GEOCHRONOLOGY OR DETERMINATION OF ABSOLUTE AGES FOR GEOLOGIC EVENTS UNDERPINS MANY INQUIRIES INTO THE FORMATION AND EVOLUTION OF PLANETS AND OUR SOLAR SYSTEM. THE BOMBARDMENT CHRONOLOGY INFERRED FROM LUNAR SAMPLES HAS PLAYED A SIGNIFICANT ROLE IN THE DEVELOPMENT OF MODELS OF EARLY SOLAR SYSTEM AND EXTRASOLAR PLANET DYNAMICS AS WELL AS THE TIMING OF VOLATILE ORGANIC AND SIDEROPHILE ELEMENT DELIVERY. ABSOLUTE AGES OF ANCIENT AND RECENT MAGMATIC PRODUCTS PROVIDE STRONG CONSTRAINTS ON THE DYNAMICS OF MAGMA OCEANS AND CRUSTAL FORMATION AND THE LONGEVITY AND EVOLUTION OF INTERIOR HEAT ENGINES AND DISTINCT MANTLE/CRUSTAL SOURCE REGIONS. ABSOLUTE DATING ALSO RELATES HABITABILITY MARKERS TO THE TIMESCALE OF EVOLUTION OF LIFE ON EARTH. MAJOR ADVANCES IN PLANETARY SCIENCE CAN THUS BE DRIVEN BY ABSOLUTE GEOCHRONOLOGY IN THE NEXT DECADE CALIBRATING BODY-SPECIFIC CHRONOLOGIES AND CREATING A FRAMEWORK FOR UNDERSTANDING SOLAR SYSTEM FORMATION THE EFFECTS OF IMPACT BOMBARDMENT ON LIFE AND THE EVOLUTION OF PLANETS AND INTERIORS. ABSOLUTE AGES FOR MULTIPLE WORLDS ARE A DESIRE IN BOTH THE 2003 AND 2013 PLANETARY SCIENCE DECADAL SURVEYS BUT IN THESE TWO DECADES ONLY SAMPLE RETURN WAS CONSIDERED A VIABLE METHOD FOR GEO-CHRONOLOGY. THE DECADAL SURVEYS RECOMMENDED MISSION LISTS REFLECT THE REALITY FOR THOSE DECADES THAT SAMPLE RETURN IS THE ONLY WAY TO YIELD RELIABLE AND INTERPRETABLE GEOCHRONOLOGY. IN THE LAST TWO DECADES NASA HAS ALSO INVESTED IN THE DEVELOPMENT OF IN SITU DATING TECHNIQUES INCREASING THE TECHNOLOGY READINESS LEVELS OF INSTRUMENTS USING COMPLEMENTARY RADIOGENIC ISOTOPIC SYSTEMS (K-AR AND RB-SR) TO TRL 6. THE TIME IS RIGHT TO CONSIDER HOW THE PRECISION ACHIEVABLE WITH IN SITU GEOCHRONOLOGY CAN ADVANCE IMPORTANT SCIENCE GOALS FOR THE NEXT DECADAL SURVEY THE MOST FRUITFUL WAY TO DEPLOY THEM IN MISSIONS TO KEY PLANETARY DESTINATIONS AND TO CONSIDER HOW THESE TECHNOLOGIES COMPLEMENT SAMPLE-RETURN EFFORTS FOR THE MOON AND MARS. FOR THIS PLANETARY MISSION CONCEPT STUDY WE WILL FORMULATE AND COST A MEDIUM- OR FLAG-SHIP-CLASS MISSION FOR SOLAR SYSTEM CHRONOLOGY. THE AIM OF THIS PROPOSAL IS TO GIVE THE NEXT DECADAL SURVEY PANEL A VIABLE ALTERNATIVE OR ADDITION TO SAMPLE RETURN MISSIONS TO ACCOMPLISH LONGSTANDING GEOCHRONOLOGY GOALS WITHIN A NEW FRONTIERS ENVELOPE. OUR SCIENCE DEFINITION TEAM (SDT) HAS EXPERTISE ACROSS THE MOON MARS AND SMALL BODIES COMMUNITIES TO IDENTIFY THE MOST IMPORTANT SCIENCE QUESTIONS THAT CAN BE ANSWERED IN THE NEXT DECADE USING THE FIRST GENERATION OF IN SITU DATING TECHNIQUES AND EXAMINE MISSION-LEVEL REQUIREMENTS TRADES AND INSTRUMENTATION FOR ANSWERING THESE QUESTIONS. BY CONDUCTING THIS STUDY WE WILL PROVIDE THE NEXT DECADAL SURVEY PANEL WITH SEVERAL OPTIONS FOR HOW GEOCHRONOLOGY MIGHT BE ACCOMPLISHED IN THE INNER SOLAR SYSTEM WITHIN THE PLANETARY SCIENCE PORTFOLIO THE SYNERGIES THESE MEASUREMENTS HAVE WITH OTHER HIGH-PRIORITY SCIENCE GOALS AND THE TECHNOLOGY INVESTMENTS REQUIRED TO IMPLEMENT SUCH MISSIONS.