Washington, Oct 4 (IANS): After collecting some key samples on the Red Planet for the past four years, NASA's Curiosity rover is driving toward uphill destinations as part of its two-year mission extension that commenced from October 1.

The destinations include a ridge capped with material rich in the iron-oxide mineral hematite, about two-and-half km ahead and an exposure of clay-rich bedrock beyond that.

These are key exploration sites on lower Mount Sharp where Curiosity is currently investigating evidence of ancient, water-rich environments that contrast with the harsh, dry conditions on the surface of Mars today.

"We continue to reach higher and younger layers on Mount Sharp. Even after four years of exploring near and on the mountain, it still has the potential to completely surprise us," said Indian-origin project scientist Ashwin Vasavada from NASA's Jet Propulsion Laboratory, Pasadena, California.

Curiosity has taken more than 180,000 images since landing on Mars in August 2012.

Newly available vistas include the rover's latest self-portrait from the colour camera at the end of its arm and a scenic panorama from the colour camera at the top of the mast.

"Curiosity's assignment is the ongoing study of ancient habitability and the potential for life," said Curiosity Programme Scientist Michael Meyer from NASA.

This latest drill site -- the 14th for Curiosity -- is in a geological layer about 600 feet thick called the Murray formation.

Curiosity has climbed nearly half of this formation's thickness so far and found it consists primarily of mudstone, formed from mud that accumulated at the bottom of ancient lakes.

The findings indicate that the lake environment was enduring, not fleeting.

For roughly the first half of the new two-year mission extension, the rover team anticipates investigating the upper half of the Murray formation.

"We will see whether that record of lakes continues further," Vasavada said.

The "Hematite Unit" and "Clay Unit" above the Murray formation were identified from Mars orbiter observations before Curiosity's landing.

"The Hematite and the Clay units likely indicate different environments from the conditions recorded in older rock beneath them and different from each other. It will be interesting to see whether either or both were habitable environments," added Vasavada.

The mission is also monitoring the modern environment of Mars, including natural radiation levels.