NASA'S NEW HORIZONS MISSION HAS RECENTLY REVEALED THE COMPLEX CRYOGENIC WORLD OF PLUTO (STERN ET AL. 2015). THE STRIKING SPATIAL HETEROGENEITY OF THIS LARGE TRANS-NEPTUNIAN OBJECT RESULTS FROM A VARIETY OF PROCESSES INCLUDING THE SEASONAL TRANSPORT OF NITROGEN (N2) METHANE (CH4) AND CARBON MONOXIDE (CO) ICES. ALL THREE ICES ARE INDEED MOBILE AT PLUTO'S SURFACE TEMPERATURE OF ~40 K WITH CO AND N2 BEING MUCH MORE VOLATILE THAN CH4. OVER SEASONAL TIMESCALES VARYING PATTERNS OF INSOLATION ARE THOUGHT TO CAUSE SUBLIMATION AND REDISTRIBUTION OF THESE VOLATILE ICES. WHILE NEW HORIZONS HAS RETURNED A DETAILED UP-CLOSE SNAPSHOT OF PLUTO IN 2015 A BROAD SEASONAL CONTEXT IS NEEDED TO IMPROVE OUR UNDERSTANDING OF THE PROCESSES RESPONSIBLE FOR PLUTO'S EVOLUTION. THIS CAN ONLY BE ACHIEVED THROUGH ANALYSIS OF DATA THAT MONITOR PLUTO OVER TIMESCALES OF YEARS. BY ANALYZING OVER A DECADE'S-WORTH OF IRTF/SPEX SPECTRA WITHIN A MODERN RADIATIVE TRANSFER CODE WE WILL SYSTEMATICALLY AND QUANTITATIVELY INVESTIGATE THE SPATIAL DISTRIBUTION AND LONG TERM EVOLUTION OF PLUTO'S VOLATILE ICES WHILE IDENTIFYING THE PHYSICAL AND CHEMICAL PROCESSES THAT GOVERN THE INTERACTIONS BETWEEN PLUTO'S SURFACE AND ITS ATMOSPHERE. THE PROPOSED INVESTIGATION IS A QUANTITATIVE EXTENSION OF THE QUALITATIVE ANALYSIS THAT HAS BEEN DONE ON THE IRTF DATA SO FAR (GRUNDY ET AL. 2013 2014). ACCORDING TO THEIR ANALYSIS THE SPATIAL AND TEMPORAL PATTERNS OF CH4 ARE DIFFERENT THAN THAT OF N2 AND CO ICES. GRUNDY ET AL. (2013 2014) PUT FORTH THE IDEA OF A POSSIBLE GROWTH AND/OR NUCLEATION OF SMALL CH4-RICH CRYSTALS OVER TIME. HOWEVER THIS SPECULATION CAN BE CONFIRMED OR DISPROVED ONLY THROUGH A QUANTITATIVE MODELING IN COMPLIANCE WITH THERMODYNAMIC EQUILIBRIUM CONSIDERATIONS WHICH IS WHAT WE PROPOSE HERE. THIS MODELING TAKES INTO ACCOUNT THE PHASE STABILITY IN A CH4-N2 BINARY SYSTEM USING THE LATEST OPTICAL CONSTANTS BY PROTOPAPA ET AL. (2015) AND THE RECENT FINDINGS FROM NEW HORIZONS (E.G. PROTOPAPA ET AL. 2017).