The twin rovers that will launch from Cape Canaveral next summer and ramble across Mars in early 2004 are yet to be named. Right now, they’re known by the droll monikers “Mars Exploration Rovers” — or MER-A and MER-B. There’s still time to fix that, and NASA is collaborating with the Planetary Society and LEGO Co. to get schoolchildren involved in a contest to name the two robotic explorers.