Soft X-ray imaging

Soft X-ray emission from solar wind charge exchange (SWCX) recombination is ubiquitous throughout the solar system. It occurs in planetary atmospheres, comets, interplanetary space, the Earth’s exosphere, and likely in supernova remnants and other regions of astrophysical plasmas, making the study of charge exchange truly cross disciplinary.

The X-ray Imager (XRI)

Simulation of Soft X-ray and ENA images:

Charged ions and neutral atoms exchange electrons in many space plasma venues. Soft X-rays are emitted when highly charged solar wind ions, such as C6+, O7+, and Fe13+, interact with Hydrogen and Helium atoms. Energetic Neutral Atoms (ENAs) are produced when solar wind protons encounter neutral atoms. Consequently ENA and soft x-ray images can be a powerful technique to probe remotely the plasma and neutral density structures created when the solar wind interacts with planetary exospheres, such as those at the Earth, Moon, Mars, Venus, and comets. In preparation for future mission planning, soft X-ray and ENA images of Earth’s dayside magnetosheath are simulated during sudden increase of solar wind dynamic pressure and southward turning of interplanetary magnetic field (IMF), using OpenGGCM global magnetosphere MHD model and Hodges model of the Earth’s exosphere. 

Strong signals appear near to and define the positions of the bow shock, magnetopause, and cusps. The soft X-ray imager observes changes in the dayside system nearly instantaneously, while the ENA imager measures the changes later due to the finite travel time of ENAs from the dayside systems to the spacecraft location.

The top figures present solar wind and IMF conditions. The bottom figures present, from left to right, plasma density on the Ygse=0 plane, soft X-ray images observed by a virtual spacecraft at (Xgse, Ygse, Zgse) = (0, -45 Re, 0), and 1 keV Hydrogen ENA images observed by the same spacecraft.