Constraints on the formation and diagenetic history of Gale crater strata from physical properties

THE BULK PHYSICAL PROPERTIES (GRAIN SIZE POROSITY DENSITY) OF ROCKS ARE STRONGLY INFLUENCED BY DEPOSITIONAL PROCESS BURIAL DEPTH AND ALTERATION. THEREFORE CONSTRAINTS ON PHYSICAL PROPERTIES ARE IMPORTANT FOR INTERPRETING THE DEPOSITIONAL AND DIAGENETIC HISTORY OF STRATA WITHIN THE FLOOR AND CENTRAL MOUND OF GALE CRATER. THE FORMATION AND DIAGENETIC HISTORY OF STRATA IN TURN ARE KEY TO ASSESSING THE DURATION AND CHARACTERISTICS OF HABITABLE CONDITIONS AND THE FATE OF ANY BIOGENIC MOLECULES THAT MAY HAVE FORMED. THE OBJECTIVE OF THE PROPOSED INVESTIGATION IS TO ESTIMATE BULK DENSITY AND POROSITY OF OUTCROPS TRAVERSED BY THE CURIOSITY ROVER FROM REMS GROUND TEMPERATURE SENSOR (GTS)-DERIVED THERMAL INERTIA AND USE THIS INFORMATION TO HELP EVALUATE HYPOTHESES FOR THE DEPOSITIONAL AND DIAGENETIC HISTORY OF STRATA IN AEOLIS MONS. FIRST A THERMAL MODEL WILL BE USED TO DERIVE THERMAL INERTIA VALUES FOR OUTCROPS FROM GTS DIURNAL SURFACE TEMPERATURE MEASUREMENTS. IMAGE-BASED ESTIMATES OF SEDIMENT COVER WILL HELP TO FURTHER REFINE THE MODELS. NEXT OUTCROP THERMAL INERTIA VALUES WILL BE COMPARED WITH LABORATORY THERMAL INERTIA MEASUREMENTS OF ROCKS OF KNOWN BULK DENSITY POROSITY AND COMPOSITION PERMITTING ESTIMATES OF OUTCROP BULK DENSITY AND POROSITY. THESE VALUES WILL THEN BE USED TO EVALUATE HYPOTHESES FOR DEPOSITION AND DIAGENESIS WITH A MAJOR FOCUS ON THE MG-SULFATE UNITS. FOR EXAMPLE IF SULFATES OCCUR AS POREFILLING CEMENTING MATERIALS INDICATIVE OF AUTHIGENESIS AND INTERACTION WITH FLUIDS IN GALE CRATER A LOW POROSITY AND HIGHER BULK DENSITY WOULD BE EXPECTED CONSISTENT WITH WELL-CEMENTED SANDSTONES ON EARTH. POROSITY AND BULK DENSITY WOULD ALSO BE EXPECTED TO VARY WITH SULFATE CONCENTRATION. IF THE SULFATES INSTEAD MANIFEST AS LOCALLY RE-WORKED AIRFALL OR TRANSPORTED MATERIALS A HIGHER POROSITY CONSISTENT WITH TERRESTRIAL LOESS OR WEAKLY-CEMENTED MUDSTONES OR SANDSTONES WOULD BE EXPECTED WITH NO CORRELATION BETWEEN POROSITY AND SULFATE ABUNDANCE. FOR SELECT TARGETS SAMPLED BY CHEMIN LABORATORY THERMAL INERTIA MEASUREMENTS OF SIMULATED TARGETS WILL BE ACQUIRED CREATED BY SYNTHESIZING MINERAL AND AMORPHOUS MIXTURES AND COMPACTING THEM UNDER VARYING PRESSURES. THIS DATASET WILL PROVIDE A DIRECT COMPARISON TO THE GTS-DERIVED THERMAL INERTIA VALUES FOR ADDITIONAL CONSTRAINTS ON POROSITY AND BULK DENSITY. THE PROPOSED INVESTIGATION PROVIDES COMPLEMENTARY PHYSICAL PROPERTY INFORMATION TO THAT DERIVED FROM THE POWDER ACQUISITION DRILL SYSTEM (PADS) AND ROVER ACCELEROMETER DATA BECAUSE TI-BASED ESTIMATES FALL AT AN INTERMEDIATE SPATIAL SCALE AND DEPTH SENSITIVITY BETWEEN THESE TWO METHODS. THE INVESTIGATION WILL AID IN CHARACTERIZING THE GEOLOGICAL FEATURES CONTRIBUTING TO DECIPHERING GEOLOGICAL HISTORY AND THE PROCESSES THAT HAVE FORMED OR MODIFIED BEDROCK AND REGOLITH WITH EMPHASIS ON THE ROLE OF WATER (MSL SCIENCE OBJECTIVE) AND THEREFORE IS RELEVANT TO THIS CALL FOR PROPOSALS. HOURLY GTS OBSERVATIONS ARE SYSTEMATICALLY ACQUIRED BY CURIOSITY HOWEVER OUR PARTICIPATION IN DAILY AND LONG-TERM PLANNING WILL ENSURE THAT OPTIMAL OBSERVATIONS NEEDED FOR THE ROBUST ROCK TI ESTIMATES ARE ACHIEVED.