The hottest action hero of 2004 is 4 feet tall, looks like a golf cart and stars in a feel-good Mars mania blockbuster that is gripping the nation. The arrival of NASA’s Spirit rover on the surface of Mars Saturday night has thrown into sharp relief public and scientific fascination with this planetary neighbor. The rover’s every move has been leading nightly newscasts. From 3:01 a.m. ET Saturday to 9 a.m. ET Thursday, the NASA Web site received 1.45 billion hits. NASA officials believe this will be the biggest online event ever for the U.S. government.