Science Seminars

2/2/2009 – MESSENGER Observations of Magnetic Reconnection in Mercury’s Magnetosphere

Speaker: Dr. James A. Slavin, Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland
Date: Monday, Feb 02, 2009
Time: 4:00pm
Location: LSTB A200

Seminar Abstract:

During MESSENGER’s second flyby of Mercury on October 6, 2008, very intense reconnection was observed between the planet’s magnetic field and a steady southward interplanetary magnetic field (IMF). The dawn magnetopause was threaded by a strong magnetic field normal to its surface, ~ 14 nT, that implies a rate of reconnection ~10 times the typical rate at Earth and a cross-magnetospheric electric potential drop of ~ 30 kV. The highest magnetic field observed during this second flyby, ~160 nT, was found at the core of a large dayside flux transfer event (FTE). This FTE is estimated to contain magnetic flux equal to ~5% that of Mercury’s magnetic tail or approximately one order of magnitude higher fraction of the tail flux than is typically found for FTEs at Earth. Plasmoid and traveling compression region (TCR) signatures were observed throughout MESSENGER’s traversal of Mercury’s magnetotail with a repetition rate comparable to the Dungey cycle time of ~ 2 min. The TCR signatures changed from south-north, indicating tailward motion, to north-south, indicating sunward motion, at a distance ~ 2.6 RM (where RM is Mercury’s radius) behind the terminator indicating that the near-Mercury magnetotail neutral line was crossed at that point. Overall, these new MESSENGER observations suggest that magnetic reconnection at the dayside magnetopause is very intense relative to what is found at Earth and other planets, while reconnection in Mercury’s tail is similar to that in other planetary magnetospheres, but with a very short Dungey cycle time.