A Survey of the Anomalous Reconnection Layer on Mercury

Abstract

Anomalous reconnection layer (ARL) usually appears near the magnetopause when the solar wind is in low Alfvén Mach number. The structure of an ARL is similar to the magnetic reconnection outflow region, i.e., a decrease in the total magnetic field and an increase in the high-energy ion flux. The ARL is seldom observed in the Earth’s magnetospheric environment because the solar wind at Earth is mostly in high Alfvén Mach number regime. According to previous observations, the solar wind at Mercury is usually in low Alfvén Mach number. Therefore, we assume that such an ARL can be observed frequently near Mercury’s magnetopause. To test this assumption, we examined the magnetic fields and ion fluxes obtained at the Mercury’s magnetosheath by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. With 120 events of ARLs we identified from MESSENGER’s data, we validate the assumption that ARLs frequently appear on Mercury. These ARL events were extracted from the list of MESSENGER bowshock and magnetopause crossing times compiled by Winslow et al. [2013]. The number of the ARL events found on Mercury is much larger than those found on Earth. The thickness of each ARL was estimated from the data, finding that the ARLs occupy, on average, one-fifth the thickness of the magnetosheath for Mercury. This work helps deepen our understanding of the comparative magnetospheric environment of Mercury and Earth.

 

References

Winslow, R. M., B. J. Anderson, C. L. Johnson, J. A. Slavin, H. Korth, M. E. Purucker, D. N. Baker, and S. C. Solomon (2013), Mercury's magnetopause and bow shock from MESSENGER Magnetometer observations, J. Geophys. Res. Space Physics, 118, 2213–2227, doi:10.1002/jgra.50237.