OUR UNDERSTANDING OF THE ORIGIN AND EARLY EVOLUTION OF PLANETARY ATMOSPHERE IS PRIMARILY BASED ON COMPARATIVE STUDIES OF NOBLE GAS ELEMENTAL AND ISOTOPIC COMPOSITIONS IN PLANETARY ATMOSPHERES AND KNOWN POTENTIAL PRECURSORS SUCH AS PRIMITIVE METEORITES COMETARY ICE AND THE SUN. COMETS ARE LEAST KNOWN OF THOSE. ROSETTA MISSION MADE A BREAKTHROUGH OF REPORTING ABUNDANCES AND ISOTOPIC COMPOSITIONS OF NOBLE GASES FROM 67P/CG FOR THE FIRST TIME IN HISTORY. THE RESULTS ARE IN SOME CASES INTERPRETED ASSUMING THAT THE MEASURED VALUES REPRESENT THAT OF NUCLEUS WHEREAS OTHERS CONSIDER CHEMICAL FRACTIONATION DURING PHASE CHANGES OF ICE ON HEATING. AS A POTENTIAL PRECURSOR OF PLANETARY BODIES IT IS HIGHLY DESIRABLE TO DETERMINE THE CHEMICAL COMPOSITION OF THE NUCLEUS. HOWEVER ROSINA SPACECRAFT'S MEASUREMENTS WERE ON THE COME THE GAS PHASE RELEASED FROM THE NUCLEUS IN RESPONSE TO AN EXTERNAL HEATING FROM THE SUN. IN ORDER TO LINK THE ROSINA MEASUREMENTS OF THE COMA AND THE CHEMICAL COMPOSITION BULK NUCLEUS IT IS ESSENTIAL TO DETERMINE THE DEGREE OF CHEMICAL FRACTIONATION THAT ACCOMPANIES THE STRUCTURAL CHANGE OF WATER ICE AND EVAPORATIVE GAS LOSS IN RESPONSE TO HEATING AND IRRADIATION. THE OBJECTIVE OF THE PROPOSED PROJECT IS TO QUANTITATIVELY UNDERSTAND THE DEGREE OF CHEMICAL FRACTIONATION AND INVENTORY OF MAJOR VOLATILES AND NOBLE GAS THAT WERE IN THE NUCLEUS 67P/CG. WE PLAN TO EXPERIMENTALLY SIMULATE THE FATE OF TRAPPED AND CONDENSED GASES IN OR ON WATER ICE BY PERFORMING CRYOGENIC STEPWISE-HEATING EXPERIMENTS UNDER CONTROLLED PRESSURE. GAS RELEASE AT THE SURFACE WOULD BE SIMULATED BY PUMPING THE ICE CELL DURING THE EXPERIMENTS WHEREAS SUBSURFACE PROCESS WOULD BE SIMULATED BY OPERATING THE CRYOGENIC STEPWISE-HEATING EXPERIMENTS IN THE PRESENCE OF GAS. WE AIM TO DETERMINE THE CHEMICAL COMPOSITION AND WATER ICE STRUCTURE OF 67P/CG'S NUCLEUS REQUIRED TO PRODUCE THE GAS COMPOSITION OBSERVED BY ROSINA. THE WORK PROPOSED HERE IS HIGHLY RELEVANT TO THE SCOPE OF NASA'S ROSETTA DATA ANALYSIS PROGRAM WHICH AIMS TO ENHANCE THE SCIENTIFIC RETURN OF THE ROSETTA MISSION. THE RESULTS OF THE PROPOSED STUDY ALSO HAVE DIRECT BEARING ON COSMOCHEMICAL/GEOCHEMICAL IMPLICATION OF 67P/CG'S GAS COMPOSITION REPORTED BY ROSETTA MISSION WHICH IS ALSO WITHIN THE SCOPE OF THIS PROGRAM.