Ion Acceleration Processes Near the Martian Exobase
Abstract
Ion escape from Mars occurs at high energies in the ion plume and at lower energies down the magnetotail. From their source region in the upper atmosphere/ionosphere, ions can be accelerated by multiple processes (e.g., magnetic tension forces, convection electric fields, ambipolar potentials, and wave heating) before they are ultimately lost from the system. Some of these processes require that ions first be energized to reach high altitudes; however, the initial acceleration of ions in the vicinity of the exobase ( 200 km altitude) is not well understood.
To address this issue, we use data collected by the Mars Atmosphere and Volatile Evolution Mission (MAVEN), which has an elliptical orbit that samples altitudes from several scale heights below to well above the exobase. Using data from the SupraThermal And Thermal Ion Composition (STATIC) instrument, we calculate ion density, temperature, and velocity moments in the vicinity of the exobase. Below the exobase, O2+ and O+ distributions are generally well characterized by drifting Maxwellians, but at higher altitudes a suprathermal tail develops. Using the characteristics of these ion distributions in combination with information about the local magnetic topology, we begin to characterize the initial acceleration of ions at low altitudes, with the goal of understanding the physical process(es) responsible.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSM23D3215H
- Keywords:
-
- 2740 Magnetospheric configuration and dynamics;
- MAGNETOSPHERIC PHYSICSDE: 2799 General or miscellaneous;
- MAGNETOSPHERIC PHYSICSDE: 5435 Ionospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5443 Magnetospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS