Soft X-ray and ENA imaging of the Earth's dayside magnetosphere : OpenGGCM modeling results

Abstract:

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. Here, we use the OpenGGCM global magnetosphere-ionosphere MHD model and the Hodges model for the Earth’s exosphere to simulate both soft X-ray and ENA images of Earth's dayside cusps and magnetosheath in preparation for future mission planning. We consider several solar wind and IMF scenarios, such as a sudden increase in the solar wind dynamic pressure and southward IMF turning. We then predict the time-dependent variations in X-Ray and ENA images that would be observed by spacecraft far outside the magnetosphere. As expected, 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.