WASHINGTON, Jan. 3 (Xinhuanet) -- A NASA rover designed to search for signs of life on Mars arrived safely on Saturday night after an almost seven-month space journey.

    The spacecraft carrying the Spirit rover made its touchdown on the Red Planet known by sending back a series of tones to scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

    The rover relied on a heat shield, parachute and rockets to slow its descent to Mars. Eight seconds before landing, a giant set of airbags inflated to cushion its bouncy landing.

    "Since the spacecraft plunged into the Martian atmosphere, it has been fully controlled by itself," JPL Telecommunications and Mission System Manager Peter Poon told Xinhua.

    As Mars is over 487 million km far from Earth, transmitting a signal between the two planets takes around nine minutes.

    After landing, the Spirit rover will spend more than a week testing instruments before it starts to move. NASA hopes to have pictures from Spirit by Sunday.

    If all goes as planned, the golf cart-sized robot aboard Spirit,which is crammed with cameras and scientific instruments designed to study the geologic record of Mars, will roam the planet for evidence of water, a necessary ingredient for life.

    The 820-million-dollar NASA project also includes a twin rover, Opportunity, which is set to arrive on Mars on Jan. 24.

    The pair are expected to take tens of thousands of pictures andanalyze soil samples for three months before they run out of power.The images, from the microscopic to the panoramic, should reveal the planet with unprecedented clarity.

    The clearest and most detailed pictures of Mars should come from the color panoramic camera atop a mast rising from each rover.Its resolution will be three times greater than that of any other camera ever sent to the surface of Mars. Scientists plan to use those sweeping images to pinpoint which rocks would be investigated.

    In 1997, the NASA's Pathfinder spacecraft transmitted to Earth more than 16,000 pictures. Spirit and Opportunity could take threetimes as many pictures as Pathfinder.

    Since 1971, there have been 13 landing attempts, but only threeprobes -- Viking 1 and Viking 2 in 1976 and Pathfinder in 1997 -- have successfully landed on Mars. The latest apparent failure was the British Beagle 2 lander, which has not been heard from since it was to have set down on Mars on Christmas Day.

    NASA's last attempt at landing on Mars, in 1999, failed when a software glitch sent the Polar Lander crashing to the ground. Since then, the space agency has increased oversight of its missions.

    The Spirit landing follows another important American space mission. On Friday, a NASA spacecraft flew through the bright haloof a distant comet to scoop up less than a thimbleful of dust thatcould shed light on how the solar system was formed. Enditem