This is a photo of an engineering model of the Thermal and Evolved-Gas Analyzer (TEGA) instrument on board NASA's Phoenix Mars Lander. This view shows a TEGA oven-loading mechanism beneath the input screen. The screen on the 1-and-1/2-inch-wide funnel has been removed in this model to show the whirligig that is suspended from the screw on the shaft. The black hole underneath is the porthole that leads to the oven.

A tiny electric current compresses and releases a spring on the shaft. As the shaft spins, the screw bumps the screen, breaking up clumps of material into fine particles so they pass through the one millimeter-square screen openings. The energy applied to the tapping screen is about 0.02 inch per pound, or the force needed to move a one-pound mass two-hundredths of an inch.

The screw also lifts the three-bladed whirligig so that it jostles fine particles and keeps the oven port open to aid the loading process.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Photojournal Note: As planned, the Phoenix lander, which landed May 25, 2008 23:53 UTC, ended communications in November 2008, about six months after landing, when its solar panels ceased operating in the dark Martian winter.