Why is NASA sending a penny to Mars?
A US penny is on-board NASA's Curiosity rover that is scheduled to land on Mars in August. The 1909 penny commemorating the centennial of President Lincoln's birth will act as a calibration target to help scientists and the public to gauge the size of objects on Mars.
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"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."Skip to next paragraph
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The middle of the target offers a marked scale of black bars in a range of labeled sizes. While the scale will not appear in the photos that MAHLI takes of Martian rocks, knowing the distance from the camera to a rock target will allow scientists to correlate calibration images to each of the investigation images. [Amazing Photos of Mars]
Another part of MAHLI's calibration target plaque displays six patches of pigmented silicone as aids for interpreting color and brightness in images. Five of them – red, green, blue, 40-percent gray and 60-percent gray – are spares from targets on NASA's Mars Exploration Rovers Spirit and Opportunity, which landed on the Red Planet in 2004.
The sixth square, with a fluorescent pigment that glows red when exposed to ultraviolet light, allows verification of an ultraviolet light source on MAHLI.
A stair-stepped area at the bottom of the target, plus the penny, will help with three-dimensional calibration using known surface shapes.
A penny for the public's thoughts
Accompanying the penny on the MAHLI calibration target is a tiny cartoon of a character named "Joe the Martian." Both the coin and the character serve double duty: both are calibration targets and both are intended to engage the public.
"Everyone in the United States can recognize the penny and immediately know how big it is, and can compare that with the rover hardware and Mars materials in the same image," Edgett said. "The public can watch for changes in the penny over the long term on Mars."
"Will it change color? Will it corrode? Will it get pitted by windblown sand?" Edgett said.
The Joe the Martian character is taken from a children's science periodical, "Red Planet Connection," where it was regularly seen when Edgett directed the Mars outreach program at Arizona State University, Tempe, in the 1990s.
Joe was created earlier, as a part of Edgett's schoolwork when he was 9 years old and NASA's Viking missions, launched in 1975, inspired him to dream of becoming a Mars researcher.
"The Joe the Martian on Curiosity really is a 'thank you' from the MAHLI team to the folks who have provided us with the opportunity to study Mars, the U.S. taxpayers," Edgett said. "He's also there to encourage children around the world to set goals that will help them achieve their dreams in whatever interests they pursue."