Solar orbiter detects ion sorting at the solar wind's magnetic boundary
A Southwest Research Institute (SwRI) study of data from the European Space Agency's (ESA) Solar Orbiter gives the most detailed view of the heliospheric current sheet (HCS) to date. The HCS is a sprawling, undulating surface emanating from the sun to beyond the solar system that serves as the boundary between the sun's north and south magnetic field hemispheres.
The European Space Agency's Solar Orbiter has captured unprecedented details of the heliospheric current sheet (HCS), a sprawling boundary separating the sun's magnetic poles. SwRI's Dr. Keiichi Ogasawara, the study's lead author, says the HCS functions as a high-speed pipeline, transporting vital information from the solar corona into space.
Scientists have long struggled to understand why the sun continuously ejects a supersonic stream of charged particles at over a million miles per hour, known as the solar wind. This wind affects space weather, Earth's auroras, and can disrupt satellite technology. The key to unlocking this mystery lies in magnetic connectivity. By tracking magnetic field lines to the solar surface, researchers can connect local surface activity directly to solar wind gusts.
The HCS provides an ideal connection point due to its distinct magnetic signatures. The new study, published in The Astrophysical Journal, offers valuable insights into the HCS's origin and composition, aiding in defining its relationship with the solar wind. As the sun rotates, the HCS twists like a "ballerina skirt," spiraling outward through the solar system and dividing the heliosphere into hemispheres with opposite magnetic field orientations.
One side pushes away from the sun, while the other pulls toward it. The Solar Orbiter recently passed through a fold of the HCS at approximately 26 million miles from the sun, closer than Mercury. Using its high-quality field, plasma, and composition instruments, the orbiter studied how particle populations behave in this enigmatic region.
Researchers found a clear and distinct change in the composition of ions within the HCS. The ratio of iron and oxygen ions decreases sharply at the magnetic sector boundary, suggesting that the HCS is not merely a magnetic feature but also influences how the sun sorts ions in the corona and releases them into the solar wind. While this data doesn't definitively explain the HCS's origin, it sets boundaries for future models and theories.
The findings provide a detailed, multifaceted view of an HCS crossing near the sun, showing organized variations in particle types and amounts within the plasma. This helps define what any successful theory on current sheet formation, solar wind heating, and magnetic connectivity must explain.
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