SM043-07
Martian crustal magnetic fields tend to decrease local ion escape
Tuesday, 15 December 2020: 07:24
Virtual
Tristan David Weber, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, David Brain, Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, CO, United States, Shaosui Xu, University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, United States, David Mitchell, Space Sciences Laboratory, University of California Berkeley, Berkeley, CA, United States, Jared R Espley, Goddard Space Flight Center, Greenbelt, MD, United States and James P McFadden, Univ California Berkeley, Berkeley, CA, United States
Abstract:
The crustal magnetic fields locked into the Martian surface provide a compelling natural laboratory in which we can investigate the influence that planetary magnetic fields have on ion escape. In these crustal fields, large loops of topologically closed magnetic field deflect incoming plasma and shield the atmosphere, effectively forming “mini-magnetospheres” that are expected to decrease ion escape. In between these loops, “cusps” of vertically oriented magnetic field are connected to the solar wind, facilitating energy input and potentially enhancing ion escape. The net effect that this system has on escape rates is not immediately clear.
Here we use data from the MAVEN spacecraft to investigate this question. Using measurements of ion fluxes, analysis of magnetic topology, and estimates of local particle magnetization we calculate ion escape rates across a range of crustal magnetic field strengths at Mars. We find that Martian crustal magnetic field structures tend to trap ions, leading to a buildup in density and a decrease in ion escape, but that this system is likely highly dependent on upstream solar wind conditions. By comparing the fluxes found in strong crustal field regions to those found in non-crustal field regions, we estimate that the presence of crustal fields tends to decrease global ion escape by 10-30%, a result that agrees with previous modeling studies. We also find that the presence of strong crustal field structures tends to decrease local ion escape by 50-80% as compared to escape above an unmagnetized surface. This result may hold implications toward the question of whether global magnetic fields are important for atmospheric retention.
