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Peer-reviewedCC BY 4.0The Astronomical Journal

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

  • Peishan He1,2
  • Xiaojun Xu1,2
  • Qing Chang3
  1. 1Macau University of Science and Technology
  2. 2CNSA Macau Center for Space Exploration and Science
  3. 3Shandong Institute of Advanced Technology (SDIAT)
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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.

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Cite

BibTeXRIS
BibTeX
@article{he2026observations,
  title = {{Observations of Mercury’s Bow Shock Disappearance in Quiet Solar Wind}},
  author = {Peishan He and Xiaojun Xu and Qing Chang},
  journal = {The Astronomical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-3881/aea988},
  url = {https://iopscience.iop.org/article/10.3847/1538-3881/aea988},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Observations of Mercury’s Bow Shock Disappearance in Quiet Solar Wind
AU  - Peishan He
AU  - Xiaojun Xu
AU  - Qing Chang
PY  - 2026
DA  - 2026/10/16
JO  - The Astronomical Journal
DO  - 10.3847/1538-3881/aea988
UR  - https://iopscience.iop.org/article/10.3847/1538-3881/aea988
AB  - 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.
SN  - 0004-6256
SN  - 1538-3881
ER  -