Solar wind boundaries around Mars
Unlike Earth, Mars has no strong global magnetic field to deflect the solar wind (coming from the left in this view). On the dayside of the planet the solar wind is compressed as it approaches Mars and, in the absence of a strong global magnetic field, interacts directly with the planet's ionized atmosphere (ionosphere).
The interaction results in the formation of two clear boundaries: the bow shock (BS) and the magnetic pile-up boundary (MPB). At the bow shock the solar wind is decelerated from supersonic to subsonic speed as its flow is obstructed by Mars. Closer to the planet's surface is the MPB, which is the top of the induced magnetic field. The induced field originates from the magnetic field that is carried by the solar wind which gets compressed at Mars and is draped around the planet.