NASA scientists have found evidence that Mars once had plate tectonics reshaping its surface. Data from Mars Global Surveyor has been stitched together to create a planetary map of magnetism. This map shows striping, where two plates were once pushed apart by new molten lava coming up from under the surface. This new lava become magnetized in the direction of Mars magnetic field at the time. Since this magnetic field flipped several times through the planet's history, the stripes provide a record of when Mars' plates were active.