Abstract
Aims.The lack of an upstream solar wind plasma monitor when a spacecraft is inside the highly dynamic magnetosphere of Mercury limits interpretations of observed magnetospheric phenomena and their correlations with upstream solar wind variations.Methods.We used AMITIS, a three-dimensional GPU-based hybrid model of plasma (particle ions and fluid electrons) to infer the solar wind dynamic pressure and Alfvén Mach number upstream of Mercury by comparing our simulation results with MESSENGER magnetic field observations inside the magnetosphere of Mercury. We selected a few orbits of MESSENGER that have been analysed and compared with hybrid simulations before. Then we ran a number of simulations for each orbit (~30–50 runs) and examined the effects of the upstream solar wind plasma variations on the magnetic fields observed along the trajectory of MESSENGER to find the best agreement between our simulations and observations.Results.We show that, on average, the solar wind dynamic pressure for the selected orbits is slightly lower than the typical estimated dynamic pressure near the orbit of Mercury. However, we show that there is a good agreement between our hybrid simulation results and MESSENGER observations for our estimated solar wind parameters. We also compare the solar wind dynamic pressure inferred from our model with those predicted previously by the WSA-ENLIL model upstream of Mercury, and discuss the agreements and disagreements between the two model predictions. We show that the magnetosphere of Mercury is highly dynamic and controlled by the solar wind plasma and interplanetary magnetic field. In addition, in agreement with previous observations, our simulations show that there are quasi-trapped particles and a partial ring current-like structure in the nightside magnetosphere of Mercury, more evident during a northward interplanetary magnetic field (IMF). We also use our simulations to examine the correlation between the solar wind dynamic pressure and stand-off distance of the magnetopause and compare it with MESSENGER observations. We show that our model results are in good agreement with the response of the magnetopause to the solar wind dynamic pressure, even during extreme solar events. We also show that our model can be used as a virtual solar wind monitor near the orbit of Mercury and this has important implications for interpretation of observations by MESSENGER and the future ESA/JAXA mission to Mercury, BepiColombo.
Highlights
Mercury has a weak global magnetic field of internal origin that was first discovered by the Mariner 10 spacecraft in 1975– 1976 through three flybys of Mercury (e.g. Ness et al 1974)
Our primary intention is to estimate the upstream solar wind dynamic pressure and Alfvén Mach number that result in the best agreement between our hybrid simulations and the magnetic field observations; our main focus is the magnetospheric boundary determination
There is no change in the solar wind dynamic pressure between the two simulation runs, but we have shown in Fig. 10 that the dynamic magnetosphere of Mercury is highly controlled by the interplanetary magnetic field (IMF), which may affect the size and structure of the dayside magnetosphere; (2) as the orientation of the IMF changes, the magnetic reconnection sites change correspondingly, which highly affects the transport of the solar wind plasma into the magnetosphere and alters the dynamics and structure of the magnetosphere; and (3) in all the above-mentioned studies that discuss the location of the dayside magnetopause and
Summary
Mercury has a weak global magnetic field of internal origin that was first discovered by the Mariner 10 spacecraft in 1975– 1976 through three flybys of Mercury (e.g. Ness et al 1974). The interplanetary magnetic field (IMF) and the supersonic flow of the solar wind plasma are continuously interacting with the intrinsic magnetic field of Mercury, resulting in the formation of a “mini-magnetosphere”, that is qualitatively similar to Earth’s magnetosphere. This interaction forms a collision-less bow shock that decelerates and diverts the solar wind plasma and magnetic fields around the magnetospheric obstacle of Mercury (e.g. Anderson et al 2011a; Masters et al 2013), forms a magnetosheath with heated plasma between the bow shock and the magnetopause (e.g. Fairfield & Behannon 1976; Raines et al 2011), and creates an extended magnetotail with a central current sheet (e.g. Slavin et al 2010, 2012a; Sun et al 2015; Poh et al 2017)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
