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messenger observations of magnetic reconnection in mercury's magnetosphereDuring 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, approx.14 nT, that implies a rate of reconnection approx.10 times the typical rate at Earth and a cross-magnetospheric electric potential drop of approx.30 kV. The highest magnetic field observed during this second flyby, approx.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 approx.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 approx.2 min. The TCR signatures changed from south-north, indicating tailward motion, to north-south, indicating sunward motion, at a distance approx.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.
Document ID
20090006001
Document Type
Preprint (Draft being sent to journal)
Authors
Slavin. James A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2009
Subject Category
Space Sciences (General)
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.