Wednesday, July 21, 2021

EUROPE - JUPITER'S MOON

It is among the four largest moons of Jupiter, with a diameter of 3121.6 km, being slightly smaller than Earth's Moon.  Originally named Jupiter II by Galileo (because it was Jupiter's second satellite in distance; the other four discovered satellites would be numbered corresponding to their distance from the planet), Europa was in Greek mythology the daughter of Agenor.  Abducted by Zeus, who had taken the form of a white bull, she was so enchanted by the docile animal that she decorated it with flowers and mounted it.  Zeus seizes the opportunity and takes her to the island of Crete, where she reveals herself in her true form.  From then on, Europa would have many children with Zeus.

 Europe was discovered on January 8, 1610 by astronomer Galileo Galilei.  It was the first time a moon was discovered orbiting a planet beyond Earth.  The discovery was also important to confirm the understanding that planets revolve around the Sun and not around the Earth.

 The core of this icy satellite is metallic, composed largely of iron and nickel.  This one is surrounded by a rocky shield which is in turn surrounded by a shell of liquid water below another frozen solid.  Galileo's images of Europa suggest that an ocean of liquid water may lie beneath a surface layer of ice nearly ten kilometers thick.

 Every 3.5 days Europa completes an orbit around Jupiter, and like Earth's Moon, it always displays the same face to the gas giant.  However, its eccentric elliptical orbit determines the heights of its tides, which are higher when close to Jupiter.  Thus, tidal forces rise and fall on the sea beneath its ice crust, causing constant movement that is likely to cause the cracks seen in Europa's surface images.

 This constant movement of Europa's tides even causes the moon's temperature to rise beyond normal.  Despite its distance from the Sun being five times greater than Earth's, in addition to the ice crust, the heat of Europa's ocean would be enough to sustain life.

 Intersecting dark fields seen in Europa's images represent the extensive effects of fractures and possible eruption of gases and rocky material from the moon's interior.  It is believed that many of the dark spots between the cracks also resulted from meteor impacts.  Dozens of shallow craters seen in some terrains are likely impact craters.  An impact crater was recently discovered and photographed by NASA's Galileo spacecraft camera.

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