SATELLITES OF JUPITER Distance From Jupiter Name 10³ Jupiter Period Year of kilometers Radii (days) Discovery Adrastea J14 134 1.76 0.30 1979 Amalthea J5 181 2.55 0.49 1892 1979J2 J15 222 3.11 0.67 1980 Io J1 422 5.95 1.77 1610 Europa J2 671 9.47 3.55 1610 Ganymede J3 1070 15.10 7.15 1610 Callisto J4 1880 26.60 16.70 1610 Leda J13 11 110 156 240 1974 Himalia J6 11 470 161 251 1904 Lysithea J10 11 710 164 260 1938 Elara J7 11 740 165 260 1904 Ananke J12 20 700 291 617 1951 Carme J11 22 350 314 692 1938 Pasiphae J8 23 300 327 735 1908 Sinope J9 23 700 333 758 1914 [Illustration: The state of the interiors of the Galilean satellites can be judged from their sizes and densities. These cross-sectional views represent the best guess following the Voyager flybys as to the composition and structure of the objects. Io, with a density equal to that of the Moon and a long history of volcanic activity, is a dry, rocky object. Europa is less dense, and it probably has a global ocean of ice as much as 100 kilometers thick over a rocky interior. Ganymede and Callisto both have densities near 2 grams per cubic centimeter, suggesting a composition about half water and half rock. There is probably a rocky core surrounded by an icy mantle.] Io Active volcanoes Sulfur and frozen SO₂ Molten silicate interior Europa Global fracture patterns Ice crust Rocky interior Ganymede Fresh craters expose ice Young grooved terrain with intricate fracture Old, dark cratered areas Ice crust Water or ice mantle Callisto Large basins reduced by ice flow Fresh craters expose ice Ice/rock crust Water or ice mantle Moon Mercury