 5.203 Orbital period (days): 3.551181 Rotational period (days): 3.551181 Density (gm/cm³) 3.01 Orbit Eccentricity: 0.009 Orbit Inclination (degrees): 0.470 Orbit Speed (km/sec): 13.74 Escape velocity (km/sec): 2.02 Visual Albedo: 0.64 Surface Composition: Water Ice
Europa is the smallest of the four Galilean moons, but it is still the 6th largest satellite in the solar system. With a diameter of 3,138 km, Europa is slightly smaller than our own Moon.
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Europa is the smoothest object in the solar system. The satellite has a mostly flat surface, with nothing exceeding 1 km in height. The surface of Europa is also very bright, about 5 times brighter than our Moon.
There are two types of terrains on Europa's icy crust. One type of terrain is mottled, brown or gray in color and consisting of mainly small hills. The other type of terrain consists of large smooth plains criss-crossed with a large number of cracks, some curved and some straight. Some of these cracks extends for thousands of kilometers. The cracked surface appears remarkably similar to that of the Arctic Ocean on Earth. The crust may be no thicker than 150 km.
There are very few craters observed on Europa, particularly large craters. The lack of craters indicates a young age for the surface, perhaps as young as 30 million years old. The inner core of Europa is suspected to be iron-sulfur, similar to that of Io. Since Europa has a lower density than Io (3.01 gm/cm?3), the size of the inner core is expected to be smaller than Io's. A tenous atmosphere of oxygen has been detected on Europa.
There is a possibility that a liquid ocean exists under the icy crust of Europa. The ocean may be present due to warming from a tidal tug-of-war with Jupiter and the other Galilean satellites. Similar tidal heating drives the volcanoes on Io. Recent Galileo images have provided evidence that Europa had a liquid ocean or "warm ice" underneath the crust, but it is not clear if this ocean exists to the present day.
Water geysers may exist on Europa, though none has yet to be observed. If an ocean exists on Europa, then it may be possible that life exists in these oceans, though the odds for that are small. However intriguing this idea is, there is no evidence of life on Europa - it is purely conjecture at this point.
Of the four Galilean moons, Europa was the most poorly observed by Voyager. Galileo had three close flybys of Europa during its primary mission. Galileo is now in a extended mission called the Galileo Europa Mission, which focuses on an intensive study of Europa.
