[Relax]

The stamp which commemorates the historic Mars Pathfinder mission has been considered the largest American stamp.

The Mars Pathfinder stamp is the third U.S. stamp subject to incorporate hidden images to prevent counterfeiting, while adding an interesting design element. The hidden text -- Mars Pathfinder, July 4, 1997 and the letters USPS --is not visible to the naked eye but can be viewed by using a decoder lens, which is available through the Postal Service's Philatelic Fulfillment Center in Kansas City, MO. The U.S. Air Force and Classic Movie Monsters stamps issued earlier this year also feature hidden images.

Since its Independence Day landing, Pathfinder has returned 2.6 billion bits of information, including more than 16,500 images, as well as chemical analyses of rocks and extensive data on winds and other weather factors. After operating on the surface of Mars three times longer than expected, the mission began winding down last week as daily communications with the lander and rover were officially halted.