OVERVIEW: HUNDREDS OF MILLIONS OF DOLLARS ARE BEING INVESTED IN TECHNOLOGY TO DIRECTLY DETECT M-DWARF PLANETS AND SEARCH FOR SIGNS OF LIFE. HOWEVER THE INTERACTION BETWEEN THE UNIQUE SPECTRAL ENERGY DISTRIBUTIONS (SEDS) OF M-DWARF STARS AND THEIR PLANETS' COMPLEX ATMOSPHERES AND SURFACES DEFY SIMPLE MODELING PRESCRIPTIONS. ONE OF THESE POSSIBLE SURFACE TYPES IS SODIUM CHLORIDE DIHYDRATE OR HYDROHALITE (NACL 2H2O) WHICH COULD FORM ON COLD DRY M-DWARF PLANETS AS A RESULT OF SALT WITHIN BRINE INCLUSIONS IN BARE SEA ICE PRECIPITATING IN CRYSTAL FORM AT LOW-ENOUGH TEMPERATURES. EXPOSED LAND SURFACES MAY ALSO BE WIDESPREAD GIVEN THE LOW POTENTIAL WATER INVENTORY ON M-DWARF PLANETS. THE IMPACT OF THESE SURFACE ALBEDO FEEDBACK MECHANISMS ON THE CLIMATE OF M-DWARF PLANETS HAS NOT BEEN EXPLORED AND MUST BE QUANTIFIED TO INFORM OBSERVATIONAL INTERPRETATION. I PROPOSE TO CALCULATE THE EFFECTS ON M-DWARF PLANET HABITABILITY OF HYDROHALITE AND LAND SURFACES USING SOPHISTICATED 3D GLOBAL CLIMATE MODELS. I WILL ALSO PRODUCE A REALISTIC ASSESSMENT OF THE HABITABILITY AS A FUNCTION OF THESE POSSIBLE SURFACE TYPES OF TWO OF THE MOST SCIENTIFICALLY INTERESTING M-DWARF PLANETS DISCOVERED TO DATE GIVEN A RANGE OF PLAUSIBLE ATMOSPHERIC COMPOSITIONS AND ROTATION RATES FOR THESE PLANETS. SPECIFIC SCIENCE OBJECTIVES: THIS PROPOSAL ADDRESSES THE EFFECTS ON HABITABILITY OF DIFFERENT SURFACE ALBEDO FEEDBACK PROCESSES THAT MAY BE POSSIBLE ON M-DWARF PLANETS. IN THE COURSE OF THIS WORK WE WILL: (1) QUANTIFY THE EFFECTS ON PLANETARY CLIMATE AND HABITABILITY OF THE INTERACTION BETWEEN THE M-DWARF SED AND HYDROHALITE AND LAND SURFACES ON ORBITING PLANETS AS COMPARED WITH OCEAN- ICE- AND SNOW-COVERED SURFACES. (2) DETERMINE THE EFFECT OF DIFFERENT ATMOSPHERIC COMPOSITIONS AND PLANETARY SPIN STATES ON A PLANET S CLIMATE SENSITIVITY TO THESE SURFACE FEEDBACK PROCESSES. (3) SIMULATE THE CLIMATES OF M-DWARF PLANETS KEPLER-186F AND PROXIMA CENTAURI B TO EXPLORE AND QUANTIFY THE HABITABILITY OF THESE SYSTEMS AS A FUNCTION OF THIS SUITE OF SURFACE TYPES. PROPOSED METHODOLOGY: TO MEET OUR GOALS WE WILL USE ALBEDO SPECTRA FOR PURE WATER ICE AND SNOW (WITHOUT SALTS) HYDROHALITE AND LAND AS INPUT TO CLIMATE SIMULATIONS OF EARTH-SIZED PLANETS ORBITING M-DWARF HOST STARS USING 3D GLOBAL CLIMATE MODELS ADAPTED BY THE PI TO SIMULATE THE CLIMATE OF PLANETS ORBITING STARS OF DIFFERENT SPECTRAL TYPES. WE WILL EXPLORE A RANGE OF ATMOSPHERIC COMPOSITIONS AND PLANETARY SPIN STATES IN THESE SIMULATIONS TO IDENTIFY ATMOSPHERIC LEVELS THAT MAY MASK THESE SURFACE ALBEDO FEEDBACK PROCESSES AND QUANTIFY THE EFFECT OF ROTATION RATE ON A PLANET S CLIMATE SENSITIVITY TO THESE SURFACE INTERACTIONS. NEXT WE WILL APPLY THESE RESULTS TO SIMULATIONS OF THE CLIMATES OF KEPLER-186F AND PROXIMA CENTAURI B TWO RECENTLY DISCOVERED POTENTIALLY HABITABLE M-DWARF PLANETS. RELEVANCE: THIS PROPOSAL EXPLORES THE SURFACE TYPES POSSIBLE ON EXOPLANETS AND THEIR RADIATIVE EFFECTS ON THE HABITABILITY OF M-DWARF PLANETS IN PARTICULAR. THEREFORE IT IS DIRECTLY RELEVANT TO THE HABITABLE WORLDS CALL. OUR WORK WILL ADD MUCH-NEEDED COMPLEXITY TO THEORETICAL SIMULATIONS AND HAS DIRECT IMPLICATIONS FOR EXPERIMENTAL DESIGN. THESE RESULTS WILL BE CRITICAL TO PROVIDING AN ACCURATE ASSESSMENT OF THE POTENTIAL HABITABILITY OF EXOPLANETS AS THEY ARE DISCOVERED AND CHARACTERIZED BY MISSIONS SUCH AS NASA S TRANSITING EXOPLANET SURVEY SATELLITE AND NASA S JAMES WEBB SPACE TELESCOPE RESPECTIVELY AS WELL AS THE NEXT GENERATION OF SPACE-BASED MISSIONS.