After running into trouble collecting samples of Martian soil, the Pheonix lander will try to use its robotic arm on Tuesday to sprinkle small amounts of soil on the lander's science instruments.

On Saturday, Phoenix unloaded a scoopful of Martian soil on the first of eight compartments on the spacecraft's Thermal and Evolved-Gas Analyzer (TEGA) instrument. But sensors indicated little soil reached its target – a tiny cylindrical oven designed to heat up the soil to analyse its composition.

A screen above the instrument was supposed to filter small bits of soil so it could be funnelled into the oven. But the lander's first scoop may have been too heavy to get through the 1 mm-wide openings in the screen.

"It looks like we got much more soil than we're use to working with, and it might just have clogged the screens," said TEGA co-investigator William Boynton of the University of Arizona in Tucson, US, at a press conference on Monday.

Dribbling in small amounts of soil into the next TEGA compartment might be able to circumvent this problem, a feat team members may try on Tuesday.

Fall through

Their plan is to turn on an instrument on the underside of the scoop that is designed to grind up ice. That will produce vibrations that could drive larger clumps of soil to the top of the scoop – the way shaking a cereal box causes smaller crumbs to fall to the bottom of the box.

Then, the lander's arm will tilt the scoop – in small steps – to try to unload the larger clumps, before sprinkling the remaining soil in the instrument.

Each TEGA screen is at a 45° angle, so dropping a small bit of soil on the highest point of the screen may allow some fine soil particles to separate out on the incline and fall through to the oven.

The results of the 'sprinkle test' may arrive as early as Tuesday, says Doug Ming of NASA's Johnson Space Center in Houston, Texas, US.

Small shift

After Saturday's delivery, some Phoenix mission members speculated that a vibrator inside the first TEGA compartment, designed to knock small bits of soil into the oven, might not be functioning.

But photos of the trap doors released on Monday suggest the vibrator did shift the soil, though little entered the oven.

"The soil has actually moved, but it hasn't moved very far," said Boynton. Large clumps of the soil, combined with the large overall size of the scoop, may be weighing on the vibrator and preventing it from separating out the sub-millimetre-sized particles that are needed.

Part of the problem seems to be the soil, which seems to exhibit an unusual level of clumpiness. Researchers are not quite sure why the clumps exist, but they suggest a small amount of moisture, salt, or even some electrical interaction between soil particles may be responsible.

The lander has already gathered a new scoop of soil, which it will try to sprinkle slowly on top of another instrument, the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA), which holds several microscopes and a wet chemistry laboratory.

Mars Rovers - Mars is full of surprises, learn more in our continually updated special report.

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