Abstract: Continuous monitoring of the solar wind ion composition is essential for understanding solar-terrestrial interactions, especially the Solar Wind Charge Exchange (SWCX) signal. The SWCX signal, a soft X-ray emission (<2 keV), arises from interactions between highly ionised solar wind particles (e.g., O7+, O8+, C6+) and neutral atoms. This emission is ubiquitous across the solar system, occurring wherever the solar wind meets interstellar neutrals within the heliosphere or interacts with planetary environments such as those of Mars, Venus, Jupiter, Pluto, and Earth.

In this talk, we will explore how SWCX emissions from Earth's exosphere, as observed by the astrophysical telescope XMM-Newton, can be used to infer solar wind composition through spectral analysis. This research is particularly critical given the degradation of the heavy ion spectrometer aboard the Advanced Composition Explorer (ACE), a solar wind monitor at L1, which has left us without reliable near-Earth ion composition data since 2011. We will also discuss the potential contributions of the upcoming SMILE mission to solar wind composition monitoring. SMILE is due to launch in 2025 and it aims to capture large-scale magnetopause dynamics through soft X-ray imaging.