When the Curiosity rover landed on Mars more than a year ago it brought with it an earthly artifact more than a century old – a 1909 Lincoln penny. For good luck? Maybe, but JPL engineers affixed the penny to the roving robot as a calibration target for its mobile, closeup camera named MAHLI (Mars Hand Lens Imager). While Abe’s looking a little dusty, his weathered face tells the story of 14 months on another planet.
For MAHLI’s closeup pictures to accurately portray colors and brightness of the Martian landscape it needs a reference. The colored patches allow MAHLI to “white balance” or neutralize color casts common in digital images. The penny is a nod to the common practice by geologists of placing an object of known size in the frame to give the viewer a sense of scale.
Without something familiar in a picture as a reference, it’s hard to know the dimensions of things like soil grains and Mars pebbles.
Ken Edgett, principal investigator for MAHLI, bought the penny with his own money (coins in similar condition go for around $20 on eBay). Sure, mission planners could have used a standard ruler scale but opted instead for Edgett’s more poetic penny. NASA’s willingness to bend standard procedure to better connect with the public is a good thing.
But why a 1909 penny in particular? The Lincoln cent was first minted in 1909 to commemorate the centennial of President Lincoln’s birth. Curiosity was originally scheduled to launch in 2009, which happened to be the penny’s 100th anniversary. The connections across 200 years of time have an irresistible appeal to our romantic side.
Delays pushed Curiosity’s launch date to 2011, but Lincoln kept his seat and now looks out across new territory every day.
The penny’s shine has disappeared beneath a fine coating of dust and bits of soil. I imagine NASA scientists wringing crucial data about the Martian atmosphere, winds and soil particle size as they study of the deposition of material on the coin’s face now and in the years ahead. Lincoln’s legacy reaches even to the Red Planet.