Magnetic waves explain the mystery of the Sun’s corona

This discovery generated what is one of the long-standing open questions in astrophysics.


The different chemical composition of the Sun’s corona from the cooler inner layers has puzzled scientists for decades. One reason is that the Sun’s chromosphere’s magnetic waves exert a force that separates the Sun’s plasma into different components. Only the ion particles are transported into the corona while leaving neutral particles behind.

In a new study, scientists combined observations from a telescope in New Mexico, the United States, with satellites located near-Earth to identify a link between magnetic waves in the chromosphere and areas of abundant ionized particles hot outer atmosphere.

Lead author Dr. Deborah Baker (UCL Space & Climate Physics) said: “The different chemical compositions of the Sun’s inner and outer layers were first noted more than 50 years ago. This discovery generated what one of the long-standing open questions in astrophysics is.”

“The difference in composition is surprising, given that the layers are physically linked, and that matter in the corona originates in the innermost layer, the photosphere.”

“Now, thanks to a unique combination of ground-based and space-based observations of the solar atmosphere, carried out nearly simultaneously, it has been possible to definitively detect magnetic waves in the chromosphere and link these to an abundance of elements in the corona that are not found in the inner regions of the Sun.”

“Identifying the processes that shape the corona is crucial as we attempt to understand better the solar wind, a stream of charged particles flowing outward from the Sun, which can disrupt and damage satellites and infrastructure on Earth.”

“Our new findings will help us to analyze the solar wind and trace it back to where it is coming from in the Sun’s atmosphere.”

The existence of magnetic waves—vibrations of ions going a specific way—were first conjectured in 1942 and are believed to be created in large numbers of nanoflares, or mini explosions, taking place in the corona each second.

The exploration group behind the new paper traced the direction of the waves by displaying a range of magnetic fields and found that waves reflecting in the chromosphere appeared to be magnetically connected to areas of abundant ionized particles in the corona.

Dr. Marco Stangalini (Italian Space Agency and the National Institute of Astrophysics, Rome), a co-author of both papers, said: “The difference in chemical composition between the inner layer, the photosphere, and the corona is a feature not just of our own Sun, but of stars throughout the Universe. Thus, by observing our local laboratory, the Sun, we can improve our understanding of the Universe far beyond it.”

The two papers used observations acquired by IBIS, the high-resolution spectropolarimetric imager at the Dunn Solar Telescope in New Mexico, together with imaging from the EUV imaging spectrometer (EIS) on the Japan/UK/USA Hinode solar observatory (an instrument designed and built by a UCL-led team) and data from the NASA Solar Dynamics Observatory (SDO).

The study noted: “findings provide a foundation for future research using data from the Solar Orbiter, a European Space Agency-mission acquiring close-up images of the Sun.”

Journal Reference:
  1. Deborah Baker et al, Alfvénic Perturbations in a Sunspot Chromosphere Linked to Fractionated Plasma in the Corona, The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abcafd