THE ATMOSPHERES OF PLUTO, TRITON AND TITAN ARE COLD AND HAZY, PROVIDING A UNIQUE OPPORTUNITY TO STUDY HOW HAZE PARTICLES INFLUENCE THE ATMOSPHERIC THERMAL STRUCTURES ON THOSE LOW-GRAVITY ICY BODIES. THEIR TEMPERATURE AND HAZE PARTICLE DISTRIBUTIONS HAVE BEEN DERIVED FROM BOTH GROUND-BASED STELLAR OCCULTATION AND SPACECRAFT FLYBY MEASUREMENTS FROM VOYAGER, CASSINI AND NEW HORIZONS. RECENTLY OUR TEAM HAS DISCOVERED THAT HYDROCARBON HAZE PARTICLES COULD CONTROL THE RADIATIVE HEATING AND COOLING OF PLUTO'S ATMOSPHERE. IT IMPLIES THAT HAZE PARTICLES MIGHT ALSO HAVE SUBSTANTIAL RADIATIVE EFFECTS ON THE TEMPERATURE STRUCTURES ON TRITON AND THE UPPER ATMOSPHERE OF TITAN (400-1000 KM) BUT THE EFFECTS HAVE NOT BEEN THOROUGHLY INVESTIGATED. HERE WE PROPOSE A SYSTEMATIC STUDY ON ALL THREE ICY BODIES. FOR EACH BODY, WE PLAN TO USE A WELL-ESTABLISHED MICROPHYSICAL MODEL OF HYDROCARBON HAZE FORMATION TO PREDICT THE DISTRIBUTIONS OF PARTICLE SIZE AND ABUNDANCE. THEN WE WILL USE A THERMAL STRUCTURE MODEL WITH THE RADIATIVE EFFECTS FROM HAZES AND GASES TO INVESTIGATE THE HAZE RADIATIVE EFFECT ON THE THERMAL STRUCTURE OF THE ATMOSPHERE. OBSERVED PARTICLE OPACITIES AND REFLECTION SPECTRA WILL BE USED TO CONSTRAIN THE HAZE FORMATION MODEL AND THE RESULTANT THERMAL STRUCTURES WILL BE COMPARED WITH THE OBSERVATIONS. WE WILL ALSO PRODUCE THERMAL ROTATIONAL LIGHT CURVES AND INFRARED SPECTRA TO COMPARE WITH AVAILABLE SPITZER OBSERVATIONS AND THE PLANNED JAMES WEBB SPACE TELESCOPE GTO OBSERVATIONS ON PLUTO AND TRITON DURING THIS PROPOSAL PERIOD. BASED ON THE INDIVIDUAL INVESTIGATION OF EACH BODY AND COMPARATIVE PLANETOLOGY, WE WILL UNVEIL THE UNDERLYING PHYSICAL MECHANISM THAT GOVERNS THE ENERGY BALANCE ON THOSE COLD AND HAZY ATMOSPHERES. THIS PROPOSAL CLEARLY FITS THE OBJECTIVES OF THE NASA SOLAR SYSTEM WORKING PROGRAM AND MEETS THE FOLLOWING SOLICITATION OBJECTIVES: "RESEARCH RELATED TO UNDERSTANDING THE ATMOSPHERIC, CLIMATOLOGICAL, DYNAMICAL, ..., PROCESSES OCCURRING WITHIN THE SOLAR SYSTEM".