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Why is Earth’s magnetosphere shaped like a teardrop?

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Diagram of Earth's atmosphere layers-troposphere, stratosphere, mesosphere, and thermosphere-showing how temperature and air pressure change with increasing altitude, with key features like the ozone layer and pressure percentages at various heights. — Ionosphere and magnetosphere The layers of Earth's atmosphere, with a yellow line showing the air temperature at various heights.

Earth’s magnetosphere is shaped like a teardrop primarily due to its interaction with the solar wind, a continuous stream of charged particles flowing from the Sun.12

On the dayside, the pressure of the solar wind compresses Earth’s magnetic field to a distance of approximately 10 Earth radii (about 65,000 km). At this boundary, known as the magnetopause, the pressure of the solar wind is balanced by the geomagnetic field, which acts as an obstacle and deflects the solar wind around the planet via a bow shock.123

Conversely, on the nightside, the forces associated with the magnetic field and the solar wind act in parallel. This allows the magnetosphere to stretch into an elongated magnetotail that extends millions of kilometres away from the Sun. This combination of a compressed sunward boundary and a trailing, elongated tail gives the magnetosphere its characteristic teardrop or comet-like shape.123