2:15 PM - 2:30 PM
[PCG23-09] Statistical study of heavy ion outflows from Mars observed by MAVEN
Keywords:Mars, atmospheric escape, carbon dioxide, MAVEN
In this study, we report on a statistical study of heavy ion outflows from Mars to investigate the influences of the local crustal magnetic fields and the direction of solar wind electric field on the ion outflows based on the MAVEN observations. The Supra-Thermal And Thermal Ion Composition (STATIC) instrument, the Solar Wind Ion Analyzer (SWIA), and the Magnetometer (MAG) data from July 2015 to March 2017 were used for the statistical study. We focused on the heavy ion outflows in the wake region. A fitting method enables us to derive densities of O+, O2+, and CO2+ ions separately. We estimated CO2+ number density by subtracting O2+ contamination. In order to eliminate the O2+ contamination in CO2+ mass range, we determined the response functions of the STATIC instrument to O2+ ions and calculated the CO2+ number densities from the data after the subtraction of O2+ distribution. Average density ratio of heavy ions in the magnetotail ion outflow is O+:O2+:CO2+ = 29:68:3.
We divided observed data by the location of the strong local crustal magnetic field around east longitude of 180 degrees into 4 local time groups: noon, dawn, dusk, and night. We also divided the data by locations of the ion outflow detection: upward E and downward E hemispheres in the Mars-Solar-Electric field (MSE) coordinates and north and south hemispheres in the Mars-Solar-Orbital (MSO) coordinates. The results show that number densities of heavy ions observed in the downward E hemisphere in the MSE coordinates tend to be higher than those observed in the upward E hemisphere, while the trend of heavy ion velocity is opposite. The results also show that the number fluxes of escaping heavy ions are similar in the both hemispheres, and fluxes observed in the upward E hemisphere tend to be smaller than those observed in the downward E hemisphere when the strong crustal magnetic field are located on the noon side. We will also report on other detailed features such as the energy and altitude dependences.