Magnetic reconnection and return flows in Venus’ magnetotail: case studies for Venus Express data

Venus lacks an intrinsic magnetic field, and its interaction with the solar wind and interplanetary magnetic field (IMF) creates an induced magnetosphere [1]. The IMF drapes around the planet, forming the magnetotail on Venus’ nightside, the main channel through which the ionospheric plasma escapes [2]. However, the ion escape in the magnetotail is reduced by unexplained flows that come back to Venus, i.e., return flows [3]. The process responsible for reversing the velocity of magnetotail ions remains unsolved. A possible mechanism causing the return flows is magnetic reconnection, a plasma process triggered by antiparallel magnetic field lines in the Venusian magnetotail. A plasmoid flowing toward Venus can be produced by reconnection. Such magnetic reconnection events have been identified by magnetic and plasma data collected by the Venus Express (VEX) spacecraft [4]. Here, we reassessed the VEX’s magnetometer (MAG) [5] and electron data using ASPERA-4/ELS [6] throughout the mission to identify typical Hall magnetic field signatures when the spacecraft crosses the plasma sheet, as well as electron energization, as evidence of the magnetic reconnection events [7]. We also systematically reassessed ion data (ASPERA-4/IMA) to identify return flow events when the ions are traveling in the direction toward Venus. In this presentation, we show several cases where we simultaneously detected the magnetic Hall field signature and ion return flows. These events are strong candidates for ion return flow associated with magnetic reconnection in the Venusian magnetotail. The ion speeds during these events are consistent with those predicted by reconnection theory. We will discuss the magnetic reconnection events and their possible role in triggering return flows in Venus’ magnetotail. [1] Futaana, Y., Stenberg Wieser, G., Barabash, S., & Luhmann, G. J. 2017, SSR, 212, 1453, doi: 10.1007/s11214-017-0362-8[2] Dubinin, E., Fränz, M., Zhang, T. L., et al. 2013, JGR, 118, 7624, doi: 10.1002/2013JA019164[3] Persson, M., Futaana, Y., Fedorov, A., et al. 2018, GRL, 45, 10805, doi: 10.1029/2018GL079454[4] Zhang, T.-L., Baumjohann, W., Lu, Q. M., et al. 2012, Science, 336, 567, doi: 10.1126/science.1217013[5] Zhang, T.-L., Berghofer, G., Magnes, W., et al. 2007, ESA Special Publication SP 1295 (Paris: ESA)[6] Barabash, S., Sauvaud, J., Gunell, H., et al. 2007, PSS, 55, 1772, doi: 10.1016/j.pss.2007.01.014[7] Yamada, M., Kulsrud, R., & Ji, H. 2010, RvMP, 82, 603, doi: 10.1103/RevModPhys.82.603