The moons of Jupiter have oceans. Beth Tyler 06.01.01 Jupiter has four orbiting moons. The first two moons, Io and Europa, have salty oceans like the Earth. Last year, scientists discovered that the third moon of Jupiter, Ganymede, also has an ocean, although its ocean is far beneath the icy surface. Astronomers have a spacecraft that flies around Jupiter taking pictures and measurements. This spacecraft, called Galileo, has been in orbit around Jupiter since 1995. The scientists cannot actually see the oceans, but measurements from Galileo’s magnetometer, an instrument that measures magnetic fields, indicate that water is present below the surface.     Planets and stars create magnetic fields by sending out electric currents into space. This field around the planet or star can be detected and measured. The bigger a planet or star is, the stronger its magnetic field is. Because Jupiter is very large and its moons are nearby, Jupiter’s magnetic field runs through the moons. When the magnetic field hits water below the surface of a moon, it produces more magnetic fields that stretch out from the deep oceans. These are the magnetic fields Galileo measured coming from Ganymede. While these magnetic fields are not proof of an ocean below the surface on Ganymede, they offer very strong evidence for the presence of water. CLICK HERE for more information! Kerr, Richard A. 2001. Jupiter's two-faced moon, Ganymede, falling into line. Science 291(5501): 22-23. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.