HOW DID MARS LOSE ITS ONCE EARTH-LIKE ATMOSPHERE? ION ESCAPE FROM HIGH ALTITUDES CONTRIBUTES SIGNIFICANTLY TO ATMOSPHERIC LOSS AT MARS BUT THE INITIAL ACCELERATION OF IONS FROM THE TOP OF THE ATMOSPHERE TO HIGH ALTITUDES HAS NOT YET BEEN INVESTIGATED. THE EFFICIENCY OF UPWARDS ION ACCELERATION ALONG WITH THE SUPPLY OF IONS AVAILABLE TO THE EXOBASE REGION (~200 KM ALTITUDE) LIMITS THE ION ESCAPE RATE AT MARS BUT THE RELATIVE IMPORTANCE OF THESE FACTORS IS UNKNOWN. DOES THE EXOBASE ACT TO THROTTLE ION ESCAPE CONTROLLING THE AMOUNT OF UPGOING IONS WHICH CAN BE EASILY ACCELERATED AWAY FROM THE PLANET? OR CONVERSELY ARE ACCELERATION PROCESSES INEFFICIENT AT REMOVING IONS FROM LOW ALTITUDES? THE PROPOSED STUDY IS A STATISTICAL ANALYSIS OF DATA COLLECTED AT ALTITUDES BETWEEN 120 KM AND 1000 KM BY THE SUPRATHERMAL AND THERMAL ION COMPOSITION (STATIC) INSTRUMENT ON THE MARS ATMOSPHERE AND VOLATILE EVOLUTION (MAVEN) SPACECRAFT AT MARS. STATIC MEASURES PARTICLE FLUXES AS A FUNCTION OF ENERGY ANGLE AND MASS FROM WHICH WE CAN DERIVE DENSITIES TEMPERATURES AND BULK VELOCITIES FOR THE MAJOR PLANETARY IONS. USING STATIC DATA PUBLICLY AVAILABLE ON THE PLANETARY DATA SYSTEM IT IS POSSIBLE TO INFER WHICH PROCESSES HEAT AND ACCELERATE IONS ABOVE THE EXOBASE. CHANGES IN THE MEASURED ION VELOCITY DISTRIBUTION FUNCTIONS WITH RESPECT TO ALTITUDE CAN BE SEARCHED FOR AND INTERPRETED TO FIND EVIDENCE OF SPECIFIC ACCELERATION AND HEATING MECHANISMS SUCH AS INTERACTIONS WITH WAVES OR AN AMBIPOLAR POTENTIAL. ONCE THOSE MECHANISMS ARE UNDERSTOOD THE NUMBER OF ESCAPING IONS CAN BE COMPARED TO THE SUPPLY OF IONS AT THE EXOBASE TO DETERMINE WHETHER THE ESCAPE RATE IS SOURCE- OR PROCESS-LIMITED. THIS ANALYSIS WOULD BE THE FIRST COMPREHENSIVE INVESTIGATION INTO THE PLASMA HEATING AND ACCELERATION PROCESSES OCCURRING IN AND ABOVE MARS IONOSPHERE. UNDERSTANDING THE PROCESSES OCCURRING AT MARS AND THE HISTORY OF ITS CLIMATE WERE IDENTIFIED AS HIGH-PRIORITY SCIENCE GOALS IN THE 2013-2022 PLANETARY SCIENCE DECADAL SURVEY. AN UNDERSTANDING OF THE FACTORS CONTROLLING ION ESCAPE WHICH THIS STUDY AIMS TO PROVIDE IS CRITICAL IN ORDER TO ACHIEVE THOSE GOALS. THE PROPOSED STUDY OF ION ESCAPE PROCESSES OCCURRING TODAY AT MARS WOULD IMPROVE EXTRAPOLATIONS BACK IN TIME ALLOWING FOR MORE ACCURATE CHARACTERIZATION OF THE PLANET S EARLY ATMOSPHERE. IN SECTION 4.3 OF THE 2014 SCIENCE PLAN THE PLANETARY SCIENCE DIVISION EXPRESSED THE GOALS TO UNDERSTAND HOW [THE OBJECTS IN THE SOLAR SYSTEM] FORMED AND EVOLVE AS WELL AS TO ADVANCE THE UNDERSTANDING OF HOW THE CHEMICAL AND PHYSICAL PROCESSES IN OUR SOLAR SYSTEM OPERATE INTERACT AND EVOLVE. THE ACCOMPLISHMENT OF THOSE OBJECTIVES IS IMPOSSIBLE WITHOUT COMPREHENSIVE STUDY OF ION ESCAPE PROCESSES AT MARS.