Scientists working on Nasa's Phoenix Lander on Saturday were trying to find out why a soil sample dropped on to an instrument bay was not registered. They were trying to determine what could have prevented the Martian soil, picked by the Phoenix lander's robot arm, from reaching a tiny testing oven.

The Images sent back from Mars were showing the sample lying across a screen protecting the opening to a tiny oven. The scientists were opining that the soil might have been too lumpy to pass through into the Thermal and Evolved-Gas Analyzer, which was to bake the soil to gain some insights into its possible water content and mineral make-up.

Actually, the 2.4m-long robot arm delivered the sample to Phoenix's onboard laboratory. The screen that covered the entrance to the analyzer was designed to let through only particles that were smaller than one millimetre, to stop a funnel leading to the tiny oven becoming clogged with larger fragments. What went wrong was that the infrared beam crossing the pathway failed to register any material falling through the funnel, suggesting none of the sample material made it into the analyzer.

Ray Arvidson, of Washington University in St Louis, said, "I think it's the cloddiness of the soil and not having enough fine granular material.” He explicated, "In the future, we may prepare the soil by pushing down on the surface with the arm before scooping up the material to break it up, then sprinkle a smaller amount over the door.”

Phoenix, which landed on Mars' northern plains on 25 May, will spend the next three months investigating its landing location for signs that life could ever have found the conditions there habitable.