NASA MAY HAVE equipped its Mars Curiosity rover with an impressive array of scientific instruments, but the robot attaché’s size and $2.5-billion price tag give its operators ample reason to steer clear of terrain that could jeopardize its mission. Which is a shame, because much of Mars’ craggy, cave-ridden, boulder-strewn landscape is so treacherous (planetary geologists literally call it chaos terrain), that big, expensive robots like Curiosity can’t risk accessing it. That’s why NASA’s Jet Propulsion Laboratory built Puffer.