Moonstruck
"We're fairly confident that our theories are on the right track. But we're not all the way there yet." Margaret Kivelson
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Twenty years ago, Professor of Earth and Space Sciences Margaret Kivelson wrote a scientific paper speculating that planets might not be the only celestial bodies to exert magnetic spheres of influence. The paper was skeptically received, and even Kivelson considered the hypothesis mostly an "intellectual exercise." So Imagine Kivelson's surprise two years ago when the Galileo spacecraft flew by Ganymede, Jupiter's largest moon, and sent back experimental data proving she'd been right all along. The experiments, which Kivelson designed, not only provided the first indisputable evidence that a moon can generate an internal magnetic field; it caused scientists to rethink the conditions under which such fields can occur. The internal processes that enable some planets -- and, which the Ganymede evidence, some moons -- to create magnetic fields has long served as one of the greatest puzzels of the natural sciences. The Ganymede findings were so startling because the moon appears as an icy, geologically inactive mass, a state inconsistent with assumed magnetic-field prerequisites. "It's a mystery," Kivelson says, referring to the question of how currents might come out of the snowball-like satellite. "We're fairly confident that our theories are on the right track. But we're not all the way there yet." Indeed, researchers are currently re-examining theories on Ganymede's thermal evolution. Kivelson has also been studying the effects Ganymede's magnetic field has on the surroundings of Jupiter's magnetosphere. Flowing plasma rotating around Jupiter interacts with Ganymede's field to create a magnetosphere around Ganymede. "This is itself an interesting object," Kivelson explains. "It can trap charged particles, and it can protect parts of Ganymede's surface from being bombarded by the energetic charged particles in the environment." Kivelson's UCLA colleague, Krishan Khurana, is pursuing the promising lead that surface properties - i.e., how the ices have been altered by charged-particle bombardment in some regions but not others - can confirm the magnetic geometry of a system. And Ganymede's magnetosphere provides a new model for testing many theories related to Earth's own magnetic field. "A lot of attention is being given to what we call 'space weather' - how the Earth's electromagnetic properties change in time because of its interaction with the solar wind," explains Kivelson. "It is a practical area of study in that all of our satellites are embedded in this magnetosphere." |
In addition to Ganymede, Kivelson has discovered important data on Jupiter's other moons, as well. The Galileo flyby of Io, a moon with volcanoes, surrounded by a corona of neutral gases and charged particles that may have originated from the volcanic sources, showed surprising significant magnetic perturbations, suggesting it also generates its own internal magnetic field. And multiple passes by the moons Europa and Callisto suggested that magnetic changes around these moons are the result of fields that are inductive, rather than internal. "We have concluded that the electrical current-carrying path has to be somewhere quite close to the surface," says Kivelson. The surfaces of both moons are water ice - not a good electrical conductor - but the culprit might be liquid saltwater, similar to the oceans on this planet. "The most plausible interpretation of our results is that somewhere not very far below the surface, the ice has melted, or at least come close enough to melting that it's creating an inductive response roughly comparable to that created by Earth's oceans." Kivelson hopes to be able to draw more definitive conclusions after the next scheduled pass by Europa sometime within the next year. The answers have been a long time coming for Kivelson, who became a physicist back in the early '50s, when a scant 2 percent of physics Ph.D.s were awarded to women. She spent more than a decade working in plasma physics at RAND, the Santa Monica-based think tank, then in 1967 accepted a faculty position with UCLA's Institute of Geophysics and Planetary Physics. Before long, she was managing a team analyzing magnetic-field data from two Pioneer spacecraft missions to Jupiter. In 1976, she first proposed building the magnetometer for Galileo. A team of UCLA researchers and engineers began to implement Kivelson's design the following year, but numerous delays would keep Galileo Earth-bound for 13 years before it finally began its six-year, 2.3 billion-mile journey to Jupiter in 1989. "It was an investment of time that I'm not sure I would have made if I had known it was going to be close to 20 years before I got the first data," Kivelson says, smiling. "But certainly the payoff has been incredible." - Dan Gordon
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