Bow shock

[1] Bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind.

For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause.

For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium.

For instance, the charged particles making up the solar wind follow spiral paths along magnetic field lines.

[7] Bow shocks form at comets as a result of the interaction between the solar wind and the cometary ionosphere.

As it approaches the Sun, the heat of the sunlight causes gas to be released from the cometary nucleus, creating an atmosphere called a coma.

This allowed Rosetta to observe the bow shock as it formed when the outgassing increased during the comet's journey toward the Sun.

For several decades, the solar wind has been thought to form a bow shock at the edge of the heliosphere, where it collides with the surrounding interstellar medium.

However, data obtained in 2012 from NASA's Interstellar Boundary Explorer (IBEX) indicates the lack of any solar bow shock.

[13] Along with corroborating results from the Voyager spacecraft, these findings have motivated some theoretical refinements; current thinking is that formation of a bow shock is prevented, at least in the galactic region through which the Sun is passing, by a combination of the strength of the local interstellar magnetic-field and of the relative velocity of the heliosphere.

[15]Bow shocks are also a common feature in Herbig Haro objects, in which a much stronger collimated outflow of gas and dust from the star interacts with the interstellar medium, producing bright bow shocks that are visible at optical wavelengths.

The Hubble Space Telescope captured these images of bow shocks made of dense gasses and plasma in the Orion Nebula.

For unmagnetized and electrically conductive objects, the ambient field creates electric currents inside the object, and into the surrounding plasma, such that the flow is deflected and slowed as the time scale of magnetic dissipation is much longer than the time scale of magnetic field advection.

The induced currents in turn generate magnetic fields that deflect the flow creating a bow shock.

For example, the ionospheres of Mars and Venus provide the conductive environments for the interaction with the solar wind.

Magnetic draping has been detected around planets, moons, solar coronal mass ejections, and galaxies.