After two years of driving and drilling on Mars, NASA's Curiosity rover has reached its "far frontier": the base of a giant Martian mountain.

The Curiosity rover has reached the base of the 3.4-mile (5.5 kilometers) mountain Aeolis Mons, unofficially dubbed Mount Sharp, NASA officials announced in a news conference today (Sept. 11). After landing on the Red Planet in 2012 and driving close to 5.6 miles (9 km), Curiosity is now preparing to dig into the Martian dirt, probing the mountain's base for clues about the planet's past.

The announcement also comes on the heels of a somewhat critical science review of the Curiosity mission. [See amazing photos from the Curiosity rover]

"I think the principle recommendation of the panel is that we drive less and drill more," Curiosity project scientist John Grotzinger said during the news conference. "The recommendations of the review and what we want to do as a science team are going to align because we have now arrived at Mount Sharp."

This map depicts lower Mount Sharp on Mars, with the major geologic units identified from orbit. Image released Sept. 11, 2014.
This map depicts lower Mount Sharp on Mars, with the major geologic units identified from orbit. Image released Sept. 11, 2014.
Credit: NASA/JPL-Caltech/Univ. of Arizona

Curiosity has just been approved for a two-year extended mission, and now that the rover has gotten to the base of the mountain, it should drill into more rocks to learn more about Mars' past, said Grotzinger.

"It's really an honor and a privilege for me to be able to tell you all that we have finally arrived at the far frontier that we have sought for so long," Grotzinger said.

NASA's Mars Curiosity rover views the "Amargosa Valley," on the slopes leading up to Mount Sharp. Image released Sept. 11, 2014.
NASA's Mars Curiosity rover views the "Amargosa Valley," on the slopes leading up to Mount Sharp. Image released Sept. 11, 2014.
Credit: NASA/JPL-Caltech/MSSS

Mission controllers on Earth brought Curiosity to Mount Sharp via a somewhat different path than initially planned. Partially due to unexpected wear on the 1-ton rover's wheels and new science data, scientists took the rover on a path to the south, which led to the rover's arrival at the base of the Mount Rainier-sized mountain earlier than expected.

Curiosity will now start examining an area called Pahrump Hills instead of rolling on to another point called Murray Buttes and moving into the mountain's terrain there as previously planned, according to NASA officials.

"It has been a long but historic journey to this Martian mountain," Grotzinger said in a statement. "The nature of the terrain at Pahrump Hills and just beyond it is a better place than Murray Buttes to learn about the significance of this contact. The exposures at the contact are better due to greater topographic relief."

The Curiosity rover landed in the Gale Crater on Mars in August 2012 after launching to space in 2011. The $2.5 billion Curiosity mission accomplished its primary objective by discovering that Mars did once have the conditions for habitability.

Scientists controlling the rover eventually want to examine the sedimentary layers of the foothills of Mount Sharp to see if they have preserved evidence of Mars' transition from a warm, wet world to the cold and dry one we see today.

This mesa within the "Murray Buttes" area on Mars evinces a complex fracture pattern (black arrow) protruding from the eroding rock. Image taken with the High Resolution Imaging Science Experiment (HiRISE) camera. Image released Sept. 11, 2014.
This mesa within the "Murray Buttes" area on Mars evinces a complex fracture pattern (black arrow) protruding from the eroding rock. Image taken with the High Resolution Imaging Science Experiment (HiRISE) camera. Image released Sept. 11, 2014.
Credit: NASA/JPL-Caltech/Univ. of Arizona

In September 2012, just one month after landing, Curiosity found signs of past habitability when exploring an ancient streambed that may have flowed for more than 1,000 years in the Red Planet's past.

By analyzing samples taken by Curiosity a few months later, scientists found that billions of years ago, the Martian environment — at least the one explored by Curiosity — was habitable.

Scientists have also suggested that the lake-and-stream system could have played host to simple life for millions of years. The rover, however, has not found any evidence of microbial life, and it was not designed to detect it. (A new car-size spacecraft scheduled for launch to Mars in 2020 is being crafted to look for signs of past life.)

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