The copper coin is attached to a smartphone-size plaque at the end of the robotic arm on Curiosity, NASA's Mars Science Laboratory car-size rover. The plaque, which was added to the vehicle as a calibration target, looks like an eye chart supplemented with color chips and the attached penny.The calibration plaque will be used to test the Mars Hand Lens Imager (MAHLI). The coin was selected and purchased by principal investigator Ken Edgett with Malin Space Science Systems in San Diego, CA.
"The penny is on the MAHLI calibration target as a tip of the hat to geologists' informal practice of placing a coin or other object of known scale in their photographs. A more formal practice is to use an object with [its] scale marked in millimeters, centimeters or meters," Edgett said. "Of course, this penny can't be moved around and placed in MAHLI images; it stays affixed to the rover."Apparently coins in space is not a new idea: See Gus Grissom's lost mercury dimes.