The most expensive Lincoln penny in history was a 1943 copper-alloy cent that was sold for $US1.7 million in a 1996 auction. Nothing compared to this one, though. This penny is going be put on Mars for a nice $US2.5 billion. Not bad!
Of course, those $US2.5 billion are going to put a lot more stuff on Mars than just the penny. You know, like the best interplanetary robotic rover ever created by humankind.
In fact, if you take into account the total weight of Curiosity, the total cost of the penny is not that high: its 2.5 grams would only cost about $US7000. But being the first and only penny on Mars — and any other place outside Earth, as far as I know — I'm sure it would fetch a lot more than $US1.7 million at any auction.
The penny is part of the Mars Hand Lens Imager (MAHLI) camera's calibration target. The calibration target is attached to a shoulder joint of the arm that holds the camera, and contains red, green and blue colour chips, different white point chips, a "metric standardised bar graphic and a stair-step pattern for depth calibration".
The penny sits between the last two. Usually, Earth geologists use a penny to know the scale in their photographs. But why include it when you already have an accurate metric scale there? According to MAHLI Principal Investigator Ken Edgett — at Malin Space Science Systems, San Diego — it's "a tip of the hat to geologists' informal practice of placing a coin or other object of known scale in their photographs."
It was Edgett himself who bought this very special penny with his own money, just to put it on the rover. It is a 1909 "VDB" cent, "from the first year Lincoln pennies were minted, the centennial of Abraham Lincoln's birth, with the VDB initials of the coin's designer — Victor David Brenner — on the reverse." [NASA]