The Mars rover Opportunity is nearing the end of a three year voyage to the Endeavor crater, a massive formation that has been Opportunity's destination since it left the smaller Victoria crater in August 2008.

The two craters are only about seven miles apart, but Opportunity had to take a more circuitous route to avoid hazards. It also paused periodically to check for obstacles and drove backwards part of the way in an effort to reduce wear and tear on its wheels.

"Opportunity has an arthritic shoulder joint on her robotic arm and is a little lame in the right front wheel, but she is otherwise doing remarkably well after seven years on Mars, more like 70 in 'rover years,'" Bill Nelson, chief of the mission's engineering team, said last month. "The elevated right front wheel current is a concern, but a combination of heating and backwards driving has kept it in check over the past 2,000-plus sols (Martian days)."

Opportunity will be carrying on the work of its fallen comrade Spirit, a now-defunct sister rover that became mired in a sand trap and stopped responding. The edge of the Endeavour crater is named Spirit's Point in homage to the deceased rover.

Along the way Opportunity was able to examine fragments of meteorites and probed the Martian soil for evidence of ancient water deposits. But NASA scientists are already giddy about the possibilities in Endeavor, noting that Opportunity has not yet observed rock formations as old as the craggy outcroppings ringing the crater.

"We will likely spend years at this location," rover project manager John Callas, of NASA's Jet Propulsion Laboratory, told The Associated Press. "What a destination. It's not just one spot. There's kilometers of interesting geology to explore."

Endeavour is about 14 miles wide and lies near the Martian equator.