bowshock

A bow shock is a curved shock front that forms upstream of an obstacle moving through a medium at a supersonic or superfast-ml flow, where the flow speed relative to the obstacle exceeds the characteristic wave speed of the medium. In magnetized plasmas, such shocks are typically collisionless and are shaped by the magnetic field and plasma properties rather than particle collisions.

In the solar system, the Earth’s magnetosphere generates a planetary bow shock on the dayside. The shock stands several Earth radii sunward of the planet and deflects and slows the solar wind, creating a magnetosheath of heated and compressed plasma between the shock and the magnetopause. Similar bow shocks form around other magnetized planets, while unmagnetized planets and comets produce induced or cometary bow shocks as the solar wind interacts with their atmospheres or comae.

The physics of bow shocks in space is described by magnetohydrodynamics with kinetic effects. The shock orientation relative to the upstream magnetic field—quasi-perpendicular versus quasi-parallel—strongly influences heating, particle reflection, and acceleration processes. Rankine–Hugoniot jump conditions apply in a magnetized context, but many microphysical processes operate collisionlessly, contributing to observed energetic particles and turbulence in the downstream region.

Bow shocks also occur around non-planetary objects, such as runaway stars moving through the interstellar medium, producing stellar bow shocks, and in various astrophysical environments where fast flows encounter obstacles. They are studied to understand space weather, particle acceleration, and the interaction of plasmas with obstacles.

Observationally, spacecraft measurements (in situ) and simulations—ranging from global MHD to kinetic models—are used to characterize their structure, dynamics, and impact on surrounding plasmas.