Europa is the smallest of the Galilean satellites of Jupiter with a diameter of 3050 kilometers. It has a density of 3.2 grams per cubic centimeter which means it is mostly a rocky body with a composition like the earth's crust: silicate-rick rocks. It's surface composition has been well- determined from spectroscopic studies. It's high reflectivity of 64 percent, along with certain other aspects of its reflected light indicate a surface almost completely covered by a layer of water frost. At its distance from the sun, its surface temperature is about 130 degrees on the Kelvin scale.
From models of its deep interior, astronomers have concluded that its interior is about 10 percent water and 90 percent silicate material. The core silicate region is at a temperature of 2800 K, heated by a combination of radioactive element decay and the gravitational stresses produced by Jupiter being so close. Their is an ice crust about 10 - 50 kilometers thick floating on top of a sea of liquid water which is 200 kilometers or so thick. The water layer has a temperature from 350 K nearest the core, to 270 K just below the ice crust.
Voyager 2 images of Europa confirm that it has an icy crust, with only a dozen craters and numerous thin faults criss crossing its entire surface like the markings from a shattered egg shell. Ice rafts (above right photo) also mimic 'rafting' seen in the arctic regions. Any objects impacting the surface penetrate the ice crust and traces of the impact are obliterated by the crustal dynamics which are driven by Jupiter's tidal influences.
It is exciting to think that three prerequisites for life are present on Europa. It has vast quantities of liquid water; energy inputs; and minerals in solution. Whether organic life could emerge from this slurry is not known.
Copyright 1997 Dr. Sten Odenwald
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