AFTER MORE THAN 2 YEARS OF OPERATIONS IN THE VICINITY OF COMET 67P/CHURYUMOV-GERASIMENKO ESA S HIGHLY SUCCESSFUL EXPLORATORY SPACE MISSION ROSETTA CAME TO ITS CONCLUSION IN SEPTEMBER 2016. ROSETTA CARRIED ONBOARD A COMPREHENSIVE SUITE OF FIVE PLASMA INSTRUMENTS DESIGNED TO OBSERVE THE FORMATION AND EVOLUTION OF THE VARIOUS PLASMA INTERACTION REGIONS AS THE COMET TRAVELED ALONG ITS ELLIPTICAL ORBIT [CARR ET AL. SPACE SCI. REV. (2007)]. WHILE SOME OBSERVATIONS WERE EXPECTED MANY OTHERS WERE A COMPLETE SURPRISE AND HAVE RAISED MORE QUESTIONS THAN THEY HAVE BROUGHT ANSWERS. IN PARTICULAR THE ROLE OF THE DIFFERENT ELECTRON POPULATIONS OF THE NEARCOMET ENVIRONMENT [ERIKSSON ET AL. ASTRON.&ASTROPH. (2017)] IN THE VARIOUS OBSERVED INSTABILITIES AND WAVES IS POORLY UNDERSTOOD. A COMETARY IONOSPHERE IS FORMED WHEN THE OUTGASSING NEUTRAL ATMOSPHERE BECOMES IONIZED THROUGH PHOTOIONIZATION CHARGE EXCHANGE WITH SOLAR WIND IONS AND IMPACT IONIZATION OF HIGH-ENERGY ELECTRONS [CRAVENS ET AL. J. GEOPHYS. RES. (1987); GALAND ET AL. MON. NOT. R. ASTRON. SOC. (2016)]. THROUGH MASS-LOADING OF THE SOLAR WIND [BIERMANN ET AL. SOLAR PHYS. (1967); SZEGO ET AL. SPACE SCI. REV. (2000)] AND A NONCONSTANT COLLISION CROSS-SECTION FROM THE COMET [CRAVENS ET AL. ADV. SPACE RES. (1989)] VARIOUS PLASMA INTERACTION BOUNDARIES DEVELOP EVOLVE AND HAVE BEEN OBSERVED BY THE ROSETTA SPACECRAFT IN THE COMETARY PLASMA ENVIRONMENT [MANDT ET AL. MON. NOT. R. ASTRON. SOC. (2016)]. OUR GOAL IS TWOFOLD. (1) TO CHARACTERIZE THE STABILITY OF A WEAK COMETARY IONOSPHERE AS THE PLASMA TRANSITIONS FROM A COLLISIONAL TO A COLLISIONLESS INTERACTION REGION [VIGREN&ERIKSSON ASTRONOM. J. (2017)]. INSIDE THE ELECTRON COLLISIONOPAUSE A PART OF THE ELECTRON POPULATION IS COOLED BY COLLISIONS WITH THE NEUTRAL GAS WHEREAS THE WARM POPULATION IS CONSTITUTED OF LOCALLY-PRODUCED ELECTRONS RELEASED IN THE IONIZATION PROCESS THAT HAVE RETAINED THEIR ENERGY [GILET ET AL. RADIO SCI. (2017)]. STRONG DENSITY GRADIENTS HAVE BEEN OBSERVED AT THE BOUNDARY BETWEEN THESE TWO ELECTRON REGIMES [HENRI ET AL. MON. NOT. R. ASTRON. SOC. (2017)] PROVIDING A SOURCE OF FREE ENERGY FOR INSTABILITIES TO DEVELOP [KARLSSON ET AL. GEOPHYS. RES. LETT. (2017)]. (2) TO ASSESS THE PHYSICAL PROCESSES THAT CAUSE THE GENERATION OF THE ANOMALOUSLY LARGE DENSITY OF ENERGETIC ELECTRONS CLOSE TO THE COMET. THE LATTER HAVE BEEN OBSERVED NEXT TO THE COLD AND WARM POPULATIONS WITH ENERGIES RANGING FROM 15 UP TO 200 EV [CLARK ET AL. ASTRON.&ASTROPH. (2015)] HIGH ENOUGH TO IONIZE THE COMETARY NEUTRALS AND SERVE AS A SIGNIFICANT SOURCE POPULATION FOR THE COMETARY IONOSPHERE [HERITIER ET AL. ASTRON.&ASTROPH. (2018)]. IN THE LITERATURE THEIR PRESENCE HAS BEEN EXPLAINED BY HEATING THROUGH WAVEPARTICLE INTERACTIONS [BROILES ET AL MON. NOT. R. ASTRON. SOC. (2016)] OR THROUGH THE ACCELERATION OF SOLAR WIND ELECTRONS BY A COMETARY AMBIPOLAR ELECTRIC FIELD [MADANIAN ET AL J. GEOPHYS. RES. (2016)]. ONLY A 3D FULLY KINETIC MODEL THAT INCLUDES BOTH ELECTRON AND ION COLLISIONS CAN ASSESS THE UNDERLYING PHYSICAL PROCESSES THAT DOMINATE THE COMET-PLASMA INTERACTION [DECA ET AL. PHYS. REV. LETT. (2017)]. THE KEY QUESTION WE FOCUS ON IS HOW THE OBSERVED WAVES COUPLE TO THE UNDERLYING PARTICLE DISTRIBUTIONS AND THE OVERALL (GLOBAL) PLASMA STRUCTURE OF A WEAKLY OUTGASSING COMET. THIS STUDY WILL BRING CLARITY TO DISENTANGLE THE RELATIVE CONTRIBUTIONS OF THE VARIOUS PHYSICAL PROCESSES DEDUCED FROM THE MEASUREMENTS. BEING ABLE TO COMBINE THE FINDINGS OF A SUITE OF PLASMA OBSERVATIONS WITH A COMPREHENSIVE SELF-CONSISTENT 3D MODEL HELPS TO BETTER PREDICT THE PLASMA STRUCTURE AROUND OTHER COMETS WHICH ON ITS TURN ALLOWS DEFINING MORE ACCURATELY THE PERSPECTIVES FOR FUTURE COMETARY MISSIONS AND THE BEHAVIOR OF MASS-LOADING PLASMA IN SPACE.