The density distribution and 58.4 nm radiation intensity of interstellar helium in the heliosphere: a model simulation

Research on the interstellar medium and its interaction with the solar system constitutes a significant topic in planetary physics. As the Sun traverses the local interstellar cloud, interstellar neutrals penetrate the heliosphere, forming the interstellar wind, and scattering solar extreme ultraviolet (EUV) emission lines. The intensity of the scattered radiation provides an indicator of the characteristic parameters of the interstellar wind, crucial for characterizing the heliosphere, the interstellar medium, and the evolution of the solar system. Meanwhile, a powerful method for studying stellar evolution is investigating the EUV emissions of stars. The only ongoing mission conducting an EUV full-sky survey is the relay satellite Queqiao-2. Due to the strong absorption of the interstellar medium at EUV wavelengths, modelling is essential to any study of these influences. In this study, we reviewed classical modelling methods for the density distribution of the interstellar helium atoms in the heliosphere, and the corresponding 58.4 nm radiation intensity. We established distinct density and intensity models for different orbital positions of Earth’s revolution. We found that when the Earth enters the helium focusing cone in the downwind region, both the helium density and the 58.4 nm radiation intensity increase rapidly, with the temperature effect being particularly important. The radiation intensity in the downwind direction can be 170 times that of the upwind direction. Some negligible factors were omitted for simplicity, such as the effects of the solar line width and Doppler shift. Our research can serve as an aid to the interpretation of the EUV observations in the full-sky survey conducted by Queqiao-2.