Jupiter and Saturn are the two largest planets in the solar system and the first two gas giant planets encountered when moving away from the Sun. They are both immensely complicated systems not unlike miniature solar systems on their own: Jupiter has 63 known moons and its own ring system, whereas Saturn is famous for its rings and 62 known moons. Astronomers are finding with some regularity new, distant moons orbiting each of these planets, so their number of known satellites continues to grow.
Linda T. Elkins-Tanton, Ph.D., has a doctorate in geology and geophysics from the Massachusetts Institute of Technology (MIT). She is an expert on volcanic processes in terrestrial planets, effects of meteorite impacts, early lunar evolution, and the connections between meteorite impacts, flood basalts, and global extinction events. She has been published in the journals Geology, Earth, and Planetary Science Letters; Geophysical Research Letters; and Geochimica et Cosmochimica.