Magnetotail

A magnetotail is a region of a planet’s magnetosphere where the planetary magnetic field lines are stretched out into a long “tail” behind the planet. The name comes from analogy with the tail of a comet, which is similarly affected by the Sun’s gravity. Magnetotails form under conditions when the solar wind pressure exceeds the pressure of the planetary magnetic field. This can happen when a planet is closer to the Sun (such as during an eclipse), or when there is an outburst of solar activity (such as a coronal mass ejection).

The best-known example of a magnetotail is Earth’s, which was first observed in 1960 by Explorer 1, a satellite launched as part of the Space Race between the United States and Soviet Union. Earth’s magnetotail extends more than halfway to the Moon at its farthest point. It has two “lobes”, separated by a “current sheet” in which charged particles flow back and forth according to their electric charge. The northern lobe is called the magnetosheath, and is filled with plasma from the solar wind that has been deflected around Earth by its magnetic field. The southern lobe is called the magnetopause, and contains plasma that has been drawn out from Earth’s atmosphere by its magnetic field.

Magnetotails are important because they protect planets from harmful radiation and particles emitted by the Sun. They also play a role in atmospheric dynamics, including auroras (Northern Lights on Earth) and other electrical phenomena in space.