WASHINGTON, Sept. 14 (Xinhua) -- NASA's Mars rover Opportunity has begun driving back into the Victoria crater at the start of a multi-week investigation on the big bowl's inner slope, according to NASA's mission updates on Friday.

The rover finished the last step of a test in-and-out maneuver checking wheel slippage at the rim of Victoria Crater on Thursday, and then it went ahead into the giant crater. It ended the day by driving about six meters inside the rim.

The mission's first destination inside the crater is a light-toned layer of exposed rock that may preserve evidence of interaction between the Martian atmosphere and the surface millions of years ago.

Victoria exposes a taller stack of ancient rock layers than any crater Opportunity has previously visited during the rover's nearly 44 months on Mars. The mission was originally planned for three months.

"We want to maintain a safe egress route out of the crater for Opportunity, and by completing the back-up drive over the sand ripple at the rim, we have confirmed that we have one," said John Callas, Mars rover project manager at NASA's Jet Propulsion Laboratory. "Opportunity is now exploring the interior of Victoria Crater."