... They had expected to see impact craters like those on the other terrestrial bodies and from their number per unit area to estimate the age of Io's surface. ... This may have been the most important single discovery of the Voyager missions; it was the first real proof that the interiors of other "terrestrial" bodies are actually hot and active. ... A nalysis of the Voyager images led scienties to believe that the lava flows on Io's surface were composed mostly of various compounds of molten sulfur. ...
Jupiter is the largest of the nine planets, more than 10 times the diameter of Earth and more than 300 times its mass. ... The mean density of Earth is 5.245 times that of water. The pull of gravity on Jupiter at the top of the clouds at the equator is 2.4 times as great as gravity's pull at the surface of Earth at the equator. ... It is tipped about 11њ to Jupiter's axis of rotation, similar to Earth's, but it is also offset from the center of Jupiter by about 10,000 kilometers (6,200 miles). ...