Retrieval and Distribution of Neutral and Ionic Species in the Martian Upper Atmosphere as Measured by MAVEN NGIMS

The Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, having arrived at Mars in September 2014, aims to determine the importance of atmospheric loss to space in the evolution of the planet's atmosphere, climate, and potential for habitability throughout its history. The Neutral Gas and Ion Mass Spectrometer (NGIMS) aboard MAVEN measures the composition, structure, and variability of neutral and ionic species in the Martian upper atmosphere from approximately 125 to 500 km. Since September 2014 NGIMS has directly measured the Martian atmosphere over more than 500 MAVEN science orbits, covering large swaths of latitude, longitude, solar zenith angle, and local solar time. The careful development of retrieval methods is necessary to accurately and precisely investigate the neutral and ionic composition of the Martian upper atmosphere, as well as the distribution of these component species. These retrieval methods must include the determination of fragmentation patterns for all relevant species, exacting subtraction of instrument background, and determination of the instrument's sensitivity to neutrals and ions in its three operating modes. In this talk, we will describe the methodology for determining NGIMS neutral densities and present some preliminary results on the spatial distribution of active species.