MANY PLANETARY SURFACE PROCESSES (LIKE PHYSICAL CHEMICAL AND ENERGETIC PARTICLE (SPACE) WEATHERING WATER ACTIVITY DIAGENESIS LOWTEMPERATURE OR IMPACT METAMORPHISM AND BIOGENIC ACTIVITY) LEAVE TRACES OF THEIR ACTIONS AS FEATURES IN THE SIZE RANGE 10S TO 100S OF MICRONS. THE MAPPING X-RAY FLUORESCENCE SPECTROMETER ( MAPX ) IS INTENDED TO PROVIDE ELEMENTAL IMAGING AT =100 MICRON SPATIAL RESOLUTION OF 2.5 X 2.5 CENTIMETER AREAS YIELDING ELEMENTAL CHEMISTRY AT OR BELOW THE SCALE LENGTH WHERE MANY RELICT PHYSICAL CHEMICAL AND BIOLOGICAL FEATURES CAN BE IMAGED AND INTERPRETED IN ANCIENT ROCKS. MAPX IS AN ARM-BASED INSTRUMENT PLACED DIRECTLY ON THE SURFACE OF AN OBJECT TO BE ANALYZED AND HELD IN REGISTRY WITH IT THROUGH THE USE OF TOUCH SENSORS THAT PHYSICALLY CONTACT THE SURFACE. DURING AN ANALYSIS EITHER AN X-RAY TUBE OR A RADIOISOTOPE SOURCE BOMBARDS THE SAMPLE SURFACE WITH X-RAYS (TUBE SOURCE) OR ALPHA-PARTICLES AND GAMMA-RAYS (RADIOISOTOPE SOURCE) RESULTING IN X-RAY FLUORESCENCE FROM THE SAMPLE. FLUORESCED X-RAYS EMITTED IN THE DIRECTION OF AN X-RAY SENSITIVE CCD IMAGER PASS THROUGH AN X-RAY 1:1 FOCUSING LENS (CALLED AN X-RAY MICRO-PORE OPTIC MPO) THAT PROJECTS A SPATIALLY RESOLVED IMAGE OF THE X-RAYS GENERATED FROM THE SAMPLE SURFACE ONTO THE CCD. THE CCD IS READ AT SEVERAL FRAMES PER SECOND SO THAT IN THE MAJORITY OF CASES NO MORE THAN ONE PHOTON STRIKES AN INDIVIDUAL PIXEL BETWEEN READ CYCLES. IN THIS WAY THE ENERGIES AND POSITIONS OF INDIVIDUAL X-RAY PHOTONS ARE RECORDED. THE IMAGES ARE STORED IN MEMORY AND PROCESSED IN REAL TIME USING ALGORITHMS PARAMETERIZED FROM THE GROUND. IN A SINGLE ANALYSIS SEVERAL THOUSAND FRAMES ARE BOTH STORED AND PROCESSED IN REAL-TIME.