By Irene Klotz

CAPE CANAVERAL, Fla., July 29 (Reuters) - NASA's Mars rover was on its final approach to the red planet on Sunday, heading toward a mountain that may hold clues about whether life has ever existed on Mars, officials said.

The rover, also known as Curiosity, has been careening toward Mars since its launch in November. The nuclear-powered rover the size of a compact car is expected to end its 352-million-mile (567-million-km) journey on Aug. 6 at 1:31 a.m. EDT (0531 GMT).

The landing zone is a 12-mile-by-4-mile (20-km-by-7-km) area inside an ancient impact basin known as Gale Crater, located near the planet's equator. The crater, one of the lowest places on Mars, has a 3-mile-high (5-km-high) mountain of what appears to be layers of sediment.

Scientists suspect the crater may have once been the floor of a lake.

If so, they believe that sediments likely filled the crater, but were carried away over time, leaving only the central mound.

Readying to travel the last stretch to its landing site, Curiosity fired its steering thrusters for six seconds early Sunday, tweaking its flight path by 0.4 inches (1 centimetre) per second.

"I will not be surprised if this was our last trajectory correction maneuver," chief navigator Tomas Martin-Mur, with NASA's Jet Propulsion Laboratory in Pasadena, California, said in a statement.

Curiosity is expected to hit the top of the Martian atmosphere at 1:24 a.m. EDT (0524 GMT) on Aug. 6. If all goes as planned, seven minutes later the rover will be standing on its six wheels on the dry, dusty surface of Mars.

Landing is by no means guaranteed. To transport the one-ton rover and position it near the mound, engineers devised a complicated system that includes a 52-foot (16-metre) diameter supersonic parachute, a rocket-powered aerial platform and a so-called "sky crane" designed to lower the rover on a tether to the ground.

NASA last week successfully repositioned its Mars-orbiting Odyssey spacecraft so that it would be able to monitor Curiosity's descent and landing and radio the information back to ground controllers in as close to real time as possible.

Earth and Mars are so far apart that radio signals, which travel at the speed of light, take 13.8 minutes for a one-way journey. (Editing by Kevin Gray and Mohammad Zargham)

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    This artist's concept depicts the rover Curiosity, of NASA's Mars Science Laboratory mission, as it uses its Chemistry and Camera (ChemCam) instrument to investigate the composition of a rock surface. ChemCam fires laser pulses at a target and views the resulting spark with a telescope and spectrometers to identify chemical elements. The laser is actually in an invisible infrared wavelength, but is shown here as visible red light for purposes of illustration.

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    The Atlas V 541 vehicle was selected for the Mars Science Laboratory mission because it has the right liftoff capability for the heavy weight requirements of the rover and its spacecraft.

  • Mars Science Laboratory Spacecraft During Cruise

    This is an artist's concept of NASA's Mars Science Laboratory spacecraft during its cruise phase between launch and final approach to Mars. The spacecraft includes a disc-shaped cruise stage (on the left) attached to the aeroshell. The spacecraft's rover (Curiosity) and descent stage are tucked inside the aeroshell.

  • Curiosity Approaching Mars

    The Curiosity rover is safely tucked inside the spacecraft's aeroshell. The mission's approach phase begins 45 minutes before the spacecraft enters the Martian atmosphere. It lasts until the spacecraft enters the atmosphere.

  • Curiosity Inside Aeroshell

    The Curiosity rover and the spacecraft's descent stage are safely tucked inside the aeroshell at this point. The aeroshell includes a heat shield (on the right, facing in the direction of travel through the atmosphere) and backshell. The diameter of the aeroshell is 14.8 feet (4.5 meters), the largest ever used for a mission to Mars.

  • Mars Science Laboratory Guided Entry At Mars

    The mission's entry, descent, and landing (EDL) phase begins when the spacecraft reaches the top of Martian atmosphere, about 81 miles (131 kilometers) above the surface of the Gale crater landing area, and ends with the rover safe and sound on the surface of Mars. During the approximately seven minutes of EDL, the spacecraft decelerates from a velocity of about 13,200 miles per hour (5,900 meters per second) at the top of the atmosphere, to stationary on the surface.

  • Deceleration of Mars Science Laboratory in Martian Atmosphere

    This artist's concept depicts the interaction of NASA's Mars Science Laboratory spacecraft with the upper atmosphere of Mars during the entry, descent and landing of the Curiosity rover onto the Martian surface.

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    This is an artist's concept of the Mars Science Laboratory Curiosity rover parachute system.

  • Curiosity While On Parachute

    This is an artist's concept of NASA's Curiosity rover tucked inside the Mars Science Laboratory spacecraft's backshell while the spacecraft is descending on a parachute toward Mars. The parachute is attached to the top of the backshell. In the scene depicted here, the spacecraft's heat shield has already been jettisoned.

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    This is an artist's concept of the rover and descent stage for NASA's Mars Science Laboratory spacecraft during the final minute before the rover, Curiosity, touches down on the surface of Mars.

  • Curiosity's Sky Crane Maneuver

    The entry, descent, and landing (EDL) phase of the Mars Science Laboratory mission begins when the spacecraft reaches the Martian atmosphere, about 81 miles (131 kilometers) above the surface of the Gale crater landing area, and ends with the rover Curiosity safe and sound on the surface of Mars.

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    This artist's concept depicts the moment that NASA's Curiosity rover touches down onto the Martian surface.

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    This artist's concept depicts the moment immediately after NASA's Curiosity rover touches down onto the Martian surface.

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    This artist concept features NASA's Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life.

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  • Mars Rover Curiosity

    This artist concept features NASA's Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life.