Mercury's Nightside Magnetosphere Response to Southward IMF and ICMEs: MESSENGER Investigation and Comparisons With Earth’s Magnetosphere

The coupling between the solar wind and magnetosphere causes strong and distinct magnetospheric and geomagnetic activities, known as space weather on Earth. Mercury’s magnetosphere is structurally similar to Earth’s but differs in several important ways. Mercury does not have an ionosphere, but only a tenuous exosphere, and its magnetosphere faces stronger interplanetary magnetic fields (IMF) and lower Alfvénic Mach numbers than Earth due to its proximity to the Sun. These factors affect the coupling between the solar wind and the magnetosphere and the closure of field-aligned currents at low altitudes. However, few studies have explored the nature of the coupling at Mercury. This proposal will conduct a comprehensive comparison of the solar wind-magnetosphere coupling at Mercury and Earth. The results will be highly impactful and contribute broadly to our understanding of solar wind-magnetosphere coupling processes, especially the roles of the IMF and field-aligned current closure in magnetospheric dynamics and space weather at these two terrestrial-style magnetospheres. This project will support a Ph.D. student, an early career scientist, a female scientist, and international collaborations between the US and UK. The proposed project aims to comprehensively investigate the magnetospheric modes of Mercury’s magnetosphere and compare them with those observed in Earth’s magnetosphere. Magnetospheric response modes of flux circulations, including isolated substorms, steady magnetospheric convection, and sawtooth oscillations, are fundamental coupling modes and important space weather phenomena during solar wind-magnetosphere coupling. However, comprehensive investigations into the properties and driver conditions of magnetospheric modes in Mercury’s magnetosphere are lacking, as are comprehensive comparisons of the properties and drivers of similar processes between the magnetospheres of Earth and Mercury. We will analyze measurements from MESSENGER and compare them with the current knowledge and modes of similar processes in Earth’s magnetosphere. The specific science questions to be addressed include: i) investigating the response of Mercury’s magnetosphere to the southward interplanetary magnetic field (IMF) and interplanetary coronal mass ejections (ICMEs); ii) comparing similar processes to those in Earth’s magnetosphere; and iii) determining what can be learned from the comparison of similar processes between Earth and Mercury. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.