![]() Preliminary analyses of these data are currently being prepared for formal publication. ![]() Margaret Kivelson of the University of California at Los Angeles, who heads Galileo's magnetic fields investigation team. "It's an astonishing result and completely unexpected," said Dr. "Instead of increasing continuously as the spacecraft neared Jupiter, the magnetic field strength took a sudden drop of about 30 percent," said Johnson. Galileo scientists are also trying to determine the cause of the hole they found in Jupiter's magnetic field when the spacecraft was closest to Io. The core was probably formed from heating in the interior of the moon, either when it originally formed or as a result of the perpetual tidal heating driving its volcanoes. John Anderson, team leader of Galileo's celestial mechanics experiment and principal author of the paper published in Science today. At the center is a metallic core, probably made of iron and iron sulfide, about 900 kilometers (560 miles) in radius, which is overlain by a mantle of partially molten rock and crust, according to JPL's Dr. Precise measurements of the spacecraft's radio signal revealed small deviations in Galileo's trajectory caused by the effects of Io's own gravity field.įrom these data, Galileo scientists have determined that Io has a two-layer structure. 7, as Galileo passed by Io on its way to enter orbit around Jupiter. The large, dense core Galileo found within Io was deduced from data taken during the spacecraft's flyby within 899 kilometers (559 miles) of the moon last Dec. Friction created by this action heats and melts rock within Io to produce the volcanoes and lava flows seen all over its surface and huge geysers that spew sulfur dioxide onto Io's landscape. As Io orbits Jupiter, these so-called "body tides" rise and fall due to subtle changes in Io's orbit which, in turn, are caused by the gravitational nudges from Europa and Ganymede, other moons of Jupiter.Īs a result, Io is squeezed like a rubber ball. "Jupiter's massive gravity field distorts the shape of Io in the same way that tides are raised in Earth's oceans by the gravitational tugs of the Sun and Moon," said Johnson. Io is the most geologically active body in the Solar System, and though it is less than a third of Earth's size, it generates twice as much heat as the Earth. Torrence Johnson of NASA's Jet Propulsion Laboratory. These newly identified characteristics of Io may be related to the intense heating of the moon caused by the constant squeezing and distortion of Io in Jupiter's powerful gravitational grip, according to Galileo Project Scientist Dr. If so, it would be the first planetary moon known to have one. The spacecraft also has detected a large "hole" in Jupiter's magnetic field near Io, leading to speculation about whether Io possesses its own magnetic field. Jupiter's volcano-pocked moon Io has been found by NASA's Galileo spacecraft to have a giant iron core that takes up half its diameter, scientists report in today's issue of Science magazine.
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