An article published in “The Astrophysical Journal Letters” offers a solution to the mystery of the local magnetic field inversion in the solar atmosphere, called switchback in jargon, observed in recent decades. A team of researchers with an important participation from the Italian National Institute of Astrophysics used detection conducted with the Solar Orbiter space probe’s METIS instrument to test the theories produced over the years.
The first inversions of the local magnetic field in the solar atmosphere were detected in the 1970s by the Helios 1 and 2 space probes. Their duration ranged from a few seconds to a few hours and then the magnetic field returns to its previous direction. Subsequent solar missions detected this phenomenon, including NASA’s Parker Solar Probe up to the Solar Orbiter’s detection.
Launched on February 20, 2020, the Solar Orbiter space probe aims to carry out several studies of the Sun. This ESA mission, with a NASA collaboration, conducted a relatively close passage to the Sun at the end of last March, reaching a shorter distance than the planet Mercury’s. On March 25, the METIS coronagraph conducted solar measurements which, according to the authors of this study, led to the solution of the mystery.
The top image (ESA & NASA/Solar Orbiter/EUI & Metis Teams and D. Telloni et al. (2022)) shows the Sun as seen by the Solar Orbiter space probe on March 25, 2022. The central image was captured by the EUI instrument (Extreme Ultraviolet Imager) while the outer one was captured by the METIS coronagraph, which blocks the light on the solar surface in order to detect the tenuous outer atmosphere, called the corona. The switchback is the white/light blue structure on the left side.
According to the authors of this study, the mechanism that generates these phenomena is the one proposed by Professor Gary Zank of the University of Alabama in Huntsville, USA. This theory examines the different ways in which magnetic regions near the solar surface interact with each other.
The bottom image (Courtesy Zank et al. (2020)) shows the mechanism of generating a switchback. In (a) active regions on the Sun may have open or closed magnetic field lines. In (b) there’s an interaction between a magnetically open and a closed region resulting in the creation of a field line with an S-like shape and the production of an outburst of energy. In (c) the field lines react to the generation of the S-shape by releasing energy with an outward propagation, the switchback. A similar switchback is sent in the opposite direction, into the sun.
The next step of the research will consist in looking for a statistical link between the switchbacks observed on site and the solar regions from which they originate. Basically, a spacecraft will have to fly through the inverted magnetic field and see what happened on the Sun’s surface. This work could be done by the Solar Orbiter or by another probe such as the Parker Solar Probe, which would be another result of the collaboration between ESA and NASA.
The next close passage to the Sun of the Solar Orbiter space probe will take place on October 13. Observing various layers of the Sun’s atmosphere will provide more information on magnetic field reversals and other phenomena. For example, the authors of this study are interested in the origin of the slow solar wind, another mystery to be solved. The conditions on the Sun’s surface and near it make studies difficult but gradually, scientists are understanding the various processes taking place.