Scientists still don’t know exactly how the Earth generates the magnetic field that keeps a compass needle pointing north. But geophysicist Dan Lathrop is trying to find out. At the University of Maryland, his ‘baby Earth’ towers over him, a massive stainless steel sphere that looks like a prop from some old science fiction movie. Later this year he plans to fill it with molten metal and set the whole 26-ton ball spinning. At top speed the equator will whirl by at 80 miles an hour.