It is five years since the NASA rovers named "Spirit" and "Opportunity" have been exploring Mars, sending their close up pictures and especially the microscope images.(Squyre 2004). The images (on the website http://marsrovers.jpl.nasa.gov/gallery) when studied at high magnification (250-400%) are a good source of information and capture one's attention for days on end. Often, when looking at them a second time one discovers things that were missed the first time.