Original Source: BBC News

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The Phoenix lander is due to touch down on Monday in the far north of the Red Planet, after a 423-million-mile journey from Earth. The probe is equipped with a robotic arm to dig for water ice thought to be buried beneath the surface. Scientists say the mission should give the clearest indication yet of whether Mars could once have harbored life.

The final seven minutes of the probe's ten-month journey is regarded as the riskiest part of the mission. After it enters the top of the Martian atmosphere at nearly 5.7km/s (13,000 mph), the probe must perform a series of maneuvers to come safely to rest. It will release a parachute, use pulsed thrusters to slow to a fast walking speed, then come to a halt on three legs. If all goes to plan, the Phoenix lander will reach the surface of Mars at 0053 BST (1953 EDT) on May 26. Nasa controllers will know in about 15 minutes whether the attempt has been successful.

Landing on Mars is a notoriously tricky business. Of the 11 missions that have tried to land probes on Mars since 1971 - only five have succeeded. Phoenix is an apt name for the current mission, as it rose from the ashes of two previous failures. In September 1999, the Mars Climate Orbiter spacecraft crashed into the Red Planet following a navigation error caused when technicians mixed up "English" (imperial) and metric units. A few months later, another Nasa spacecraft, the Mars Polar Lander (MPL), was lost near the planet's South Pole. Phoenix uses hardware from an identical twin of MPL, the Mars Surveyor 2001 Lander, which was cancelled following the two consecutive failures. The probe was launched on 4 August 2007 on a Delta II rocket from Cape Canaveral Air Force Station in Florida.

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