The Phoenix lander's search for organic evidence of past or present life on Mars will begin in earnest around July 7 as the spacecraft's organic chemistry instrument is fed a sample of 100 percent water ice.

The Phoenix team also wants to do ice sampling as early as possible in the event an electrical short in the device prematurely halts organic oven operations. This marks a major shift in mission emphasis from the general characterization of the landing site, to specific focused testing of ice and the soil/ice interface region.

The shift to ice is being done for "good news" and "bad news" reasons. The good news is the robotic arm has finally uncovered and prepared a large area of ice near the lander that makes such sampling possible

The bad news is there is some urgency because of lingering concerns about an electrical short in the Thermal and Evolved Gas Analyzer (TEGA) organic chemistry instrument (AW&ST June 30 pg. 37).

The short developed when the instrument's soil screen shaker mechanism was operated several times to break up clumpy soil that initially would not fall into the oven earlier (Aerospace DAILY, June 26).

Now the objective is to obtain a guaranteed ice sample in case the short worsens and TEGA dies. "We are operating as if this might be the last sample we can get into the TEGA instrument," a Phoenix manager said.

The move boils down to conservative sample planning because managers also believe the instrument could continue to work fine. But they are hedging their bets since a key factor is the fact that the shaker mechanism always operates when TEGA takes in a sample, as it will do with the ice, and shaking can worsen the short circuit.

NASA's Jet Propulsion Laboratory, Lockheed Martin and University of Arizona engineers are assessing the engineering options to ensure continued TEGA operations.

Phoenix image of 'Snow White' trench: NASA/JPL-Caltech/University of Arizona/Max Planck Institute