MESSENGER and Mariner 10 flyby observations of magnetotail structure and dynamics at Mercury

• Published in: Journal of Geophysical Research: Space Physics Vol. 117; no. A1
• Main Authors: Slavin, James A., Anderson, Brian J., Baker, Daniel N., Benna, Mehdi, Boardsen, Scott A., Gold, Robert E., Ho, George C., Imber, Suzanne M., Korth, Haje, Krimigis, Stamatios M., McNutt Jr, Ralph L., Raines, Jim M., Sarantos, Menelaos, Schriver, David, Solomon, Sean C., Trávníček, Pavel, Zurbuchen, Thomas H.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-01-2012; American Geophysical Union
• Subjects: Atmospheric sciences; Boundary layers; Convection; Earth; Earth sciences; Earth, ocean, space; Exact sciences and technology; Magnetic fields; Magnetism; magnetosphere; magnetotail; Mercury; plasmoid; reconnection; TCR; Interplanetary magnetic field; magnetic field; strength; thickness; boundary layer; mercury; Magnetospheric substorm; Plasmoid; loading; convection; duration; Earth; dynamics; Magnetospheric tail; Low latitude; Power law; Mariner 10; Diameter; Reconfiguration; Traveling compression region
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2011JA016900

The first (M1), second (M2), and third (M3) MESSENGER flybys of Mercury traversed the planet's magnetotail from 1.25 to 3.25 RM downstream of the planet, where RM is Mercury's radius (2440 km). The encounters took place under northward, southward, and variable‐polarity interplanetary magnetic field (IMF), respectively. The magnetic field strength B in Mercury's magnetotail follows a power law decrease with increasing antisunward distance ∣X∣, B ∼ ∣X∣G, with G varying from −5.4 for northward to −1.6 for southward IMF. Low‐latitude boundary layers (LLBLs) containing strong northward magnetic field were detected at the tail flanks during two of the flybys. The observed thickness of the LLBL was ∼33% and 16% of the radius of the tail during M1 and M3, respectively, but the boundary layer was completely absent during M2. Clear signatures of tail reconnection are evident in the M2 and M3 magnetic field measurements. Plasmoids and traveling compression regions were observed during M2 and M3 with typical durations of ∼1–3 s, suggesting diameters of ∼500–1500 km. Overall, the response of Mercury's magnetotail to the steady southward IMF during M2 appeared very similar to steady magnetospheric convection events at Earth, which are believed to be driven by quasi‐continuous reconnection. In contrast, the M3 measurements are dominated by tail loading and unloading events that resemble the large‐scale magnetic field reconfigurations observed during magnetospheric substorms at Earth.
Key Points
Mercury's magnetotail resembles that of Earth, but with thicker boundary layers
Mercury exhibits both steady magnetospheric convection and subtorm‐type behavior
Reconnection and plasmoid ejection at Mercury reoccurs with a ~30 s periodicity