Spirit, one of two NASA robots currently exploring Mars has exceeded its life span and is showing signs of wear, but it's still running and still sending back new photos. A new Nature article describes the aging rover's biggest problems: the batteries are running low due to weak winter sunlight and the gearbox on right front wheel has developed a fault. NASA engineers have instructured the rover to drive backwards, which reduces the excessive current being drawn by the front wheel. The weak light on Mars now allows only enough battery power for an hour or two of activity each day. Mars and Earth will be out of communications for a week around September 10 and the current plan is to have Spirit hibernate all week while it's batteries recharge. Despite the problems Spirit has traveled over 3 kilometers from its landing site and is now halfway up the 200 meter-high Columbia Hills.