Looking Back Across Mars

It's been a long trip for the Martian rover Opportunity. Last week Opportunity surpassed Viking 1 as the longest running mission on Mars, now extending well over six years. Pictured above , Opportunity's tire tracks cross a nearly featureless Martian desert, emanating from a distant horizon. Landing in 2004 in Meridiani Planum , the robotic Opportunity has embarked on its longest and most dangerous trek yet, now aiming to reach large Endeavor Crater sometime next year. Endeavor , it is hoped, holds new clues to the ancient geology of Mars and whether Mars could once have harbored life .