Solar wind charged particles interact with diffuse gas within the heliosphere, producing soft x-rays. This solar wind charge exchange (SWCX) process produces foreground emission that complicates interpretation of x-ray observations. In this work, we analyze x-ray observations of the western Galactic hemisphere by the Extended Roentgen Survey with an Imaging Telescope Array (eROSITA) instrument on the Spectrum-Roentgen-Gamma (SRG) spacecraft. These data avoid contamination by Earth’s geocorona and are derived from four surveys of the full sky, including during the minimum of the Sun’s activity cycle. We determine the SWCX contribution and subtract it from the survey, providing a less contaminated view of the diffuse soft x-ray sky. We also demonstrate that x-rays can be used to map the flow of interstellar matter through the Solar System.
Dennerl et al. (2026) studied this question.