Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p13b1320b&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P13B-1320
Physics
2780 Solar Wind Interactions With Unmagnetized Bodies, 5443 Magnetospheres (2756), 6225 Mars
Scientific paper
Atmospheric escape is known to occur at Mars today, and may have been the dominant loss process for the atmosphere since the end of the late heavy bombardment. Planetary ions escape to space through a number of different processes, including ion pickup, ion outflow, and bulk escape. Simulations and theoretical predictions suggest that bulk escape - or removal of coherent portions of ionospheric plasma - can contribute significantly to the total atmospheric escape rate, but there have been relatively few observational studies of this process. We present observations from Mars Global Surveyor (MGS) magnetometer and electron data of very strong (>100 nT) magnetic field signatures at 400 km altitudes near the Martian terminator, similar to plasmoids (flux ropes) observed in Earth's magnetotail. To our knowledge these are the strongest flux ropes reported at Venus or Mars, and may be the strongest sampled anywhere in the solar system. We will present the results of a statistical study that suggests that the plasmoids are observed downstream from regions of strong crustal magnetic field, at times of moderate or high solar wind pressure. We will present a case study that shows that the strongest plasmoid was observed shortly after a change in direction of the draped interplanetary magnetic field (IMF), and is filled with ionospheric plasma. These features clearly formed through interaction of the draped IMF and crustal magnetic anomalies, either through magnetic reconnection or a Kelvin-Helmholtz type instability. Either mechanism will result in removal of coherent portions of ionospheric plasma, indicating that we are observing bulk escape processes as they occur. We will present results of model fits of the total magnetic and plasma flux contained in the ropes, and the resulting implications for the role of bulk escape in Martian atmospheric evolution.
Brain David Andrew
Eastwood Jonathan P.
Halekas Jasper S.
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