THE HABITABILITY OF EARLY MARS AND PERHAPS CURRENT MARS IS DIRECTLY TIED TO ITS EARLY CLIMATE. WAS EARLY MARS WARM AND WET OR COLD AND DRY? NUMEROUS THEORIES HAVE BEEN PROPOSED TO WARM MARS USING CO2 CO2+CH4 CO2+ SO2 BUT EACH OF THESE FAILS EVEN TO BRING MARS NEAR THE FREEZING POINT. SEVERAL BARS OF CO2 PLUS H2 MAY WORK BUT EVIDENCE SUGGESTS SUCH HIGH LEVELS OF CO2 DID NOT OCCUR AND AN ATMOSPHERE OF CO2 + H2 REQUIRES COMPLEX GEOCHEMISTRY SINCE ONE IS OXIDIZED AND ONE REDUCED. OUR GOAL IS TO BETTER UNDERSTAND THE CLOUDY GREENHOUSE SOLUTION OF THE FAINT YOUNG SUN PROBLEM FOR NOACHIAN MARS. URATA AND TOON (2013A B) SHOW STABLE CLIMATE STATES WITH GLOBAL AVERAGE TEMPERATURES NEAR THE FREEZING POINT AS WELL AS SUBSTANTIAL TROPICAL PRECIPITATION RATES CAN BE MAINTAINED ON ANCIENT MARS BY WATER CLOUDS ASSUMING THAT CARBON DIOXIDE LEVELS EXCEED A FEW HUNDRED MBARS. UNLIKE PREVIOUS PROPOSED SOLUTIONS CARBON DIOXIDE IS NOT A MAJOR GREENHOUSE GAS IN THIS MODEL BUT RATHER IS IMPORTANT FOR CARRYING HEAT TO THE POLE.WATER ICE CLOUDS PROVIDE THE GREENHOUSE WARMING. WE ARE NOW ABLE TO PREDICT WHERE RAIN FELL AND RUNOFF AMOUNTS WHICH ALLOWS US TO LINK CLIMATE MODELS DIRECTLY TO THE GEOLOGIC RECORD. THIS WORK MAY RESOLVE THE LONGSTANDING DEBATE ABOUT HOW MARTIAN RIVER VALLEYS FORMED AND WHETHER LAKES AND SEAS WERE STABLE AS LIQUIDS OR ONLY SHORT-LIVED BEFORE FREEZING. UNLIKE ALL OTHER SOLUTIONS TO THE EARLY MARS CLIMATE PROBLEM WE ONLY REQUIRE MODEST AMOUNTS OF CARBON DIOXIDE AND WE KNOW THE GREENHOUSE GASES CO2 AND H2O ARE PRESENT AND DO NOT INVOKE GASES FOR WHICH WE DO NOT HAVE OBSERVATIONAL EVIDENCE.IT IS SURPRISING THAT CLOUDS CAN CAUSE PLANETARY WARMING SINCE CLOUDS COOL EARTH. HOWEVER WE HAVE ALSO FOUND THAT ON ARCHEAN EARTH CLOUDS MAY HAVE PROVIDED WARMING. WE SEEK TO UNDERSTAND THESE TWO RADIATIVE BEHAVIORS OF CLOUDS WHICH WE BELIEVE REPRESENT NEW FUNDAMENTAL PLANETARY PHYSICS WITH IMPLICATIONS FOR OTHER PLANETS. THE MARS MODELING GROUP AT NASA AMES FINDS SIMILAR SOLUTIONS TO OURS BUT OTHERS HAVE NOT DUPLICATED OUR RESULTS. WE PLAN TO USE A MORE SOPHISTICATED AEROSOL AND CLOUD MODEL THAN WE USED IN THE PAST TO ELIMINATE SOME ASSUMPTIONS AND CLARIFY THE REQUIREMENTS TO OBTAIN THESE WARM CLIMATE SOLUTIONS. WE ALSO PLAN TO ADDRESS SUCH QUESTIONS ABOUT ANCIENT MARS AS WHETHER OCEANS WOULD FREEZE OVER WHETHER A STRONG HYDROLOGICAL CYCLE REQUIRES ONLY POLAR ICE DEPOSITS OR ALSO MIDLATITUDE ONES AND WHETHER IMPACTS ARE NEEDED TO INITIATE LONG-LASTING WARM CLIMATES CAUSED BY CLOUDS OR INSTEAD HIGH OBLIQUITY STATES WILL WORK. WE WILL ALSO EXPLORE SEVERAL ISSUES RELATED TO MODERN MARS INCLUDING THE PHYSICS OF HIGH ALTITUDE CLOUDS AND THE INTERACTION OF NIGHTTIME FROST WITH THE SOIL WHICH MAY LEAD TO LIQUID FORMATION IN SOME LOCATIONS NOW.METHODOLOGY: WE PLAN SEVERAL TASKS. FIRST WE WILL SIMULATE CURRENT MARS CLOUDS AND CLIMATE WITH A NEW CLIMATE MODEL THAT HAS ADVANCED AEROSOL AND CLOUD MODULES. WE WILL EXPLORE LITTLE STUDIED PHENOMENA FOR CURRENT MARS SUCH AS HIGH ALTITUDE CLOUDS AND THE CONDENSATION OF WATER AND CO2 AT NIGHT WHICH IS WIDESPREAD EVEN IN THE TROPICS AND MAY LEAD TO LIQUID WATER FORMATION NOW. ONCE WE HAVE CONFIDENCE THE MODEL IS REPRODUCING CURRENT DATA ON DUST AND ICE CLOUDS AND THEIR INTERACTIONS WITH THE SURFACE OUR SECOND TASK WILL BE TO SIMULATE ANCIENT MARS SO THAT WE CAN CONFIRM THE URATA AND TOON WORK USE BETTER PHYSICS TO ELIMINATE A NUMBER OF ASSUMPTIONS IN THE OLDER MODEL AND IMPROVE OUR UNDERSTANDING OF THE CLOUD PHYSICS. FINALLY WE WILL USE THE MODEL TO TIE INTO THE GEOLOGIC RECORD BY PREDICTING PRECIPITATION AND RUNOFF PATTERNS ON EARLY MARS AND THE STABILITY OF LAKES AND SEAS.RELEVANCE: OUR PROPOSED WORK IS DIRECTLY RELATED TO AN OBJECTIVE OF HABITABLE WORLDS RESEARCH "MARS-THEASTROBIOLOGICAL POTENTIAL OF PAST OR PRESENT ENVIRONMENTS ON OR IN THE MARTIAN SURFACE OR SUBSURFACE.