MOTIVATION: MOST PLANETARY SYSTEMS INCLUDING OUR SOLAR SYSTEM FORMED IN STELLAR CLUSTERS CENTERED ON MASSIVE O/B-TYPE STARS. IN SUCH CLUSTERS ULTRAVIOLET (UV) RADIATION EMITTED BY HIGH-MASS STARS PHOTO-EVAPORATES PROTOPLANETARY DISKS HOSTED BY LOWER-MASS STARS LIKE THE SUN. THIS PROCESS OF EXTERNAL PHOTO-EVAPORATION WORKS BY HEATING CIRCUMSTELLAR GAS TO ESCAPE VELOCITY. BLOWING OFF THE GAS ALSO REDUCES THE DUST CONTENT OF DISKS IN TWO WAYS: EITHER BY ENTRAINING DUST IN THE GAS OUTFLOW DIRECTLY OR BY WEAKENING DUST-GAS COUPLING TO ENABLE SOLIDS TO UNDERGO FASTER ORBITAL DECAY ONTO THE HOST STAR. THE UV ENVIRONMENTS IN OB CLUSTERS ALSO BETTER IONIZE DISKS WHICH MAY INDIRECTLY ACCELERATE GAS DISK DISPERSAL VIA MAGNETICALLY DRIVEN WINDS OR DISK TURBULENCE. ADDITIONALLY SUPERNOVAE IN MASSIVE STAR CLUSTERS SEED DISKS WITH RADIOACTIVE ELEMENTS THAT ARE CRITICAL FOR THE HEATING OF PLANETARY INTERIORS. FOR ALL THESE REASONS PLANETARY SYSTEMS BORN IN THE VICINITY OF MASSIVE STARS LIKELY LOOK DIFFERENT FROM THOSE BORN FARTHER AWAY. METHODOLOGY: EMISSION AT SUB-MM TO MM WAVELENGTHS PROBES THE OUTER REGIONS OF CIRCUMSTELLAR DISKS WHICH ARE MOST PRONE TO UV PHOTO-EVAPORATION. CONTINUUM AND CO LINE OBSERVATIONS AT THESE WAVELENGTHS PROVIDE FUNDAMENTAL MEASUREMENTS OF DISK MASSES AND SIZES BOTH IN DUST AND IN GAS WHICH ARE KEY DIAGNOSTICS OF THE IMPACTS OF EXTERNAL PHOTO-EVAPORATION. TO STUDY THE EFFECTS OF CLUSTERED ENVIRONMENTS ON DISK EVOLUTION WE ARE CONDUCTING COMPLETE SURVEYS OF PROTOPLANETARY DISK POPULATIONS IN OB CLUSTERS USING THE ATACAMA LARGE MILLIMETER ARRAY (ALMA); CONTINUUM AND LINE DATA HAVE BEEN OBTAINED OR ARE IN THE QUEUE FOR A-RANKED (I.E. GUARANTEED OBSERVATION) PROGRAMS. OUR SURVEYED REGIONS SPAN A CRITICAL RANGE OF AGES FROM ~1 MYR (ORION + NGC 2024) TO ~3 MYR (SIGMA ORIONIS) TO ~5 MYR (LAMBDA ORIONIS) ALLOWING US TO PROBE HOW THE IONIZING EFFECTS ON DISKS ACCUMULATE WITH TIME AND EVEN ACCELERATE AS INTRA-CLUSTER CLOUD MATERIAL DISPERSES (VIA E.G. A SUPERNOVA AS MAY HAVE OCCURRED IN LAMBDA ORIONIS). OUR PROPOSED REDUCTION AND ANALYSIS OF THESE MM-WAVE DATASETS WILL BE COMPLEMENTED BY A FULL SUITE OF RADIATIVE-HYDRODYNAMIC SIMULATIONS OF PHOTO-EVAPORATING DISKS ENABLING INFERENCES OF MASS LOSS RATES AS FUNCTIONS OF UV ENVIRONMENT STELLAR MASS DISK MASS AND DISK RADIUS. THESE SAME DISK MODELS CAN BE USED TO CALCULATE AERODYNAMIC DRIFT RATES OF SOLID PARTICLES AND THE DEGREE TO WHICH DUST IS DRAINED FROM THE OUTSIDE IN WHICH WILL BE KEY TO INTERPRETING OUR MM CONTINUUM OBSERVATIONS. ADDITIONALLY WE WILL OBTAIN VLT/ X-SHOOTER SPECTRA WHICH UNIQUELY COVER UV TO OPTICAL WAVELENGTHS AT HIGH SENSITIVITY AND MODERATE SPECTRAL RESOLUTION TO CONFIRM ENHANCED LEVELS OF DISK IONIZATION (VIA FORBIDDEN LINE DIAGNOSTICS) AND INCREASED STELLAR MASS ACCRETION RATES AS EXPECTED IN ELEVATED UV ENVIRONMENTS. IMPACT/RELEVANCE: ALTHOUGH MANY STUDIES OF SOLAR SYSTEM FORMATION ASSUME FOR SIMPLICITY THAT THE PROTO-SOLAR NEBULA EVOLVED IN ISOLATION THE METEORITIC RECORD THE DEMOGRAPHICS OF STAR-FORMING REGIONS AND THE DYNAMICALLY EXCITED STATE OF THE KUIPER BELT/ INNER OORT CLOUD ALL POINT CLEARLY TO PLANET FORMATION WITHIN A CLUSTER CONTAINING SEVERAL THOUSAND STARS OF WHICH THE MOST MASSIVE MEMBERS WILL BE PRODIGIOUS EMITTERS OF UV LIGHT. MEASURING THE GAS AND DUST MASS DISTRIBUTIONS OF PROTOPLANETARY DISKS WITHIN SUCH ORION-LIKE ENVIRONMENTS ALIGNS DIRECTLY WITH THE EMERGING WORLDS MISSION TO "STUDY ALL ASPECTS OF MATERIALS AND PROCESSES ... IN THE PROTOPLANETARY DISK." SUCH PROCESSES AS WE WILL STUDY INCLUDE UV-POWERED PHOTO-EVAPORATIVE WINDS; MAGNETICALLY DRIVEN DISK ACCRETION ENABLED BY UV IONIZATION; AND THE TRANSPORT AND DISTRIBUTION OF SOLIDS THE RAW MATERIALS FROM WHICH PLANETARY CORES ARE BUILT.