In 1999, NASA's Mars Global Surveyor first brought back a tantalizing hint that Mars once might have had an earth-like system of plate tectonics. But the observations covered only a small region and were too spotty to confirm. Now astrophysicists have stitched together comprehensive planetary map of Mars's surface. The map shows striping – a phenomenon created when hot lava pushes two tectonic plates apart as it forces its way to the surface. Since the new lava becomes magnetized in the same direction of the planet's magnetic field, and since the planet's magnetic field periodically flips directions, the striping also provides a record of plate activity through the planet's history. More from nasa.gov.