Science: Mercury's Magnetism

The tiny craft had been in space for 16 months and was nearly out of steering fuel. Yet flight controllers at Pasadena's Jet Propulsion Laboratory last week managed to keep Mariner 10 alive and performing well through its third —and closest—encounter with the solar system's innermost planet. As it passed only 200 miles above Mercury's scorched surface, the half-ton robot swooped over the planet's north polar region, sent back some 300 closeup pictures and confirmed a puzzling fact-that Mercury has an innate magnetic field

Close Look. The four-hour flyby was an unexpected bonus at the end of an already successful $100 million...

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