A major dust storm has developed on the red planet, blocking sunlight and prompting Mars mission managers to keep a close eye on it, SPACE.com has learned. It is not known how large the storm might grow, but already it is thousands of miles across. If it balloons, as dust storms have done in the past, it could hamper operations of NASA's Mars rovers Spirit and Opportunity. For now, officials don't think the storm will threaten rover operations, however. In fact, the windy conditions on the planet have blown off large amounts of dust from the rovers' solar arrays, giving...