Page last updated at 12:12 GMT, Tuesday, 10 June 2008 13:12 UK

Phoenix tries shake and sprinkle

Martian soil (Nasa)
The robotic arm on Phoenix needs to deliver finer particles

The clumpy nature of the soil on Mars' northern plains continues to frustrate the efforts of the Phoenix lander to carry out some of its experiments.

A sample delivered to a mini lab oven on Saturday failed to make it through a sorting screen, and attempts to vibrate the filter have had little effect.

Researchers working on the Nasa mission are now practising sprinkle motions with Phoenix's robotic scoop.

This might produce a finer-grained sample, the scientist said.

"We're going to try one more time running the vibrator," explained William Boynton, an investigator on the probe's Thermal and Evolved Gas Analyzer (TEGA).

"If that doesn't work, we're going to try sprinkling small amounts of the soil on another one of our analysers. We do have eight separate thermal analysers and we think it will be more effective if we can transfer a small amount of soil so it doesn't clog up the screen."

The purpose of the TEGA test is to bake the soil to gain some insights into its mineral make-up and possible water content.

Footpad (Nasa)
Part of the bio-barrier mechanism appears to have broken off the lander

When Saturday's load was dumped on the analyser's opening, a light trap crossing the funnel path to the oven recorded so few particles it would have been pointless to run the experiment. The initial efforts to then shake further soil down into the funnel path also had little impact.

About 20 to 30 milligrams are needed for an analysis.

"We aren't sure what's actually causing this," explained Doug Ming from Nasa's Jet Propulsion Laboratory in California.

"The soil is very clumpy. It could be due just to a very small amount of absorbed moisture, it could be due to salts in it; possibly electrostatics may be contributing as well."

Engineers have noticed an object on the ground near to one of the lander's footpads. They believe it is a spring from the bio-barrier mechanism used to cover the robotic arm and keep it clean in the latter stages of the launch campaign and during flight.

When the bio-barrier - essentially a plastic covering - was removed, it is thought the spring broke away.

Phoenix carries a meteorological station and this has continued to study Mars' weather.

Phoenix lander
The Phoenix lander carries seven science instruments

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