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A NASA rover plunged through the atmosphere of Mars and bounced down upon its rocky surface Saturday night(American time), beginning a mission to roam the Red Planet in search of evidence that it was once suitable for life.

An image from NASA television shows control room worker pointing to the screen as a panoramic polar projection image of the Mars Exploration Rover spacecraft taken from the surface of Mars after it landed successfully January 3, 2004. [AP]

Radio signals received on Earth minutes after the landing suggested the Spirit rover survived, prompting mission controllers at NASA's Jet Propulsion Laboratory to let out whoops of delight.

It still was not immediately known if the Spirit rover would operate as planned. It is one of two-identical six-wheeled robots expected to roam the planet for 90 days, analyzing Martian rocks and soil for clues that could reveal whether the planet was ever a warmer, wetter place capable of sustaining life.

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

It was not immediately clear if the air bags sufficiently protected the rover, enclosed inside a four-petaled lander, from the jarring landing.

But up until the landing everything was proceeding flawlessly, with Spirit appearing on track to make a "bull's-eye" landing within a cigar-shaped ellipse inside Gusev Crater, a Connecticut-sized indentation just south of the Martian equator, navigation team chief Louis D'Amario said.

NASA Administrator Sean O'Keefe, left, hugs Principal Investigator Steve Squyres in the control room at NASA's Jet Propulsion Laboratory as they get a signal from the Mars Rover Spirit after it landed, Saturday, Jan. 3, 2004, in Pasadena, Calif. [AP]

"This is essentially perfect navigation. We couldn't have possibly hoped to do better than this," D'Amario said.

Previously, about two of every three attempts to land spacecraft on Mars have failed. 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.

"It's an incredibly difficult place to land. Some have called it the 'death planet' for good reason," said Ed Weiler, NASA's associate administrator for space science.

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.

"We have done everything we know to do to ensure these missions will be a success," said Charles Elachi, director of the National Aeronautics and Space Administration's Jet Propulsion Laboratory.

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

The camera- and instrument-laden rovers were designed to spend 90 days analyzing Martian rocks and soil for clues that could reveal whether the Red Planet was ever a warmer, wetter place capable of sustaining life.

Today, Mars is a dry and cold world. But ancient river channels and other water-carved features spied from orbit suggest that Mars may have had a more hospitable past.

"We see these intriguing hints Mars may have been a different place long ago," Squyres said.

The rovers were built to look for evidence that liquid water — a necessary ingredient for life — once persisted on the surface of the planet. A direct search for life on Mars is at least a decade away, NASA scientists said.

Together, the twin robots were launched in the most intensive scientific assault on another planetary body since the Apollo missions to the moon, said Orlando Figueroa, director of NASA's Mars exploration program.

NASA launched the 384-pound Spirit and its twin in hopes they would become the fourth and fifth U.S. spacecraft to survive landing on Mars. Twenty other spacecraft from various nations have failed.

Scientists are taking advantage of the closest approach Mars has made to Earth in 60,000 years. NASA intends to send spacecraft to Mars at regular 26-month intervals, or each time the Earth laps the Red Planet as they both circle the sun.

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

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