Hybrid simulations of Mercury’s global dynamics and the interplanetary ions’ precipitation fluxes under different interplanetary conditions

¹ Laboratoire de Physique des Plasmas (LPP), CNRS, Observatoire de Paris, Sorbonne Université, Université Paris-Saclay, École Polytechnique, Institut Polytechnique de Paris, Palaiseau 91120, France
² Laboratoire Atmosphères, Milieux et Observations Spatiales (LATMOS), IPSL, CNRS, UVSQ-Université Paris-Saclay, Sorbonne Université, CNES, Paris, France

^★ Corresponding author.

Received: 29 January 2025
Accepted: 11 July 2025

Abstract

Aims. We aim to quantify the impact of different interplanetary conditions met by Mercury along its orbit between its aphelion (~0.47 AU) and perihelion (~0.31 AU) on the Hermean environment, including the rate of solar-wind ion precipitation onto the surface.

Methods. We performed a set of 3D global hybrid simulations (kinetic ions and fluid electrons) with interplanetary conditions taken from recent statistics from observations on board the Parker Solar Probe and MESSENGER missions in such a way as to represent an average scenario at both the aphelion and perihelion positions, and in the cases of a slow (250 km/s) and fast (450 km/s) solar wind.

Results. The results are in general agreement with empirical models. However, we have found that the subsolar stand-off distances of magnetopause and bow shock, respectively, in the range of 1.0–1.4 R_M and 1.3–2.0 R_M, are relatively shorter than global statistical averages of, respectively, 1.45 and 1.96 R_M. We also observe a local time (LT) asymmetry in the cusp’s location, with the northern cusp located in the post-noon sector centred around 13–14.3 LT and the southern cusp located in the pre-noon sector centred around 9–10.7 LT. Noticeably, the southern cusp region takes the shape of a parallelogram extended from southern middle latitudes in the pre-noon sector to equatorial latitudes in the post-noon sector. We suggest that these effects could result from the orientation of the interplanetary magnetic field along the Parker spiral, which is characterised by an almost radial orientation with a small duskward component.