TUCSON, Ariz. -- NASA's Phoenix Mars Lander scientists and engineers are continuing to dig into the area around the lander with the spacecraft's robotic arm, looking for new materials to analyze and examining the soil and ice subsurface structure.

This mosaic of images shows Phoenix's workspace with the major trenches and features that have been informally named as of Sol 84 (August 19, 2008), the 84th Martian day after landing. Credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

New trenches opened recently include the "Burn Alive 3" trench in the "Wonderland" digging area in the eastern portion of the arm's reachable workspace. Researchers choose such names informally to aid discussion.

The team is excavating one side of Burn Alive 3 down to the ice layer and plans to leave about 1 centimeter (0.4 inch) of soil above the ice on the other side. This intermediate depth, located a couple centimeters (0.8 inch) above the Martian ice-soil boundary, gives the science team the vertical profile desired for a sample dubbed "Burning Coals," intended to be the next material delivered to Phoenix's Thermal and Evolved Gas Analyzer (TEGA).

The surface of the ground throughout the arctic plain where Phoenix landed is patterned in polygon shapes like those of permafrost areas on Earth, where the ground goes through cycles of swelling and shrinking. Some of the recent and planned digging by Phoenix takes advantage of landing within arm's reach both of the centers of polygons and the troughs between polygons. For example, the "Stone Soup" trench has been dug in a trough in the "Cupboard" excavation area, near the western end of the arm's workspace. The team plans to dig in this zone as deep as possible to study properties of the soil and ice deep in a polygon trough.

A sample from the Cupboard area may be delivered to the lander's wet chemistry lab, part of the Microscopy, Electrochemistry and Conductivity Analyzer (MECA). The location for obtaining a sample would depend on results from further digging in "Upper Cupboard," and use of the thermal and electrical conductivity probe on the arm, inserted into icy soil within Upper Cupboard to test for the presence of salts.

In addition, Phoenix's robotic arm would acquire ice-rich soil from "Upper Cupboard" and observe the material in the arm's scoop to determine whether the sample sublimates. Melting is an indication of the presence of salt. If the sample melts and leaves behind a salty deposit, "Upper Cupboard" would be the location for the next sample for the wet chemistry lab. If no salts are detected, the team would continue with plans to use the "Stone Soup" trench for acquiring the next wet chemistry lab sample.

"We expect to use the robotic arm heavily over the next several weeks, delivering samples to our instruments and examining trench floors and walls to continue to search for evidence of lateral and vertical variations in soil and ice structures," said Ray Arvidson, Phoenix's "dig czar," from Washington University in St. Louis.

The Phoenix science and engineering teams have transitioned to "Earth time," with the teams working a parallel daytime shift not tied to the current time on Mars. Daily activities are being planned for the spacecraft as the lander performs activities that were sent up the previous day. Digging and documenting are done on alternate days to allow the science team time to analyze data and adjust activities accordingly.

In upcoming sols, the team plans to scrape the "Snow White" trench and experiment with acquiring and holding samples in the shade versus the sun. They want to find out if prolonged exposure to sunlight causes the acquired material to stick to the scoop, as has occurred with previous samples.

The Phoenix mission is led by Peter Smith of The University of Arizona with project management at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and development partnership at Lockheed Martin, located in Denver. International contributions come from the Canadian Space Agency; the University of Neuchatel; the universities of Copenhagen and Aarhus, Denmark; Max Planck Institute, Germany; and the Finnish Meteorological Institute.