Observations of Horizontal Ionospheric Currents at Mars and Their Electrodynamic Effects
Tuesday, 24 May 2016: 12:15 PM
Matthew O. Fillingim1, Robert J Lillis1, Alexander Lee Fogle1, Dave A Brain2 and John E P Connerney3, (1)University of California, Berkeley, Space Sciences Laboratory, Berkeley, CA, United States, (2)University of Colorado at Boulder, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States
Abstract:
How the solar wind interacts with a planetary object depends upon the object's properties such as the presence of a magnetic field or an atmosphere. An unmagnetized object cannot stand-off the solar wind unless it possess a substantial atmosphere which can be ionized by solar radiation creating a conductive ionosphere. Currents can then be induced in the ionosphere; these currents can act to diminish the external solar wind magnetic field preventing it from reaching the surface. Here we present observations of currents in the ionosphere of Mars and also calculate their potential electrodynamic effects. Both Mars Global Surveyor, during aerobraking maneuvers, and, more recently, MAVEN measure the ambient magnetic field in the Martian ionosphere. From the observed changes in the local magnetic field, we are able to determine vertical profiles of horizontal ionospheric currents. Given an atmospheric model for MGS-era observations or in-situ atmospheric and ionospheric measurements from MAVEN, we also calculate the ionospheric conductivity. It is then straightforward to determine the electric field in the collisional ionosphere associated with these currents from a simplified Ohm’s law. In addition, the amount of Joule Heating in the ionosphere from the dissipation of these currents can be estimated. Finally, we consider the origin of these currents by comparing the observations to analytic estimates of currents in the ionospheric dynamo region driven by induced electric fields or by thermospheric winds. These results can give us insights into how external magnetic fields are effectively screened out by induced currents and how these induced currents can influence ionospheric dynamics around unmagnetized objects.
