After a slow, deliberate journey of three years, NASA's Mars Exploration Rover Opportunity has reached the red planet's Endeavour crater, the space agency said. The rover completed a 13-mile trip from its previous location, a crater dubbed Victoria, on Wednesday, a NASA release said. Endeavour crater, 14 miles in diameter, features rocks and terrain much older than those examined by Opportunity during its first seven years on Mars, scientists say. That could include clay minerals that may have formed in an early warmer and wetter period on the planet, they say. "We're soon going to get the opportunity to sample a rock type the rovers haven't seen yet," Matthew Golombek at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said. "Clay minerals form in wet conditions so we may learn about a potentially habitable environment that appears to have been very different from those responsible for the rocks comprising the plains." NASA launched Opportunity and its sister rover Spirit in the summer of 2003, and after completing their three-month prime missions in April 2004 they continued years of extended operations.