SCIENCE GOALS AND OBJECTIVES. THE SURFACES OF ALL ATMOSPHERELESS PLANETARY BODIES INCLUDING MERCURY IS COVERED WITH A LAYER OF REGOLITH VERY SPECIFIC LOOSE HIGHLY HETEROGENEOUS MATERIAL. FORMATION MODIFICATION AND TRANSPORT OF THE REGOLITH OCCUR DUE TO COMBINATION OF METEORITIC AND MICROMETEORITIC IMPACTS AND OTHER PROCESSES. THE REGOLITH PROCESSES DEFINE SMALL SCALE INCLUDING LANDER-SCALE APPEARANCE AND PROPERTIES OF THE SURFACE. OUR KNOWLEDGE ABOUT THE REGOLITH ON MERCURY HAS BEEN LIMITED BY THE ABSENCE OF HIGH-RESOLUTION INFORMATION. THE PROPOSED PROJECT WILL USE NEW INFORMATION FROM MESSENGER MISSION TO OBTAIN ESSENTIAL KNOWLEDGE ABOUT REGOLITH ON MERCURY. IN PARTICULAR THE FOLLOWING SCIENTIFIC QUESTIONS WILL BE ADDRESSED: (1) HOW THICK IS REGOLITH ON MERCURY? IS IT INDEED THICKER THAN ON THE MOON (AS PREDICTED)? (2) ARE THERE REGIONAL VARIATIONS OF THE REGOLITH THICKNESS? IF YES HOW DO THEY CORRELATE WITH GEOLOGICAL SETTINGS? (3) IS REGOLITH GARDENING MORE INTENSIVE ON MERCURY THAN ON THE MOON (AS PREDICTED)? (4) IS DEGRADATION OF SMALL CRATERS QUICKER ON MERCURY THAN ON THE MOON? (5) HOW DOES THE EQUILIBRIUM POPULATION OF SMALL IMPACT CRATERS ON MERCURY DIFFER FROM THE LUNAR ONE? METHODOLOGY. SPECIFIC PROPERTIES OF REGOLITH ON MERCURY WILL BE ADDRESSED WITH THE FOLLOWING THREE INVESTIGATIONS ("TASKS"). TASK 1. STATISTICAL CHARACTERIZATION OF TOPOGRAPHY. THE SCALE-DEPENDENCE OF TOPOGRAPHIC ROUGHNESS WILL BE STUDIED WITH THE LASER ALTIMETER MLA DATA TO INFER THE CHARACTERISTIC SPATIAL SCALE RELATED TO SURFACE SMOOTHING BY REGOLITH GARDENING. THIS QUANTITY DEPENDS ON THE REGOLITH THICKNESS AND THE RATE OF REGOLITH GARDENING. TASK 2. MORPHOLOGIC ANALYSIS OF SMALL FRESH CRATERS. ALL MDIS IMAGES OF THE HIGHEST RESOLUTION WILL BE SYSTEMATICALLY SEARCHED FOR SMALL YOUNG IMPACT CRATERS WITH MORPHOLOGICAL SIGNS OF MECHANICALLY WEAK UPPER LAYER OF THE TARGET. REGOLITH THICKNESS AND ITS REGIONAL VARIATIONS WILL BE INFERRED FROM THESE OBSERVATIONS IN A MANNER ANALOGOUS TO THE CLASSIC WORKS. THE RESULTS WILL BE COMPARED WITH THE ANALOGOUS DATA ABOUT THE MOON. TASK 3. STATISTICAL ANALYSIS OF POPULATIONS OF SMALL CRATERS. THE HIGHEST RESOLUTION MDIS IMAGES WILL BE USED TO STUDY THE POPULATION OF SMALL CRATERS AND FIND THE EQUILIBRIUM CRATER DENSITY WHICH CONSTRAINTS THE RATES OF CRATER OBLITERATION DUE TO THE REGOLITH GARDENING PROCESSES. THE RESULTS WILL BE COMPARED WITH THE ANALOGOUS DATA ABOUT THE MOON. RELEVANCE. THE MAIN PART OF PROPOSED WORK IS PROCESSING AND DIRECT ANALYSIS OF PDS-RELEASED DATA FROM LASER ALTIMETER MLA AND CAMERA MDIS ONBOARD MESSENGER MISSION TO MERCURY A DISCOVERY MISSION EXPLICITLY LISTED IN THE DDAP CALL FOR PROPOSALS. ON THE OTHER HAND THE GOAL OF THE PROJECT IS SCIENTIFIC UNDERSTANDING OF THE REGOLITH AND RELATED PROCESSES ON MERCURY THEREFORE THE PROJECT IS A SCIENTIFIC INVESTIGATION RATHER THAN PURE DATA PROCESSING. THESE DEFINE RELEVANCE OF THE PROPOSAL TO DDAP.