DAILY AVERAGE ATMOSPHERIC PRESSURE ON MARS VARIES FROM LESS THAN 700 PA TO 1000 PA SEASONALLY ACCORDING TO THE DATA OBTAINED BY THE VIKING LANDERS AND THE ROVER ENVIRONMENTAL MONITORING STATION (REMS) OF THE CURIOSITY ROVER. MARS' ATMOSPHERIC PRESSURE ALSO VARIES DIURNALLY WITH A RANGE OF ~100 PA. REGOLITH ON MARS BREATHES IN SYNC WITH THE CHANGES IN ATMOSPHERIC PRESSURE AND THE PHENOMENON IS CALLED BAROMETRIC PUMPING. PREVIOUS LABORATORY MEASUREMENTS HAVE SHOWN THAT THERMAL CONDUCTIVITY OF PLANETARY REGOLITH SIMULANTS IS VERY SENSITIVE TO THE PORE GAS PRESSURE IN THE RANGE OBSERVED ON MARS. THE THERMAL CONDUCTIVITY MAY INCREASE BY 2 TO 3 TIMES FROM 600 PA TO 1000 PA. OTHER LAB EXPERIMENTS HAVE SHOWN THAT THERMAL CONDUCTIVITY OF THE SIMULANTS VARIES ALSO WITH TEMPERATURE. IN THE RANGE OF DIURNAL AND SEASONAL TEMPERATURE SWINGS EXPECTED AT THE INSIGHT LANDING SITE THERMAL CONDUCTIVITY OF THE SURFACE REGOLITH MAY FLUCTUATE BY MORE THAN 10% DUE TO THE EFFECT OF TEMPERATURE ALONE. THE INSIGHT MISSION PLANS TO DETERMINE THE ENDOGENIC HEAT FLOW OF THE LANDING SITE AS A PRODUCT OF TWO SEPARATE MEASUREMENTS OF THERMAL GRADIENT IN AND THERMAL CONDUCTIVITY OF THE REGOLITH PENETRATED BY THE HEAT FLOW AND PHYSICAL PROPERTIES PROBE (HP3). THE PROBE WILL MEASURE THERMAL CONDUCTIVITY WITH 50-CM DEPTH INTERVALS AS IT PENETRATES INTO THE REGOLITH. ONLY ONE MEASUREMENT WILL BE MADE AT EACH DEPTH. THE SENSITIVITY OF THE REGOLITH'S THERMAL CONDUCTIVITY TO PORE GAS PRESSURE AND TEMPERATURE IMPLIES THAT HP3 MAY BE ABLE TO CAPTURE ONLY A SNAPSHOT OF THE REGOLITH'S THERMAL CONDUCTIVITY AT EACH DEPTH AS IT FLUCTUATES SEASONALLY BY POSSIBLY MORE THAN 100%. THE OBJECTIVE OF THE RESEARCH PROPOSED HERE IS TO DETERMINE THE EFFECTIVE THERMAL CONDUCTIVITY OF THE REGOLITH THAT IS RELEVANT TO THE LONGTERM (DECADES OR LONGER) SURFACE HEAT EXCHANGE AT THE LANDING SITE. TO ACHIEVE THE OBJECTIVE WE PROPOSE TO CARRY OUT THE FOLLOWING THREE LINES OF WORK IN COLLABORATION WITH THE INSIGHT TEAM: (1) REPEAT IN-SITU THERMAL CONDUCTIVITY MEASUREMENTS AT THE BOTTOM OF THE HOLE USING HP3 IN A WIDE RANGE OF MARS' ATMOSPHERIC PRESSURES (MONITORED BY THE AUXILIARY PAYLOAD SENSOR SUITE). (2) CONDUCT THERMAL CONDUCTIVITY MEASUREMENTS ON TWO TYPES OF MARS REGOLITH SIMULANTS (MMS AND EIFELSAND) IN A VACUUM CHAMBER IN THE RANGE OF CO2 GAS PRESSURES AND TEMPERATURES OBSERVED AT THE LANDING SITE. IF THE INSIGHT TEAM DETERMINES THAT THE REGOLITH AT THE LANDING SITE IS NOT ADEQUATELY REPRESENTED BY THESE SIMULANTS A NEW SIMULANT MAY BE DEVELOPED AND TESTED. (3) BY SYNTHESIZING THE DATA FROM (1) AND (2) DEVELOP A MATHEMATICAL MODEL FOR THE PRESSURE AND TEMPERATURE EFFECTS ON THE REGOLITH'S THERMAL CONDUCTIVITY. THAT WILL BE INCORPORATED INTO A THERMAL MODEL FOR THE HEAT EXCHANGE AT MARS' SURFACE AND SHALLOW SUBSURFACE WHICH YIELDS THE EFFECTIVE LONG-TERM THERMAL CONDUCTIVITY OF THE REGOLITH OF THE LANDING SITE.