MESSENGER Observation on Reconnection and Structure of Mercury’s Magnetotail Lobes and Plasma Sheet

Monday, 14 December 2015: 16:40
2009 (Moscone West)
Gang Kai Poh1, James A Slavin1, Xianzhe Jia1, Jim M Raines2, Wei-Jie Sun3, Daniel J Gershman4 and Brian J Anderson5, (1)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (2)University of Michigan Ann Arbor, Department of Atmospheric, Oceanic and Space Sciences, Ann Arbor, MI, United States, (3)Peking University, School of Earth and Space Sciences, Beijing, China, (4)NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, United States, (5)Johns Hopkins University, Baltimore, MD, United States
Magnetic reconnection is known to be the most important process for plasma transport and energy conversion in space plasma. MESSENGER observations taken at Mercury have shown that magnetic reconnection is the dominant driver of magnetospheric dynamics and that it is significantly more intense than at Earth. Hence, Mercury provides a perfect natural laboratory to study the structure and reconnection at Mercury’s magnetotail as signatures of magnetic reconnections are expected to be more intense and prominent as compared to Earth and the outer planets. Using 4 years of MESSENGER’s magnetic field and plasma data, we analyzed 356 plasma sheet crossings. We determined that the B-field magnitude in the magnetotail lobe and plasma sheet follows a power law relation as a function of downstream distance |XMSM|. Statistical studies on the direction of Bz in the plasma sheet suggest that reconnection X-lines are most likely to occur at distance |XMSM| < 2.5RM. Assuming simple pressure balance, we have estimated the plasma beta β in the plasma sheet as a function of |XMSM|. Our results indicate that the beta is higher in the region where X-lines are usually found. Finally, we compared our results at Mercury with previous studies on the terrestrial magnetotail. Our results are consistent with the canonical idea that Mercury’s magnetotail is structurally similar to Earth’s but with shorter timescale due to more intense reconnection at Mercury.