Using Neutral Gas and Ion Mass Spectrometer Data to Characterize the Night Side of the Martian Atmosphere

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission seeks to answer the following question: where did the once-thick Martian atmosphere go? Characterizing the present day atmosphere is a necessary prelude to validating current models for extrapolation into the past. To address the aforementioned question, the mission uses the Neutral Gas and Ion Mass Spectrometer (NGIMS) to measure the mass density of key neutral and ion species in the upper Martian atmosphere. NGIMS obtains this data during deep dip campaigns in which the MAVEN spacecraft decreases the altitude of its orbit at closest approach from 140 km to 115-145 km.

This project focuses on using NGIMS density data for carbon dioxide, oxygen, carbon monoxide, and nitrogen during deep dip campaigns 5 and 6. Density profiles obtained from NGIMS were plotted against simulated density profiles from the Mars Global Ionosphere-Thermosphere Model (MGITM). Averaged temperature profiles were also plotted for the two deep dip campaigns, using NGIMS data and MGITM output. MGITM was also used as a tool to uncover potential heat balance terms needed to reproduce the mean density and temperature profiles measured by NGIMS.

This method of using MGITM as a validation tool for NGIMS data has been tested previously using dayside data from deep dip campaigns 2 and 8. In those cases, MGITM was able to accurately reproduce the measured density and temperature profiles; however, in the deep dip 5 and 6 campaigns, the results are not quite the same, due to the highly variable nature of the nightside thermosphere. MGITM was able to fairly accurately reproduce the density and temperature profiles for deep dip 5, but the deep dip 6 model output showed unexpected significant variation. The deep dip 6 results reveal possible changes to be made to MGITM to more accurately reflect the observed structure of the nighttime thermosphere. In particular, upgrading the model to incorporate gravity wave parameterization should better capture the role of wind in maintaining the nighttime thermospheric structure.

This project reveals that there still exist many unknowns about the structure and dynamics of the night side of the Martian atmosphere. Further study is needed to uncover these unknowns and their role in atmospheric mass loss.