Get ready to pull out a fascinating piece of space trivia to wow your friends at your next party. There’s a 1909 Lincoln-head penny on Mars, and it has an important job to do. NASA’s Curiosity Rover has been exploring the Gale Crater on the red planet since 2012 and the penny has been along for the ride.
NASA dropped a reminder about the penny on X on March 21 along with an explanation of why it’s there. “This is a 1909 Lincoln penny, and it’s part of the calibration target for my MAHLI instrument,” the rover team tweeted. “The penny is a nod to a geology tradition, where an object of known scale is used as a size reference for close-up photos of rocks and soil.”
MAHLI’s full name is Mars Hand Lens Imager. It functions a lot like a hand-held magnifying lens, the kind a human geologist would use on Earth. It can take close-up images of the Martian surface to highlight details of rocks and other landscape features. MAHLI is located on the end of Curiosity’s extendable arm.
NASA could have picked any penny from any year, but the 1909 penny has special significance. That was the first year for Lincoln pennies and it also marked 100 years after Abraham Lincoln’s birth.
The penny isn’t alone on the calibration target. Note the stair-step pattern above it. “MAHLI can provide three-dimensional information by taking a series of images at different focal ranges or by moving the camera between two images to yield stereo-pair images,” said NASA in an explainer. “The stair-step pattern at the bottom of the target, plus the penny, help with three-dimensional calibration using known surface shapes.”
There’s a hidden treat just below the black-and-white pattern: a tiny line drawing of a cartoon figure. It’s shaped like a blob with arms and legs and antennae. That’s Joe the Martian. Joe has a history as a public outreach mascot for communicating Mars science to children.
There’s one more important piece to the calibration target. What looks like a palette of watercolors at the top is actually pigmented silicone. Those rectangles help researchers work out the color and brightness of objects imaged by MAHLI.
The Lincoln penny is also a marker of change on Mars. Curiosity has weathered dust storms, brutal cold and rocky landscapes. The penny reflects that journey. It was clean when it arrived and has since shown the impacts of time and dust on the mission. “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?” said Curiosity project scientist Ken Edgett back before the rover mission reached Mars in 2012.
MAHLI zoomed in on the penny in late 2023 and revealed a dust-covered Lincoln, but with the words still legible despite the powdery coating. Pennies survive countless pockets and wear and tear on Earth, so perhaps it’s not surprising to see one handling the rough conditions on Mars.
Curiosity is working to understand whether or not Mars might have been habitable for microbial life in the past. The long-lived rover has uncovered information about the history of water in Gale Crater and spotted evidence of organic material, though the origin of those molecules is uncertain. The rover’s Lincoln penny may have lost its shine, but it seems to still be giving Curiosity plenty of luck on its continuing mission.
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