Modeling the Magnetospheric 3D X‐Ray Emission From SWCX Using a Cusp‐Magnetosheath Emissivity Model

Abstract A major challenge in solar‐terrestrial physics is to understand the large‐scale dynamics of planetary magnetospheres, such as the motion of the Earth's magnetopause. Currently, a combination of in situ measurements and numerical modeling has been used to address this challenge, but no global imaging has been available. The discovery of soft X‐rays by the solar wind charge exchange (SWCX) process offers an opportunity to image the emitted X‐ray photons. The SMILE mission, due for launch in late 2025, will carry a wide field of view soft X‐ray telescope designed to observe emission from the magnetosheath and cusps. As no emission is expected from within the magnetosphere, it is expected that the magnetopause boundary will be observable from changes in X‐ray intensity across the boundary. Extracting the 3D magnetopause boundary from the 2D X‐ray images is a challenging task and several methods have been developed to model it. One method is to create a 3D emissivity model and adjust its parameters to fit the 2D X‐ray image. In this paper, we develop a Cusp and Magnetosheath Emissivity Model (CMEM) and compare its performance to a previous model that did not include the cusps. We find CMEM has an improved fit to emissivity simulations for a wide range of solar wind densities, but that a poor choice of initial parameters can generate unphysical fits in both models. We propose and verify a method to resolve this that uses the upstream solar wind density to constrain some of the initial parameters.