Parker spiral

The heliospheric current sheet is the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere. The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (Solar Wind). A small electrical current flows within the sheet, about 10⁻¹⁰A/m². The thickness of the current sheet is about 10,000 km near the orbit of the Earth.

The underlying magnetic field is called the interplanetary magnetic field, and the resulting electric current forms part of the heliospheric current circuit. The heliospheric current sheet is also sometimes called the interplanetary current sheet.

As the Sun rotates, its magnetic field twists into a Parker spiral, a form of an Archimedean spiral, as it extends through the solar system. This phenomenon is named after Eugene Parker's work: he predicted the solar wind and many of its associated phenomena in the 1950s. The spiral nature of the heliospheric magnetic field had been noted earlier by Hannes Alfvén, based on the structure of comet tails.

The influence of this spiral-shaped magnetic field on the interplanetary medium (solar wind) creates the largest structure in the Solar System, the heliospheric current sheet. Parker's spiral magnetic field was divided in two by a current sheet, a mathematical model first developed in the early 1970s by Schatten. It warps into a wavy spiral shape that has been likened to a ballerina's skirt. The waviness of the current sheet is because of the tilt angle of the Solar rotation axis with the ecliptic plane.

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