What Does Ion Escape at Mars Depend On? Examining the Correlation Between Different Upstream Solar Wind Drivers and Ion Loss at Mars

Does an intrinsic planetary magnetic field protect a planet's atmosphere from space weather and stellar winds? Within our solar system, in what ways does the solar wind drive atmospheric escape? To take a step towards answering these questions, we evaluate the correlation between upstream solar wind drivers and ion loss at Mars. Atmospheric ion escape is one of several processes of atmospheric loss and it is a particularly effective process for removing species heavier than hydrogen and helium from terrestrial atmospheres. Mars lacks an intrinsic planetary magnetic field. For Earth, the main magnetic field prevents the solar wind from directly interacting with our habitable atmosphere. However, it is unclear to what extent a geodynamo protects the atmosphere versus enhances ion escape. We aim to examine the correlation between upstream solar wind drivers (e.g., upstream solar wind dynamic pressure or solar wind electromagnetic energy flux / Poynting flux) and global ion loss at Mars, with an eventual aim of doing the same at Earth and Venus to better understand the importance of planetary magnetic fields and solar wind parameters in atmospheric loss.

We utilize data from MAVEN's magnetometer, solar wind ion analyzer, and suprathermal and thermal ion composition instrument for November 2014 through January 2022. We limit ion flux data to observations at an altitude of 1.25-1.45 RMars and to energies below 200 eV. We convert data into the Mars-Solar-Electric coordinate system, which is determined by the solar wind and IMF directions. For each solar wind driver, we analyze the driver's distribution and create bins of different values (e.g., for Poynting flux, there are 23 bins with the bins' mean Poynting flux values ranging from 1.1e-4 mW/m2 to 1.5e-2 mW/m2). The planetary ion flux data corresponding to each upstream driver's bin is gridded across Mars and the radial component of planetary ion flux is determined so that the inwards (returning) and outwards (escaping) planetary ion fluxes may easily be determined. A global mean planetary ion flux is calculated for each upstream driver's bin so that we can then determine the correlation between planetary ion flux and the upstream drivers. This is performed for different upstream solar wind drivers and for the ion species of H+, O+, and O2+.