When NASA sent their Mars Science Laboratory (nicknamed Curiosity) to Mars in 2011, they included one unexpected object: a 1909 VDB Lincoln wheat cent. The penny was included on the mission as one of several calibration targets for the Mars Hand Lens Imager camera (MAHLI.)
R. Aileen Yingst, deputy principal investigator for the MAHLI camera, stated that at 14 micrometers per pixel, the photo of the penny was a demonstration of the imager’s best-capable return. This photo demonstrated that the camera was functioning as intended for close-up views of small objects on the Martian surface.
The penny, along with another target, helps the camera with three-dimensional calibration. According to Space.com, MAHLI principal investigator Ken Edgett bought the VDB penny himself, to continue an old geology tradition. “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.” It also provides a familiar object for the general public to watch for in images from the rover.
Interestingly, the penny collected Martian dust during the 14 months between landing and the taking of the photo, despite being mounted vertically on the rover. This not only produces a more interesting picture of the coin, but gives NASA scientists additional information about how Martian dust behaves.
You really never know where a VDB cent will turn up!