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Impact of Planetary Gravitation on High Precision Neutral Atom Measurements by Kucharek et al.

Abstract:Measurements of energetic neutral atoms (ENAs) have been extremely successful in providing very important information on physical processes inside and outside our heliosphere. For instance, recent IBEX observations provided new insights into the local interstellar environment and improved measurements of the interstellar He temperature, velocity, and direction of the interstellar flow vector. Since particle collisions are rare, and radiation pressure is negligible for these neutrals, gravitational forces mainly determine the trajectories of neutral He atoms. Depending on the distance of an ENA to the source of a gravitational field and its relative speed and direction this can result in a significant deflection and acceleration. In this paper we investigated the impact of the gravitational effects of the Earth, Moon, and Jupiter on ENA measurements performed in Earth orbit. The results show that current analysis of the interstellar neutral parameters by IBEX is not significantly affected by planetary gravitational effects. We further studied the possibility whether the Helium focusing cone of the Sun and Jupiter could be measured by IBEX and whether these cones could be used as an independent measure of the temperature of the interstellar Helium.

Fig. 3 of Kucharek et al. 2015: IBEX orbits during the spring (January–March) and fall (September–November) seasons. Shown is the flow direction of the interstellar neutrals, the orientation of the magnetopause and Earthʼs bow shock with respect to the Sun, and the orientation of the IBEX orbit and the FOV. This figure also shows the gravitational deflection by Earth relative to the Sun in fall and spring.
Fig. 8 of Kucharek et al. 2015: Ratio of nHe (r, 0) nHe (∞) for the Sun (left) and Jupiter (right) as a function of distance and temperature. The dashed line in the right-hand figure shows the unity line (nHe (r, 0) nHe (∞) = 1).