http://micro.magnet.fsu.edu/creatures/pages/marsroverdarkfield.html

We managed to capture a photograph of what are now perhaps the tiniest Martians on Mars. Appearing as an opposed duet of helmeted gladiators, these angry silicon soldiers were discovered on the surface of an image sensor used by the Spirit and Opportunity rovers sent to probe the Red planet. Maybe these are the ONLY Martians on Mars? Probably not. In any event, the chip was loaned to us by designer Mark Wadsworth who is a fan of the Silicon Zoo. Mark informs us that he decided to try his hand at silicon artwork after visiting the Zoo on several occasions. The title of his artwork is the "Dueling Marvin the Martians". Mark designed the image sensor for NASA's Jet Propulsion Laboratory along with Tom Elliot, who actually did the testing of the flight candidate imagers to select the 20 or so that actually made it on the two missions. Tom and Mark tended to butt heads quite a bit, which was the inspiration for the doodle.


The rover image sensors are charge-coupled devices (CCDs) much like those found in ordinary everyday digital cameras, but with several advanced features. In order to speed image capture, the CCD uses frame transfer technology to quickly shift the captured image behind a mask (the shielded region electronic shutter in the image below) after the photodiodes have accumulated sufficient charge (relating to the image intensity). This particular sensor contains 1024 x 1024 pixels, each of which is 12-micrometers square. The chip is a custom design that was developed to meet the rather stringent performance criteria cooked up by the mission's brainchild (Dr. S. Squyers) and his group at Cornell University.

(Lots more at site, thanks JeremyT!)