Testing at NASA's Jet Propulsion Laboratory in August 2009 is assessing possible maneuvers that the Mars rover Spirit might use for escaping from a patch of soft soil where it is embedded at a Martian site called "Troy." In this image from Aug. 21, 2009, members of the rover team at JPL plan for starting to use a second rover in the test setup.

The second rover, called the Surface System Testbed Lite (far right) is lighter weight than the primary engineering test rover, called the Surface System Testbed (left foreground). The lighter version does not carry a science payload and robotic arm, as Spirit, Opportunity and the Surface System Testbed do.

Making comparisons between motions of the two test rovers in duplicated drives will aid the rover team in interpreting effects of differing gravity on rover mobility. An object that weighs 10 pounds on Earth weighs just 3.8 pounds on Mars, due to the smaller mass of Mars compared to Earth.

To see updates on the efforts to free the Spirit rover, visit the JPL Free Spirit website.