Journal article
Ion Composition Boundary Layer Instabilities at Mars
Geophysical research letters, Vol.46(17-18), pp.10303-10312
09/01/2019
DOI: 10.1029/2019GL084779
Abstract
The ion composition boundary layer that separates solar wind from ionospheric plasma at Mars typically contains a smooth compositional transition. However, ~10% of boundary crossings display large nonmonotonic variations in density, indicating an instability. We find that most of these instabilities occur on the flanks or downstream of the planet, and many fall into two distinct classes, which occur in different locations, under different preferred conditions. Plume events, which occur where the solar wind electric field points outward, likely represent the motion of the escaping ion plume across the spacecraft. Snowplow events, which occur where the electric field points inward, likely represent the escape of discrete parcels of plasma, which could account for ~10% of the total ion loss from Mars. Snowplow events occur under conditions that favor the development of ionospheric irregularities, which could form a seed for the snowplow mechanism that detaches and accelerates ionospheric plasma downstream.
Plain Language Summary
The solar wind, a hot ionized gas—or plasma—that flows from the Sun, interacts directly with plasma derived from the Martian atmosphere, across a boundary layer known as the ion composition boundary. Usually, this boundary layer has a stable structure and contains smoothly varying densities of planetary and solar wind ions. However, at some times, large nonmonotonic variations in density across this boundary layer suggest a rippled and/or unsteady boundary, indicating the presence of some instability. We investigate these unstable cases, and find that they fall into two distinct classes. Plume events likely represent a flapping motion of a discrete plume of escaping ions. Snowplow events likely represent the escape of discrete clouds of plasma from the boundary layer. These two types of events occur in different locations, under different conditions. These trends help reveal the coupling between the Martian upper atmosphere, the ionosphere, the magnetosphere, and the solar wind.
Key Points
Instabilities occur near the boundary layer between ions of solar wind origin and ions of ionospheric origin at Mars
We identify two distinct classes of boundary layer instabilities, which have different characteristics, and occur in different locations
Snowplow events, a potentially significant ion loss mechanism, occur under conditions that favor an irregular ionospheric structure
Details
- Title: Subtitle
- Ion Composition Boundary Layer Instabilities at Mars
- Creators
- J. S. Halekas - University of IowaS. Ruhunusiri - University of IowaJ. P. McFadden - University of California, BerkeleyJ. R. Espley - Goddard Space Flight CenterG. A. DiBraccio - Goddard Space Flight Center
- Resource Type
- Journal article
- Publication Details
- Geophysical research letters, Vol.46(17-18), pp.10303-10312
- DOI
- 10.1029/2019GL084779
- ISSN
- 0094-8276
- eISSN
- 1944-8007
- Number of pages
- 10
- Grant note
- MAVEN
- Language
- English
- Date published
- 09/01/2019
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984429020302771
Metrics
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