I'm surprised that I've never heard of this until today. There is metal from the World Trade Center on Mars!
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.