Spirit and Opportunity, NASA’s Mars Exploration Rovers, are global hits: specifically, they’re 6.53 billion hits, more than the Earth’s worldwide population. Since Spirit’s landing on Jan. 4, NASA’s Web Portal has served up images, web cast NASA Television mission coverage and provided Internet users a direct link to the agency’s ongoing exploration of Mars. Early this week, the hit count passed the world population, which the U.S. census estimated Thursday morning at more than 6.3 billion people.