AUTHOR=Jung Jaewoong , Connor Hyunju Kim , Carter Jennifer A. , Koutroumpa Dimitra , Pagani Claudio 

TITLE=Exospheric neutral density at the 10 RE subsolar point during solar maximum: estimates from XMM soft X-ray observations

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 12 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2025.1568929

DOI=10.3389/fspas.2025.1568929

ISSN=2296-987X

ABSTRACT=Highly charged ions in the solar wind undergo charge exchange with neutral atoms in the Earth’s exosphere, particularly within the magnetosheath and cusps. This solar wind charge exchange process generates X-rays, which are expected to be crucial for imaging Earth’s dayside magnetosphere in the upcoming Lunar Environment Heliospheric X-ray Imager (LEXI) and Solar Wind Magnetosphere Ionosphere Link Explorer (SMILE) missions. A key parameter in this process is the density of neutral hydrogen in the Earth’s exosphere. This study estimates the exospheric density during solar maximum using soft X-ray data from the XMM-Newton astrophysics observatory. We used the Open Geospace Global Circulation Model (OpenGGCM), a global MHD model, to calculate plasma density, velocity, and temperature, and then extracted the exospheric density from the soft X-ray data by deconvolving plasma contributions. Based on five XMM-Newton observations during the solar maximum period from 2000 to 2003, we estimate the exospheric density at the 10 RE subsolar point to range from 42.5 to 65.1 cm−3, which is higher than the density used in previous soft X-ray imaging studies. This increased density range suggests stronger X-ray signals for the LEXI and SMILE missions.