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By Irene Klotz

PASADENA, Calif., May 25 (Reuters) - A small science probe blazed through the salmon-colored skies of Mars on Sunday, touching down on a frozen desert at the planet's north pole to search for water and assess conditions for sustaining life, NASA officials said.

The spacecraft, known as Phoenix, landed at 4:53 p.m. PDT (7:53 p.m. EDT/2353 GMT) after a do-or-die plunge through the planet's thin atmosphere and thruster-jet landing to the Mars surface. It marked the first time that a spacecraft had successfully landed at one of the planet's polar regions.

"It was a hell of a lot scarier than the two Mars rovers," NASA's space sciences chief Ed Weiler said, referring to the cushioned landings of the Spirit and Opportunity rovers. "I kept thinking, 'I wish I had airbags.'"

Pulled by Mars' gravity, Phoenix was tearing along at 12,700 mph (20,400 kph) before it entered the atmosphere, which slowed the craft so it could pop out a parachute and fire thruster rockets to gently float to the ground.

"It's down, baby, it's down!," yelled a NASA flight controller, looking at signals from Mars showing that Phoenix had landed.

Flight controllers and scientists battled nerves as Phoenix wrapped up its 10-month, 423 million-mile journey. In 14 minutes, the probe transformed from an interplanetary cruiser to a free-standing science station.

"People got really uncomfortable," said Doug McCuistion, director of the Mars Exploration Program at the Jet Propulsion Laboratory in Pasadena, which oversees the mission.

Scientists found in 2002 that Mars' polar regions have vast reservoirs of water frozen beneath a shallow layer of soil. Phoenix was launched Aug. 4, 2007, to sample the water and determine if the right ingredients for life are present.

NASA attempted a landing on Mars' south pole in 1999, but a problem during the final minutes of descent ended the mission.

The U.S. space agency canceled its next Mars lander but successfully dispatched Spirit and Opportunity to the planet's equatorial region to search for signs of past surface water.

Phoenix was created out of spare parts from the failed Polar Lander mission and the mothballed probe. Unlike the rovers, Phoenix did not bounce to the planet's surface in airbags, which are not suitable for larger spacecraft.

Instead, like the 1970s-era Viking probes and the failed Polar Lander mission, it used a jet pack to lower itself to the ground and fold-out legs to land on.

"We haven't landed successfully on legs and propulsive rockets in 32 years," Weiler said. "When we send humans there, women and men, they're going to be landing on rockets and legs, so it's important to show that we still know how to do this."

(Editing by Dan Whitcomb and Doina Chiacu)

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