To find out, Lathrop spent the summer testing his new orb and its rotating mechanism. This fall, he will fill it with molten sodium, set it spinning at 90 miles an hour, and see what happens. Although scientists in Europe have produced electromagnetic fields by pushing liquids through pipes or mixing them in cylinders, none of these setups resembled a planet. "We have some inkling about how the Earth generates its electromagnetic field," Lathrop says. "But we can't predict what the field will do next."