Europa Moon

Europa i is the sixth closest moon of the planet Jupiter, and the smallest of its four Galilean satellites, but still one of the largest moons in the Solar System. Europa was discovered in 1610 by Galileo Galilei[1]and possibly independently by Simon Marius around the same time. Progressively more in-depth observation of Europa has occurred over the centuries by Earth-bound telescopes, and by space probe flybys starting in the 1970s. Slightly smaller than Earth’s Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily ofoxygen. Its surface is composed of water ice and is one of the smoothest in the Solar System. This surface is striated by cracks and streaks, while cratering is relatively infrequent.

The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life.[12] This hypothesis proposes that heat energy from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics.[13] The Galileo mission, launched in 1989, provided the bulk of current data on Europa. Although only fly-by missions have visited the moon, the intriguing characteristics of Europa have led to several ambitious exploration proposals. The next mission to Europa is the European Space Agency’s Jupiter Icy Moon Explorer (JUICE), due to launch in 2022.[14] Discovery and naming

Europa was discovered on January 8, 1610 by Galileo Galilei,[1] and possibly independently by Simon Marius. The moon is named after a Phoeniciannoblewoman in Greek mythology, Europa, who was courted by Zeus and became the queen of Crete. Europa, along with Jupiter’s three other largest moons, Io, Ganymede, and Callisto, was discovered by Galileo Galilei in January 1610. The first reported observation of Io was made by Galileo Galilei on January 7, 1610 using a 20x-power, refracting telescope at the University of Padua. However, in that observation, Galileo could not separate Io and Europa due to the low power of his telescope, so the two were recorded as a single point of light. Io and Europa were seen for the first time as separate bodies during Galileo’s observations of the Jupiter system the following day, January 8, 1610 (used as the discovery date for Europa by the IAU).[1] Like all the Galilean satellites, Europa is named after a lover of Zeus, the Greek counterpart of Jupiter, in this case Europa, daughter of the king of Tyre. The naming scheme was suggested by Simon Marius, who apparently discovered the four satellites independently, though Galileo alleged that Marius had plagiarized him.

Marius attributed the proposal to Johannes Kepler.[15][16] The names fell out of favor for a considerable time and were not revived in general use until the mid-20th century.[17] In much of the earlier astronomical literature, Europa is simply referred to by its Roman numeral designation as Jupiter II (a system introduced by Galileo) or as the “second satellite of Jupiter”. In 1892, the discovery of Amalthea, whose orbit lay closer to Jupiter than those of the Galilean moons, pushed Europa to the third position. The Voyager probes discovered three more inner satellites in 1979, so Europa is now considered Jupiter’s sixth satellite, though it is still sometimes referred to as Jupiter II.[17] Europa orbits Jupiter in just over three and a half days, with an orbital radius of about 670,900 km. With an eccentricity of only 0.009, the orbit itself is nearly circular, and the orbital inclinationrelative to the Jovian equatorial plane is small, at 0.470°.[18] Like its fellow Galilean satellites, Europa is tidally locked to Jupiter, with one hemisphere of the satellite constantly facing the planet. Because of this, there is a sub-Jovian point on Europa’s surface, from which Jupiter would appear to hang directly overhead.

Europa’sprime meridian is the line intersecting this point.[19] Research suggests the tidal locking may not be full, as a non-synchronous rotation has been proposed: Europa spins faster than it orbits, or at least did so in the past. This suggests an asymmetry in internal mass distribution and that a layer of subsurface liquid separates the icy crust from the rocky interior.[20] The slight eccentricity of Europa’s orbit, maintained by the gravitational disturbances from the other Galileans, causes Europa’s sub-Jovian point to oscillate about a mean position. As Europa comes slightly nearer to Jupiter, the planet’s gravitational attraction increases, causing the moon to elongate towards it. As Europa moves slightly away from Jupiter, the planet’s gravitational force decreases, causing the moon to relax back into a more spherical shape. The orbital eccentricity of Europa is continuously pumped by its mean-motion resonance with Io.[21] Thus, the tidal flexing kneads Europa’s interior and gives the moon a source of heat, possibly allowing its ocean to stay liquid while driving subsurface geological processes.[13][21] The ultimate source of this energy is Jupiter’s rotation, which is tapped by Io through the tides it raises on Jupiter and is transferred to Europa and Ganymede by the orbital resonance.[21][22]