Clumpy Martian Soil Refuses to Budge
A "before" image shows a sample of Martian soil resting on a screen over the opening to one of the eight ovens of the Thermal and Evolved-Gas Analyzer instrument on Phoenix. After vibration, the soil slumped almost imperceptibly downhill.
Credit: NASA/JPL-Caltech/University of Arizona/Max Planck Institute

Efforts to jiggle a soil sample into one of the instruments on NASA's Phoenix Mars Lander were unsuccessful, mission scientists said Monday.

Scientists first attempted to deliver the first sample of Martian soil to the Thermal and Evolved-Gas Analyzer (TEGA) Saturday. The instrument is designed to heat up soil samples in its eight tiny ovens and analyze the composition of the vapors that come off of it.

Though images relayed back to Earth showed the dirt sitting on top of TEGA, detectors inside the instrument indicated that none of the soil particles had fallen through the screen at the entrance to the oven.

"What we found was that although we had an awful lot of dirt on that screen, almost none of it made it down into the oven," said TEGA co-investigator William Boynton, of the University of Arizona.

Mission scientists have said that the soil probably didn't make it through the screen, because it "appears to be quite cloddy," said mission science team member Doug Ming, of the Johnson Space Center in Houston.

The soil could be clumping together for several reasons, including the presence of salts that bind the material together or moisture in the soil that developed during landing and cemented the particles together. "We aren't sure what's actually causing this," Boynton said.

Mission controllers commanded the spacecraft to use the vibrator attached to TEGA to try to loosen the soil clumps and get the sample into the oven. However, the first try only caused a few particles to fall in, not enough to take a measurement, though the soil did move.

"You can see that the soil has actually moved, but it hasn't moved very far," Boynton said.

The clumpiness of the soil combined with the large amount of dirt delivered to the instrument seems to be keeping the sample from getting in, which Boynton noted was interesting because scientists were worried about having too little soil, not too much.

Scientists will try once more to use the vibrator to get the sample into the oven, but "we're not too optimistic that that's going to be effective," Boynton said.

Mission scientists have worked out another option though, which they call "sprinkling."

Phoenix has already scooped up a second sample, and mission controllers will use this to conduct a "sprinkle test," first over the "dumping zone" next to the lander and then over the Microscopy, Electrochemistry and Conductivity Analyzer (MECA) aboard the spacecraft. They will lower the scoop at the end of the robotic arm until it is almost level, then power up the arm's rasp (intended to scrap up samples of water ice) to vibrate the scoop and hopefully knock out the larger clumps of the Martian regolith. They will then try to tip out a small portion of the sample onto MECA.

"We really are much better off with small amounts of soil," Boynton said.

If images show that the sprinkle test was successful, controllers will have Phoenix dribble some of the sample into its optical microscope on Wednesday.

If the technique works for the microscope, they'll try it on TEGA. "If we dribble it on slowly, we'll be able to vibrate it through the screen," Boynton said.

Mission controllers were also able to confirm that a spring they photographed on the ground of the landing site came from the spacecraft, specifically from a cable on the biobarrier, which protected the robotic arm on its 422-million mile (679-million km) journey from Earth to Mars.