The piece of metal with the American flag on it in this image of a NASA rover on Mars is made of aluminum recovered from the site of the World Trade Center towers in the weeks after their destruction. The piece serves as a cable guard for the rock abrasion tool on NASA's Mars Exploration Rover Spirit as well as a memorial to the victims of the Sept. 11, 2001, attacks. An identical piece is on the twin rover, Opportunity.

The rock abrasion tools were built by Honeybee Robotics in lower Manhattan, less than a mile from the site.

This image comes from the panoramic camera on Spirit and was taken on Feb. 2, 2004, the 30th Martian day, or sol, of Spirit's work on Mars. Both Spirit and Opportunity completed their prime missions in April 2004 and began years of additional work in extended missions. Both rovers have made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life. Spirit ended communications in March 2010. Opportunity is still active, and researchers plan to use its rock abrasion tool on selected targets around a large crater that the rover reached last month.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for the NASA Science Mission Directorate, Washington.