CAESAR PHASE A. THE NEW FRONTIERS COMET ASTROBIOLOGY EXPLORATION SAMPLE RETURN (CAESAR) MISSION WILL ACQUIRE AND RETURN TO EARTH A MACROSCOPIC SAMPLE FROM THE SURFACE OF A COMET NUCLEUS AND DETERMINE THE GEOLOGIC AND GEOMORPHOLOGIC CONTEXT OF THE SAMPLE REGION. CAESAR'S SAMPLE ANALYSIS OBJECTIVES ADDRESS PLANETARY DECADAL SURVEY QUESTIONS THAT SEEK TO UNDERSTAND THE NATURE OF SOLAR SYSTEM STARTING MATERIALS AND HOW THESE PRIMITIVE COMPONENTS CAME TOGETHER TO FORM PLANETS AND GIVE RISE TO LIFE. USING ESTABLISHED EXPERTISE AND LABORATORY INSTRUMENTS, CAESAR WILL DETERMINE THE NATURE AND ABUNDANCES OF INTERSTELLAR GRAINS AND MOLECULAR CLOUD MATERIAL, AND DETERMINE THE ORIGINS AND AGES OF REFRACTORY SOLAR NEBULA CONDENSATES. IT WILL TRACE THE ORIGINS OF VOLATILE RESERVOIRS, DELINEATE THE CHEMICAL PATHWAYS THAT LED FROM SIMPLE INTERSTELLAR SPECIES TO COMPLEX AND PREBIOTIC MOLECULES, AND CONSTRAIN THE GEOLOGICAL AND DYNAMIC EVOLUTION OF THE COMET. AND IT WILL EVALUATE THE POTENTIAL ROLE OF COMETS IN DELIVERING WATER AND ORGANICS TO THE EARLY EARTH.