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Phoenix to Try Dribbling Soil into Oven

Attempts to dislodge dirt clumped on Mars probe instrument have yet to pan out

NASA says its Phoenix Mars Lander will try a new method for sampling Martian soil after failed attempts to sift a pile of dirt on its instrument deck. Phoenix is designed to scoop up dirt and ice using a backhoe-like shovel on its nearly eight-foot (2.5-meter) robotic arm and drop various samples into eight tiny, single-use ovens. The oven openings are about the width of pencil lead; a set of screens filters out larger particles to prevent clogs. When Phoenix deposited its first sample on Friday, however, the dirt proved unexpectedly dense and none passed through the screens.

NASA announced yesterday afternoon that Phoenix vibrated its screens for 20 minutes on Sunday but only a few crumbs slipped through them. "We are going to try vibrating it one more time, and if that doesn't work, it is likely we will use our new, revised delivery method on another thermal analyzer cell," said William Boynton of the University of Arizona Lunar and Planetary Laboratory, the instrument's lead scientist. The revised method involves sprinkling dirt from the shovel, like powdered sugar on a cookie. NASA said it planned to practice the technique today and, if it works, to use it later this week to dribble grains onto the probe's microscope.

The shaking method could work, but only if the soil is relatively fine and not held together too strongly by static electricity or ice, says physicist Robert Behringer, a specialist in granular media at Duke University who is not part of the Phoenix project. "I'd incline the [shovel] and try to shake off a little bit," he says, although he notes it might require "a lot of patience."

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