NASA's Phoenix closes on Red Planet

Arctic touch-down on 25 May

NASA has adjusted the flight path of its Phoenix Mars Lander, en route to a planned touch-down on the Red Planet on 25 May, on its mission to explore the body's Arctic plain.

The agency has "conditionally approved" a roughly 62 mile by 12 mile (100km by 20km) "landing ellipse" in an area dubbed "Green Valley", which lies at approximately 68 degrees N, 233 degrees E, having scoured High Resolution Imaging Science Experiment (HiRISE) images of the area for potential hazards.

NASA explains that the camera has snapped "more than three dozen images of the area" and that "analysis of those images prompted the Phoenix team to shift the centre of the landing target 13km (8 miles) southeastward, away from slightly rockier patches to the northwest".

Accordingly, the Phoenix navigation team at NASA's Jet Propulsion Laboratory in Pasadena yesterday carried out a trajectory adjustment by "pivoting Phoenix 145 degrees to orient and then [firing] spacecraft thrusters for about 35 seconds, then pivoting Phoenix back to point its main antenna toward Earth".

Phoenix's landing will be a nail-biter for the NASA team. Researchers have identified five million rocks in and around the eclipse "each big enough to end the mission if hit by the spacecraft during landing".

JPL's David Spencer, Phoenix deputy project manager, said: "The environmental risks at landing - rocks and slopes - represent the most significant threat to a successful mission. There's always a chance that we'll roll snake eyes, but we have identified an area that is very flat and relatively free of large boulders."

Of the touch-down, NASA adds: "In the final seven minutes of its flight on 25 May, Phoenix must perform a challenging series of actions to safely decelerate from nearly 21,000km/h (13,000mph). The spacecraft will release a parachute and then use pulse thrusters at approximately 914 metres (3,000 feet) from the surface to slow to about 8km/h (5mph) and land on three legs."

Once safely down, Phoenix will "dig to an ice-rich layer expected to lie within arm's reach of the surface and analyse the water and soil for evidence about climate cycles and investigate whether the environment there has been favorable for microbial life".

Peter Smith, principal mission investigator at the University of Arizona, explained: "Our landing area has the largest concentration of ice on Mars outside of the polar caps. If you want to search for a habitable zone in the arctic permafrost, then this is the place to go."

Phoenix packs an arsenal of mission instruments - Surface Stereo Imager; Robotic Arm Camera; Mars Descent Imager; Thermal and Evolved Gas Analyzer; Microscopy, Electrochemistry, and Conductivity Analyser; Wet Chemistry Experiment; Microscopy, including the Optical Microscope and the Atomic Force Microscope; Thermal and Electrical Conductivity Probe; and Meteorological Station - designed to achieve it's two principal "bold objectives" to "study the history of water in the Martian arctic" and "search for evidence of a habitable zone and assess the biological potential of the ice-soil boundary".

There's more on the mission's science at the University of Arizona. ®

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