Work

Observations of Mercury’s Bow Shock Disappearance in Quiet Solar Wind

Year: 2026

Type: article

Abstract: We report the bow shock disappearing (BSD) events at Mercury under quiet solar wind conditions. Using data from the MESSENGER spacecraft, we identified eight BSD events. Assuming a representative solar wind velocity of 400 km s −1 , we calculated the critical solar wind densities required for the Alfvén Mach number to equal unity, at which point a bow shock cannot form. In all eight events, these critical densities were substantially lower than the typical solar wind densities at Mercury’s heliocentric distance. The resulting extremely low densities produced high Alfvén speeds, driving the solar wind Alfvén Mach number below unity and causing the bow shock to disappear. BSD events are rare and occur in markedly different space environments at Mercury, warranting detailed further investigation through multipoint observations by the BepiColombo mission.

Source: The Astronomical Journal

DOI: 10.3847/1538-3881/aea988

Authors: Peishan He, Xiaojun Xu, Qing Chang

Institutions: Macau University of Science and Technology, China National Space Administration, Shandong Institute of Advanced Technology

Language: English

Topic: Ionosphere and magnetosphere dynamics

Subfield: Space and Planetary Science

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $4,499

Funders: National Natural Science Foundation of China, Fundo para o Desenvolvimento das Ciências e da Tecnologia